Vibrometer

There is a pressing need to develop effective techniques for structural health monitoring, so that the safety and integrity of the composite structures can be improved. The main objective of this study is to evaluate dynamics-based damage detection techniques for composite laminated plates using smart piezoelectric materials and modern instrumentation like scanning laser vibrometer (SLV). The study comprises of testing an E-glass/epoxy composite plate with an embedded delamination using two different actuator–sensor systems: (1) SLV with PZT (lead–zirconate–titanate) actuators (PZT-SLV), and (2) polyvinylidenefluoride (PVDF) sensors with PZT actuators (PZT-PVDF). The numerical finite element (FE) analysis is also performed to complement the damage detection. The experimental and numerical curvature mode shapes are primarily used to detect the presence, location, and size of the delamination. Three relatively new damage detection algorithms (i.e., simplified gapped smoothing method (GSM), generalized fractal dimension (GFD), and strain energy method (SEM)) are employed to analyze the experimental and numerical curvature mode shape data and uniform load surface (ULS) curvatures. From the damage detection outcomes, it is observed that the PZT-SLV system proves to be more convenient and effective, and it is capable of scanning a large number of points over the entire plate specimens; while the PZT-PVDF system, in which the curvature mode shapes are directly acquired, exhibits good sensitivity to damage. The damage detection algorithms like GSM, GFD and SEM based on the utilization of three consecutive mode curvatures (modes 3–5) and resulting ULS curvature successfully identify the presence, location, and relative size of delamination in the composite plate.

Machining and measuring operations are invariably accompanied by relative vibration between work piece and tool. The effect of vibration is excessive stresses, undesirable noise, looseness of part and partial or complete failure of parts. In this work the cutting tool vibration will be measured by using digital Vibrometer, which can measure displacement velocity, acceleration and frequency. The sensor will be attached with the tool post for sensing the vibration tool during turning operation. Vibration also increases in the cutting tool due to whiling of the job mounted between two stocks of lathe machine. With the increasing feed rate, the surface roughness of work will increase. The feed rate can be considered as a main cutting factor in the machining operation. The mildsteel material will be used for collecting data at various cutting parameters like depth of cut, speed, feed rate etc. on the completion of experimental work data will be analysing using MATLAB. By doing the same we will be able to predict behaviour for the system under any operating cutting parameters.

Recently, scanning laser Doppler vibrometry experiments have been conducted in order to identify structural faults in frescoes at the US Capitol. In these experiments, the artwork is subjected to force excitations over a range of frequencies and a laser vibrometer is used to measure the velocity response of the structure over an array of spatial locations. At each frequency, a two-dimensional spatial image of the force-velocity transfer function is obtained. Spatial locations that consistently exhibit large responses are indicative of potential regions of delamination. In this paper the use of proper orthogonal decomposition, also known as principle component analysis, to identify coherent features in the structural response and obtain a succinct representation of the data is described. It is shown that, for the fresco studied in this paper, the response can be characterized in terms of only a few proper orthogonal decomposition modes. Unfortunately, these modes are corrupted by spatially varying noise. This noise is a result of surface irregularities that affect the direction in which the incident laser beam is reflected, which in turn corrupts the measured response at those locations. Therefore, the use of spatial filtering techniques is also explored for removing this "speckle noise" from the measured force-velocity transfer functions prior to performing the proper orthogonal decomposition analysis. Wavelets are particularly well suited for this application because they decompose images into functions that are localized in the spatial and frequency domains. In this paper, several wavelet bases with differing properties are used to filter the scanning laser Doppler vibrometry images. In addition, wavenumber filters, which essentially act as low-pass filters, are also employed. While the results do not definitively show which filtering technique is most effective for this application, it is clear that both wavelet processing and wavenumber filtering can reduce speckle noise while retaining the salient physical features in the image data. Therefore, it is demonstrated that proper orthogonal decomposition analysis coupled with spatial filtering is an effective tool for analyzing scanning laser Doppler vibrometry data in fault detection applications.

ABSTRACT The radial error motion of a machine tool cutter/spindle system is critical to the dimensional accuracy of the parts to be machined. The spindle's radial error motions can be measured by mounting a sphere target onto the spindle as a reference. A set of sensors is used to measure displacements of the reference sphere in various directions to determine spindle error motions. This measurement technique can be reliably carried out when the spindle is at rest or at low rotational speeds. However, at very high speeds, the reference sphere must be carefully centered and balanced to avoid introducing additional error motions. In addition, the sensors must be held with very rigid mounts in order to avoid measurement errors caused by vibrations. For high-speed end milling spindles, the spindle is operated with a cutter. The cutter must be removed when mounting a reference sphere. Because the cutter itself can introduce errors due to centering and unbalancing effects, the error motions measured by the reference sphere method do not include the error caused by the cutter. This paper introduces a new and practical method to provide an indicator of the radial error of a motorized end-milling cutter/spindle system at very high speed rotations without the need of a reference sphere. This indicator of the radial error is based on the size of the cutting marks produced by the end mill, which is attached to the spindle. The cutting marks are circular, and their diameters are related to the radial error of the cutter/spindle system. Quantitative precision analysis was carried out to confirm the accuracy and repeatability of this new measurement technique. This technique has been implemented in order to determine the effects of the spindle speed, the level of unbalanced mass, and the spindle stiffness on the cutter/spindle's radial error. The results reveal that the centrifugal force generated by the unbalanced mass is the main factor causing the increase in radial error. One way to compensate for the effect of unbalanced mass is to increase the spindle stiffness. Experimental results confirm that a higher front bearing preload can render the spindle stiffer, thus reducing the radial error of the cutter/spindle system. Finally, it should be pointed out that the proposed cutting mark measurement cannot replace the sphere method because it cannot provide time-resolved or angle-resolved information as those obtained from polar charts. However, the proposed cutting mark measurement can provide the characterization of the spindle with the cutter attached. As a result, both methods can complement each other to provide a more complete picture of the behavior of the cutter/spindle system at high speeds.

In this paper a measurement method for the analysis of the structural behaviour of heart valves is presented by the use of the thermoelasticity and laser Doppler vibrometry. A special experimental test bench has been realized with the purpose to fix the body of the valve and to excite the parts of remarkable importance from the structural point of view by means of a shaker. The vibrational measurements have been adopted as boundary condition for the FEM simulations and the relative maps in terms of stress have subsequently been validate through the employment of the thermoelasticity.

Structural Health Monitoring (SHM) is becoming an increasingly important tool for the maintenance, safety and integrity of aerospace structural systems. Immune to electromagnetic interference, Fiber Bragg Grating (FBG) optical sensor matrices are light-weight and multiplexable, allowing many sensors on a single fiber to be integrated into smart structures. Highly sensitive to minute strains, they can facilitate maximum SHM functionality, with minimum weight and size. Consequently, these optical systems, in conjunction with advanced damage characterization algorithms, are expected to play an increasing role in extending the life and reducing costs of new generations of structures and airframes. In this paper, we discuss the development of both hardware and algorithms to detect, locate and quantify delamination in composite laminated beam structures. We present an integrated SHM system including (a) the capability of interrogating over 50 FBG sensors simultaneously with sub-picometer resolution at over 50 kHz, (b) an FBG-sensor/piezo-actuator matrix smart skin design and methodology, and (c) damage detection location and quantification algorithms based on mode shape or other relevant advanced algorithmic-based damage diagnosis and prognosis techniques. Comparison with other SHM systems (e.g., based on piezo-electric (PVDF) and Scanning Laser Vibrometer sensors) demonstrates better signal-to-noise and damage detection for our FBG system.

The paper presents guided elastic waves and their identification and damage interaction in a CFRP plate. After the excitation of a fiber transducer, different elastic waves emerge in a plate. By using specially developed 3D laser scanning software it was possible to specify the different wave modes. These wave modes have been described concerning their propagating velocities and different motion components. The interaction of different wave modes with introduced impact damage (7J) is shown. In some experiments, it was proven that impact locations can be derived from the detected Lamb waves. This work is continued to develop structural health monitoring systems (SHM) for selected aircraft components (e. g. stringer elements, panels).