This paper presents a comparative study on the mechanical properties of seven monofilaments of 0.... more This paper presents a comparative study on the mechanical properties of seven monofilaments of 0.12 mm diameter made with different polymeric materials including PET, PBT, PE, PP, and PA6 in order to assess their suitability for being spacer yarns for developing high-quality spacer fabrics. Their support capability and elasticity corresponding to fabric compression resistance and resilience, respectively, were evaluated by analyzing the tensile stress–strain relationships and residual strains of monofilaments subjected to cyclic tensile loading. Slack and taut heat setting on the monofilaments were also considered to select a proper heat setting method for their spacer fabrics. The mechanical properties of the monofilaments were explained by using the supramolecular structure information from X-ray diffraction and sonic orientation tests. The results showed that PET monofilaments have much higher moduli than the other monofilaments and possess better support capability as spacer yar...
Water transfer through porous textiles consists of two sequential processes: synchronous wicking–... more Water transfer through porous textiles consists of two sequential processes: synchronous wicking–evaporating and evaporating alone. In this work we set out to identify the main structural parameters affecting the water transfer process of cotton fabrics. Eight woven fabrics with different floats were produced. The fabrics were evaluated on a specially designed instrument capable of measuring the water loss through a vertical wicking process. Each test took 120 min, and two phases were defined: Phase I for the first 10 min and Phase II for the last 110 min according to wicking behavior transition. Principal components and multivariate statistical methods were utilized to analyze the data collected. The results showed that Phase I dominated the whole wicking–evaporating process, and the moisture transfer speed in this phase varied with fabric structure, whereas the moisture transfer speeds in Phase II were similar and constant regardless of fabric structure. In addition, fabric with m...
Three-dimensional mesh fabric is a special type of knitted spacer fabric with sandwich structure ... more Three-dimensional mesh fabric is a special type of knitted spacer fabric with sandwich structure consisting of two separate meshed multifilament outer layers linked together with a layer of spacer monofilaments. It has found wide applications in home textiles and automotive industry due to its good energy-absorbing performance and ventilation property. This article presents a comprehensive structural analysis on a mesh spacer fabric of thickness 10.3 mm in order to place a solid foundation to enhance the understanding of the structural features and mechanical behavior. The real geometric structure was reconstructed by scanning the fabric via Micro X-ray computed tomography. The spacer monofilaments and meshed outer layers were analyzed quantitatively based on the Micro X-ray computed tomography reconstruction. It was found that the spacer monofilaments are different in length, curvature, and torsion. The spacer monofilament lengths can be ranging from 9.43 to 10.77 mm. Their curvatu...
Textile strain sensors capable of monitoring human physiological signals and activities have grea... more Textile strain sensors capable of monitoring human physiological signals and activities have great potential in health monitoring and sports. Integrating them into apparel to be wearable, repeatable, and sensitive remains a great challenge, impeding their practical applications. This paper reports a fabric strain sensor that can be seamlessly integrated into various apparel under precise tension through industrial‐scale production. A conductive core‐sheath polyester/carbon black multifilament (CSPCF) produced on a melt spinning machine is wrapped onto a spandex yarn via a yarn covering machine to manufacture a stretchable double‐covered conductive yarn (DCCY). The fabric strain sensor is specially designed and automatically produced on an industrial knitting machine by precisely integrating the DCCY into an elastic fabric. The sensing principle is contact and separation between neighboring spiral CSPCFs by stretching an arched “rainbow spring” like DCCY embedded in the fabric. The sensor has a high sensitivity of 2% strain detection limit, excellent durability and repeatability for 10 000 cycles, and a wide sensing range of 60% strain, even in a wet state or after repeatedly washing, bending, or rubbing. Three wearable products, by seamlessly integrating the sensor, are demonstrated to effectively and quantitatively detect bending motions of finger, elbow, and knee. Integrating textile strain sensors into apparel is a great challenge but a prerequisite for practical applications. This work presents a fabric strain sensor with arched double‐covered conductive yarn detecting strains through “rainbow spring” like contact and separation of the spiral core‐sheath PET/carbon black multifilaments. A knitted sensing fingerstall by seamle
3D spacer fabrics are a type of sandwich structure consisting of two separate multifilament fabri... more 3D spacer fabrics are a type of sandwich structure consisting of two separate multifilament fabric outer layers linked together with a layer of spacer monofilaments. They have been widely used as energy absorbing materials and composite reinforcement. The microstructure features and compression behavior of a typical spacer fabric were investigated experimentally and numerically in this study. Eight unit cells with 64 spacer monofilaments were reconstructed from scanning of the fabric via Micro X-ray computed tomography (μCT). The geometric variations of the reconstructed spacer monofilaments were analyzed quantitatively. It was found that spacer monofilaments in different unit cells are different in length, curvature and torsion. A series of FE models based on different numbers and combinations of the identified unit cells were created. The FE simulation results showed that the geometric variations of spacer monofilaments have strong influence on the compression behavior , and the model with shorter length, lower curvature and torsion of spacer monofilaments has higher compression resistance. The compression resistance in the densification stage of the fabric increases with increasing the number of spacer monofilaments adopted due to more evident interactions among spacer yarns. This study provides an in-depth understanding on the compression behavior of spacer fabric.
The use of 3D knitted spacer fabrics made of polymeric fiber materials as vibration isolators is ... more The use of 3D knitted spacer fabrics made of polymeric fiber materials as vibration isolators is proposed in this study by considering their spacer monofilaments as Euler springs which have been proved to be excellent vibration isolators. Three types of spacer fabrics with different compression force–displacement characteristics were fabricated by varying monofilament diameter and fabric thickness. Their vibration transmissibility under harmonic vibration testing conditions was measured by an electromagnetic shaker. It is found that the resonant frequency and isolation frequency of these fabrics decrease with increasing acceleration level and load mass, and a thicker fabric has better vibration isolation performance due to its lower resonant and isolation frequencies. The study shows that 3D knitted spacer fabrics can be designed as good human vibration isolators without compromising their comfort.
This part presents a dynamic model for predicting the impact compressive responses of warp-knitte... more This part presents a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics
under various loading conditions using quasi-static compressive stress–strain data. The model was established based on a nonlinear mass-spring-damper system by considering spacer yarns as nonlinear springs with damping effect and representation of their stiffness by the constitutive model developed in Part I. Based on the dynamic model, the impact compressive responses of a typical warp-knitted spacer fabric was parametrically studied in terms of damping ratio, initial velocity, striker mass and contact area. The study indicates that damping can reduce the peak acceleration and peak displacement regardless of loading conditions, and the increase of the initial velocity can enhance the damping effect. Increasing initial velocity or striker mass while keeping the counterpart constant can increase the peak acceleration and peak displacement. However, at a constant kinetic energy, either increasing striker mass or decreasing initial velocity can reduce the peak acceleration, but the peak displacement keeps constant. The study also shows that an optimal size of the spacer fabric exists for achieving minimal peak acceleration under impact at a certain kinetic energy. Experimental validation by drop-weight impact tests demonstrates that the predictions of the dynamic model are in satisfactory agreement with the experimental results. Using the quasi-static compressive data from a simple test, this dynamic model can numerically simulate the full time-response of warp-knitted spacer fabrics under various impact conditions.
This paper presents a theoretical study of the compressive mechanics of warp-knitted spacer fabri... more This paper presents a theoretical study of the compressive mechanics of warp-knitted spacer fabrics. The first part, as
presented in the current paper, focuses on the establishment of a constitutive model that can give accurate compressive stress–strain relationships of warp-knitted spacer fabrics. Based on the analysis of three existing models for polymeric or metallic foams, a constitutive model consisting of seven parameters was firstly proposed for spacer fabrics. The effect of each parameter on the regressive stress–strain curves was then parametrically studied. Experimental validation was finally conducted by using 12 warp-knitted spacer fabrics produced with different spacer monofilament diameters and inclination angles, fabric thicknesses, and outer layer structures to identify the physical sense of the parameters. The analysis has showed that an excellent agreement exists between the regressive and experimental results, and all seven parameters have a quantitative effect on a particular phase of the resultant compressive stress–strain curves of warp-knitted spacer fabrics. The change of each parameter makes a clear physical sense on the stress–strain curve. Therefore, the proposed constitutive model can be used as a useful tool to engineer the cushioning properties of warp-knitted spacer fabrics. The adoption of the constitutive model to develop a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics under various loading conditions will be presented in Part II.
International Journal of Mechanical Sciences 94-95(2015)244–259, Mar 9, 2015
3D finite element (FE) analysis was conducted to investigate the mechanical behaviour of a typica... more 3D finite element (FE) analysis was conducted to investigate the mechanical behaviour of a typical 3D spacer fabric structure under compression in terms of its structure feature and mechanical properties of its components. A spacer fabric consists of two separate outer layers joined together with spacer monofilaments. Six FE models with different constraints on the spacer monofilaments and outer layer thicknesses were created using the precise geometry of a unit cell from Micro X-ray computed tomography (μCT) scanning by fully considering the yarn interactions among all the fabric components and material's nonlinearity. A FE model which could give a satisfactory prediction of the compression load–displacement relationship of the fabric was employed to identify the compression mechanism. It was confirmed from the simulation that the nonlinear compression behaviour of the 3D spacer fabric structure resulted from post-buckling, torsion, shear, rotation and contacts of the spacer monofilaments as well as the contacts between the spacer monofilaments and outer layers. It was found from a parametric study that the spacer fabric structure made with smaller spacer yarn inclination angle, coarser spacer monofilaments and lower fabric thickness possesses higher compression resistance.
This part aims to investigate the effects of structural parameters and lamination on the impact f... more This part aims to investigate the effects of structural parameters and lamination on the impact force attenuation properties of warp-knitted spacer fabrics developed for impact protectors. A series of warp-knitted spacer fabrics was produced on a double-needle bar Raschel machine by varying their structural parameters including spacer monofilament inclination and fineness, fabric thickness, and outer layer structure. The effects of fabric structural parameters, impact energy levels, and laminated layers on the protective performance of the spacer fabrics were tested and analyzed based on the assessment of the peak transmitted force. The results showed that all the structural parameters significantly affect the impact force attenuation properties of the warp-knitted spacer fabrics. It was also found that lamination of the spacer fabrics can effectively improve the force attenuation performance. Three layers of the developed warp-knitted spacer fabrics in a total thickness of about 2.5 cm can meet the requirement of the transmitted force lower than 35 kN at an impact energy of 50 J according to the European Standard BS EN 1621-1:1998.
This paper presents an experimental study of the protective properties of warp-knitted spacer fab... more This paper presents an experimental study of the protective properties of warp-knitted spacer fabrics developed for protecting the human body on impact. A drop-weight impact tester was used to test the fabrics in a hemispherical form to simulate the use of impact protectors in real life. The study consists of two parts. The first part, presented in the current paper, focuses on the impact behavior of a typical spacer fabric impacted at different levels of energy. The analysis includes the impact process and the energy absorption and force attenuation properties of the spacer fabric. Frequency domain analysis is also used, to identify the different deformation and damage modes of the fabric under various levels of impact energy. The results show that the impact behavior of the fabric under impact in the hemispherical form is different from that in the planar form. The results also indicate that the curvature of the fabric can reduce energy absorption during the impact process and therefore reduce the force attenuation properties of the spacer fabric. This study provides a better understanding of the protective properties of spacer fabrics. The effect of fabric structural parameters and lamination on the protective properties of spacer fabrics under impact will be presented in Part II.
This paper presents a study of the impact compressive behavior of warp-knitted spacer fabrics dev... more This paper presents a study of the impact compressive behavior of warp-knitted spacer fabrics developed for human body protections. A series of warp-knitted spacer fabrics was produced on a double-needle bar Raschel warp knitting machine by varying their structural parameters, including spacer monofilament inclination and fineness, fabric thickness, and surface layer structure. A drop-weight impact tester was used to test these fabrics with predefined impact energy. The impact process of a typical spacer fabric was analyzed based on its impact contact force-displacement curve, energy absorbed-contact force curve and transmitted force-time curve. The effects of the structural parameters on the impact compressive behavior of the warp-knitted spacer fabrics were also discussed. The relationship between the peak transmitted force and peak contact force was established for these fabrics. The study shows that the warp-knitted spacer fabrics can be used as a type of effective material for human body protection due to their high energy absorption capacity and reduction of the contact peak force. The study also shows that all the structural parameters significantly affect the impact compressive behavior of the warp-knitted spacer fabrics in terms of peak contact force, peak transmitted force, and energy absorbed at different impact compressive stages. According to the results obtained, the warp-knitted spacer fabrics studied can reduce about 33.16% of the peak contact force.
This paper presents an investigation of the compression properties and air permeability of weft‐k... more This paper presents an investigation of the compression properties and air permeability of weft‐knitted spacer fabrics. Twenty spacer fabrics were knitted on a computerized flat knitting machine with different weft knit patterns, spacer yarns, and loop lengths (stitch cam settings). Their compression property and air permeability were tested with the Kawabata Evaluation System for Fabrics (KES‐F). The influences of different factors were discussed and compared. The results obtained provide some useful information for new spacer fabric development.
Cushioning materials generally absorb kinetic mechanical energy under compression actions at a re... more Cushioning materials generally absorb kinetic mechanical energy under compression actions at a relatively constant stress over a large range of displacement. However, cushioning materials widely used today are polyurethane (PU) foams with low moisture transmission. As a new class of three-dimensional textile structures, warp-knitted spacer fabrics not only have much better moisture transmission property than PU foams, but also have the similar cushioning performance if appropriate structural parameters are adopted. This paper reports an experimental study on the compression behavior of a series of warp-knitted fabrics made for cushioning applications. These fabrics were produced on a double-needle bar warp knitting machine of gauge 18 by varying different structural parameters including spacer yarn inclination angle and fineness, fabric thickness, and outer layer structure. Both the compression stress-strain curves and energy efficiency diagrams from the testing results were used to analyze the compression behavior of these fabrics and the effect of each structural parameter. The results indicate that warp-knitted spacer fabrics are an ideal class of the energy absorbers for cushioning applications and their energy-absorption capacity can easily be tailored to meet specific end-use requirements by simply varying their structural parameters with the help of efficiency diagrams.
Abstract: Compressibility of warp-knitted spacer fabrics is one of their important mechanical pro... more Abstract: Compressibility of warp-knitted spacer fabrics is one of their important mechanical properties with regard to many special applications such as body protection, cushion and mattresses. Due to specific structural features of the fabric and a non-linear mechanical behavior of monofilaments, the compression properties of this kind of fabrics are very complicated. Although several studies have been performed to investigate their compression behavior, its mechanism has not well been understood yet.
Auxetic polymeric materials are a special kind of materials that exhibit negative Poisson's ratio... more Auxetic polymeric materials are a special kind of materials that exhibit negative Poisson's ratio (NPR) effect. They get fatter when stretched and thinner when compressed. Auxetic behavior is a scaleindependent property which can be achieved at different structural levels from molecular to macroscopic levels. The internal structure of material plays an important role in obtaining auxetic effect.
This paper presents a comparative study on the mechanical properties of seven monofilaments of 0.... more This paper presents a comparative study on the mechanical properties of seven monofilaments of 0.12 mm diameter made with different polymeric materials including PET, PBT, PE, PP, and PA6 in order to assess their suitability for being spacer yarns for developing high-quality spacer fabrics. Their support capability and elasticity corresponding to fabric compression resistance and resilience, respectively, were evaluated by analyzing the tensile stress–strain relationships and residual strains of monofilaments subjected to cyclic tensile loading. Slack and taut heat setting on the monofilaments were also considered to select a proper heat setting method for their spacer fabrics. The mechanical properties of the monofilaments were explained by using the supramolecular structure information from X-ray diffraction and sonic orientation tests. The results showed that PET monofilaments have much higher moduli than the other monofilaments and possess better support capability as spacer yar...
Water transfer through porous textiles consists of two sequential processes: synchronous wicking–... more Water transfer through porous textiles consists of two sequential processes: synchronous wicking–evaporating and evaporating alone. In this work we set out to identify the main structural parameters affecting the water transfer process of cotton fabrics. Eight woven fabrics with different floats were produced. The fabrics were evaluated on a specially designed instrument capable of measuring the water loss through a vertical wicking process. Each test took 120 min, and two phases were defined: Phase I for the first 10 min and Phase II for the last 110 min according to wicking behavior transition. Principal components and multivariate statistical methods were utilized to analyze the data collected. The results showed that Phase I dominated the whole wicking–evaporating process, and the moisture transfer speed in this phase varied with fabric structure, whereas the moisture transfer speeds in Phase II were similar and constant regardless of fabric structure. In addition, fabric with m...
Three-dimensional mesh fabric is a special type of knitted spacer fabric with sandwich structure ... more Three-dimensional mesh fabric is a special type of knitted spacer fabric with sandwich structure consisting of two separate meshed multifilament outer layers linked together with a layer of spacer monofilaments. It has found wide applications in home textiles and automotive industry due to its good energy-absorbing performance and ventilation property. This article presents a comprehensive structural analysis on a mesh spacer fabric of thickness 10.3 mm in order to place a solid foundation to enhance the understanding of the structural features and mechanical behavior. The real geometric structure was reconstructed by scanning the fabric via Micro X-ray computed tomography. The spacer monofilaments and meshed outer layers were analyzed quantitatively based on the Micro X-ray computed tomography reconstruction. It was found that the spacer monofilaments are different in length, curvature, and torsion. The spacer monofilament lengths can be ranging from 9.43 to 10.77 mm. Their curvatu...
Textile strain sensors capable of monitoring human physiological signals and activities have grea... more Textile strain sensors capable of monitoring human physiological signals and activities have great potential in health monitoring and sports. Integrating them into apparel to be wearable, repeatable, and sensitive remains a great challenge, impeding their practical applications. This paper reports a fabric strain sensor that can be seamlessly integrated into various apparel under precise tension through industrial‐scale production. A conductive core‐sheath polyester/carbon black multifilament (CSPCF) produced on a melt spinning machine is wrapped onto a spandex yarn via a yarn covering machine to manufacture a stretchable double‐covered conductive yarn (DCCY). The fabric strain sensor is specially designed and automatically produced on an industrial knitting machine by precisely integrating the DCCY into an elastic fabric. The sensing principle is contact and separation between neighboring spiral CSPCFs by stretching an arched “rainbow spring” like DCCY embedded in the fabric. The sensor has a high sensitivity of 2% strain detection limit, excellent durability and repeatability for 10 000 cycles, and a wide sensing range of 60% strain, even in a wet state or after repeatedly washing, bending, or rubbing. Three wearable products, by seamlessly integrating the sensor, are demonstrated to effectively and quantitatively detect bending motions of finger, elbow, and knee. Integrating textile strain sensors into apparel is a great challenge but a prerequisite for practical applications. This work presents a fabric strain sensor with arched double‐covered conductive yarn detecting strains through “rainbow spring” like contact and separation of the spiral core‐sheath PET/carbon black multifilaments. A knitted sensing fingerstall by seamle
3D spacer fabrics are a type of sandwich structure consisting of two separate multifilament fabri... more 3D spacer fabrics are a type of sandwich structure consisting of two separate multifilament fabric outer layers linked together with a layer of spacer monofilaments. They have been widely used as energy absorbing materials and composite reinforcement. The microstructure features and compression behavior of a typical spacer fabric were investigated experimentally and numerically in this study. Eight unit cells with 64 spacer monofilaments were reconstructed from scanning of the fabric via Micro X-ray computed tomography (μCT). The geometric variations of the reconstructed spacer monofilaments were analyzed quantitatively. It was found that spacer monofilaments in different unit cells are different in length, curvature and torsion. A series of FE models based on different numbers and combinations of the identified unit cells were created. The FE simulation results showed that the geometric variations of spacer monofilaments have strong influence on the compression behavior , and the model with shorter length, lower curvature and torsion of spacer monofilaments has higher compression resistance. The compression resistance in the densification stage of the fabric increases with increasing the number of spacer monofilaments adopted due to more evident interactions among spacer yarns. This study provides an in-depth understanding on the compression behavior of spacer fabric.
The use of 3D knitted spacer fabrics made of polymeric fiber materials as vibration isolators is ... more The use of 3D knitted spacer fabrics made of polymeric fiber materials as vibration isolators is proposed in this study by considering their spacer monofilaments as Euler springs which have been proved to be excellent vibration isolators. Three types of spacer fabrics with different compression force–displacement characteristics were fabricated by varying monofilament diameter and fabric thickness. Their vibration transmissibility under harmonic vibration testing conditions was measured by an electromagnetic shaker. It is found that the resonant frequency and isolation frequency of these fabrics decrease with increasing acceleration level and load mass, and a thicker fabric has better vibration isolation performance due to its lower resonant and isolation frequencies. The study shows that 3D knitted spacer fabrics can be designed as good human vibration isolators without compromising their comfort.
This part presents a dynamic model for predicting the impact compressive responses of warp-knitte... more This part presents a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics
under various loading conditions using quasi-static compressive stress–strain data. The model was established based on a nonlinear mass-spring-damper system by considering spacer yarns as nonlinear springs with damping effect and representation of their stiffness by the constitutive model developed in Part I. Based on the dynamic model, the impact compressive responses of a typical warp-knitted spacer fabric was parametrically studied in terms of damping ratio, initial velocity, striker mass and contact area. The study indicates that damping can reduce the peak acceleration and peak displacement regardless of loading conditions, and the increase of the initial velocity can enhance the damping effect. Increasing initial velocity or striker mass while keeping the counterpart constant can increase the peak acceleration and peak displacement. However, at a constant kinetic energy, either increasing striker mass or decreasing initial velocity can reduce the peak acceleration, but the peak displacement keeps constant. The study also shows that an optimal size of the spacer fabric exists for achieving minimal peak acceleration under impact at a certain kinetic energy. Experimental validation by drop-weight impact tests demonstrates that the predictions of the dynamic model are in satisfactory agreement with the experimental results. Using the quasi-static compressive data from a simple test, this dynamic model can numerically simulate the full time-response of warp-knitted spacer fabrics under various impact conditions.
This paper presents a theoretical study of the compressive mechanics of warp-knitted spacer fabri... more This paper presents a theoretical study of the compressive mechanics of warp-knitted spacer fabrics. The first part, as
presented in the current paper, focuses on the establishment of a constitutive model that can give accurate compressive stress–strain relationships of warp-knitted spacer fabrics. Based on the analysis of three existing models for polymeric or metallic foams, a constitutive model consisting of seven parameters was firstly proposed for spacer fabrics. The effect of each parameter on the regressive stress–strain curves was then parametrically studied. Experimental validation was finally conducted by using 12 warp-knitted spacer fabrics produced with different spacer monofilament diameters and inclination angles, fabric thicknesses, and outer layer structures to identify the physical sense of the parameters. The analysis has showed that an excellent agreement exists between the regressive and experimental results, and all seven parameters have a quantitative effect on a particular phase of the resultant compressive stress–strain curves of warp-knitted spacer fabrics. The change of each parameter makes a clear physical sense on the stress–strain curve. Therefore, the proposed constitutive model can be used as a useful tool to engineer the cushioning properties of warp-knitted spacer fabrics. The adoption of the constitutive model to develop a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics under various loading conditions will be presented in Part II.
International Journal of Mechanical Sciences 94-95(2015)244–259, Mar 9, 2015
3D finite element (FE) analysis was conducted to investigate the mechanical behaviour of a typica... more 3D finite element (FE) analysis was conducted to investigate the mechanical behaviour of a typical 3D spacer fabric structure under compression in terms of its structure feature and mechanical properties of its components. A spacer fabric consists of two separate outer layers joined together with spacer monofilaments. Six FE models with different constraints on the spacer monofilaments and outer layer thicknesses were created using the precise geometry of a unit cell from Micro X-ray computed tomography (μCT) scanning by fully considering the yarn interactions among all the fabric components and material's nonlinearity. A FE model which could give a satisfactory prediction of the compression load–displacement relationship of the fabric was employed to identify the compression mechanism. It was confirmed from the simulation that the nonlinear compression behaviour of the 3D spacer fabric structure resulted from post-buckling, torsion, shear, rotation and contacts of the spacer monofilaments as well as the contacts between the spacer monofilaments and outer layers. It was found from a parametric study that the spacer fabric structure made with smaller spacer yarn inclination angle, coarser spacer monofilaments and lower fabric thickness possesses higher compression resistance.
This part aims to investigate the effects of structural parameters and lamination on the impact f... more This part aims to investigate the effects of structural parameters and lamination on the impact force attenuation properties of warp-knitted spacer fabrics developed for impact protectors. A series of warp-knitted spacer fabrics was produced on a double-needle bar Raschel machine by varying their structural parameters including spacer monofilament inclination and fineness, fabric thickness, and outer layer structure. The effects of fabric structural parameters, impact energy levels, and laminated layers on the protective performance of the spacer fabrics were tested and analyzed based on the assessment of the peak transmitted force. The results showed that all the structural parameters significantly affect the impact force attenuation properties of the warp-knitted spacer fabrics. It was also found that lamination of the spacer fabrics can effectively improve the force attenuation performance. Three layers of the developed warp-knitted spacer fabrics in a total thickness of about 2.5 cm can meet the requirement of the transmitted force lower than 35 kN at an impact energy of 50 J according to the European Standard BS EN 1621-1:1998.
This paper presents an experimental study of the protective properties of warp-knitted spacer fab... more This paper presents an experimental study of the protective properties of warp-knitted spacer fabrics developed for protecting the human body on impact. A drop-weight impact tester was used to test the fabrics in a hemispherical form to simulate the use of impact protectors in real life. The study consists of two parts. The first part, presented in the current paper, focuses on the impact behavior of a typical spacer fabric impacted at different levels of energy. The analysis includes the impact process and the energy absorption and force attenuation properties of the spacer fabric. Frequency domain analysis is also used, to identify the different deformation and damage modes of the fabric under various levels of impact energy. The results show that the impact behavior of the fabric under impact in the hemispherical form is different from that in the planar form. The results also indicate that the curvature of the fabric can reduce energy absorption during the impact process and therefore reduce the force attenuation properties of the spacer fabric. This study provides a better understanding of the protective properties of spacer fabrics. The effect of fabric structural parameters and lamination on the protective properties of spacer fabrics under impact will be presented in Part II.
This paper presents a study of the impact compressive behavior of warp-knitted spacer fabrics dev... more This paper presents a study of the impact compressive behavior of warp-knitted spacer fabrics developed for human body protections. A series of warp-knitted spacer fabrics was produced on a double-needle bar Raschel warp knitting machine by varying their structural parameters, including spacer monofilament inclination and fineness, fabric thickness, and surface layer structure. A drop-weight impact tester was used to test these fabrics with predefined impact energy. The impact process of a typical spacer fabric was analyzed based on its impact contact force-displacement curve, energy absorbed-contact force curve and transmitted force-time curve. The effects of the structural parameters on the impact compressive behavior of the warp-knitted spacer fabrics were also discussed. The relationship between the peak transmitted force and peak contact force was established for these fabrics. The study shows that the warp-knitted spacer fabrics can be used as a type of effective material for human body protection due to their high energy absorption capacity and reduction of the contact peak force. The study also shows that all the structural parameters significantly affect the impact compressive behavior of the warp-knitted spacer fabrics in terms of peak contact force, peak transmitted force, and energy absorbed at different impact compressive stages. According to the results obtained, the warp-knitted spacer fabrics studied can reduce about 33.16% of the peak contact force.
This paper presents an investigation of the compression properties and air permeability of weft‐k... more This paper presents an investigation of the compression properties and air permeability of weft‐knitted spacer fabrics. Twenty spacer fabrics were knitted on a computerized flat knitting machine with different weft knit patterns, spacer yarns, and loop lengths (stitch cam settings). Their compression property and air permeability were tested with the Kawabata Evaluation System for Fabrics (KES‐F). The influences of different factors were discussed and compared. The results obtained provide some useful information for new spacer fabric development.
Cushioning materials generally absorb kinetic mechanical energy under compression actions at a re... more Cushioning materials generally absorb kinetic mechanical energy under compression actions at a relatively constant stress over a large range of displacement. However, cushioning materials widely used today are polyurethane (PU) foams with low moisture transmission. As a new class of three-dimensional textile structures, warp-knitted spacer fabrics not only have much better moisture transmission property than PU foams, but also have the similar cushioning performance if appropriate structural parameters are adopted. This paper reports an experimental study on the compression behavior of a series of warp-knitted fabrics made for cushioning applications. These fabrics were produced on a double-needle bar warp knitting machine of gauge 18 by varying different structural parameters including spacer yarn inclination angle and fineness, fabric thickness, and outer layer structure. Both the compression stress-strain curves and energy efficiency diagrams from the testing results were used to analyze the compression behavior of these fabrics and the effect of each structural parameter. The results indicate that warp-knitted spacer fabrics are an ideal class of the energy absorbers for cushioning applications and their energy-absorption capacity can easily be tailored to meet specific end-use requirements by simply varying their structural parameters with the help of efficiency diagrams.
Abstract: Compressibility of warp-knitted spacer fabrics is one of their important mechanical pro... more Abstract: Compressibility of warp-knitted spacer fabrics is one of their important mechanical properties with regard to many special applications such as body protection, cushion and mattresses. Due to specific structural features of the fabric and a non-linear mechanical behavior of monofilaments, the compression properties of this kind of fabrics are very complicated. Although several studies have been performed to investigate their compression behavior, its mechanism has not well been understood yet.
Auxetic polymeric materials are a special kind of materials that exhibit negative Poisson's ratio... more Auxetic polymeric materials are a special kind of materials that exhibit negative Poisson's ratio (NPR) effect. They get fatter when stretched and thinner when compressed. Auxetic behavior is a scaleindependent property which can be achieved at different structural levels from molecular to macroscopic levels. The internal structure of material plays an important role in obtaining auxetic effect.
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under various loading conditions using quasi-static compressive stress–strain data. The model was established based on a nonlinear mass-spring-damper system by considering spacer yarns as nonlinear springs with damping effect and representation of their stiffness by the constitutive model developed in Part I. Based on the dynamic model, the impact compressive responses of a typical warp-knitted spacer fabric was parametrically studied in terms of damping ratio, initial velocity, striker mass and contact area. The study indicates that damping can reduce the peak acceleration and peak displacement regardless of loading conditions, and the increase of the initial velocity can enhance the damping effect. Increasing initial velocity or striker mass while keeping the counterpart constant can increase the peak acceleration and peak displacement. However, at a constant kinetic energy, either increasing striker mass or decreasing initial velocity can reduce the peak acceleration, but the peak displacement keeps constant. The study also shows that an optimal size of the spacer fabric exists for achieving minimal peak acceleration under impact at a certain kinetic energy. Experimental validation by drop-weight impact tests demonstrates that the predictions of the dynamic model are in satisfactory agreement with the experimental results. Using the quasi-static compressive data from a simple test, this dynamic model can numerically simulate the full time-response of warp-knitted spacer fabrics under various impact conditions.
presented in the current paper, focuses on the establishment of a constitutive model that can give accurate compressive stress–strain relationships of warp-knitted spacer fabrics. Based on the analysis of three existing models for polymeric or metallic foams, a constitutive model consisting of seven parameters was firstly proposed for spacer fabrics. The effect of each parameter on the regressive stress–strain curves was then parametrically studied. Experimental validation was finally conducted by using 12 warp-knitted spacer fabrics produced with different spacer monofilament diameters and inclination angles, fabric thicknesses, and outer layer structures to identify the physical sense of the parameters. The analysis has showed that an excellent agreement exists between the regressive and experimental results, and all seven parameters have a quantitative effect on a particular phase of the resultant compressive stress–strain curves of warp-knitted spacer fabrics. The change of each parameter makes a clear physical sense on the stress–strain curve. Therefore, the proposed constitutive model can be used as a useful tool to engineer the cushioning properties of warp-knitted spacer fabrics. The adoption of the constitutive model to develop a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics under various loading conditions will be presented in Part II.
under various loading conditions using quasi-static compressive stress–strain data. The model was established based on a nonlinear mass-spring-damper system by considering spacer yarns as nonlinear springs with damping effect and representation of their stiffness by the constitutive model developed in Part I. Based on the dynamic model, the impact compressive responses of a typical warp-knitted spacer fabric was parametrically studied in terms of damping ratio, initial velocity, striker mass and contact area. The study indicates that damping can reduce the peak acceleration and peak displacement regardless of loading conditions, and the increase of the initial velocity can enhance the damping effect. Increasing initial velocity or striker mass while keeping the counterpart constant can increase the peak acceleration and peak displacement. However, at a constant kinetic energy, either increasing striker mass or decreasing initial velocity can reduce the peak acceleration, but the peak displacement keeps constant. The study also shows that an optimal size of the spacer fabric exists for achieving minimal peak acceleration under impact at a certain kinetic energy. Experimental validation by drop-weight impact tests demonstrates that the predictions of the dynamic model are in satisfactory agreement with the experimental results. Using the quasi-static compressive data from a simple test, this dynamic model can numerically simulate the full time-response of warp-knitted spacer fabrics under various impact conditions.
presented in the current paper, focuses on the establishment of a constitutive model that can give accurate compressive stress–strain relationships of warp-knitted spacer fabrics. Based on the analysis of three existing models for polymeric or metallic foams, a constitutive model consisting of seven parameters was firstly proposed for spacer fabrics. The effect of each parameter on the regressive stress–strain curves was then parametrically studied. Experimental validation was finally conducted by using 12 warp-knitted spacer fabrics produced with different spacer monofilament diameters and inclination angles, fabric thicknesses, and outer layer structures to identify the physical sense of the parameters. The analysis has showed that an excellent agreement exists between the regressive and experimental results, and all seven parameters have a quantitative effect on a particular phase of the resultant compressive stress–strain curves of warp-knitted spacer fabrics. The change of each parameter makes a clear physical sense on the stress–strain curve. Therefore, the proposed constitutive model can be used as a useful tool to engineer the cushioning properties of warp-knitted spacer fabrics. The adoption of the constitutive model to develop a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics under various loading conditions will be presented in Part II.