Dynamic Photoelastic Method Research Articles

A Study on the Development of the Dynamic Photoelastic Hybrid Method for Two Dissimilar Isotropic Bi-Materials

When the interfacial crack of two dissimilar isotropic bi-materials is propagated with constant velocity along the interface, stress and displacement components are derived in this research. The dynamic photoelastic experimental hybrid method for bimaterial is introduced. It is assured that stress components and dynamic photoelastic hybrid method developed in this research are valid. Separating method of stress component is introduced from only dynamic photoelastic fringe patterns. Crack propagating velocity of interfacial crack is 80∼85% (in case of aluminum, 24.3∼25.9%) of Rayleigh wave velocity of epoxy resin. The near-field stress components of crack-tip are similar with those of pure isotropic material under static or dynamic loading, but very near-field stress components of crack-tip are different from those.

Dynamic mixed mode crack propagation behavior of structural bonded joints

The stress field around the dynamically propagating interface crack tip under a remote mixed mode loading condition has been studied with the aid of dynamic photoelastic method. The variation of stress field around the dynamic interface crack tip is photographed by using the Cranz-Shardin type camera having 106 fps rate. The dynamically propagating crack velocities and the shapes of isochromatic fringe loops are characterized for varying mixed load conditions in double cantilever beam (DCB) specimens. The dynamic interface crack tip complex stress intensity factors,K1 andK2, determined by a hybrid-experimental method are found to increase as the load mixture ratio of y/x (vertical/horizontal) values. Furthermore, it is found that the dynamically propagating interface crack velocities are highly dependent upon the varying mixed mode loading conditions and that the velocities are significantly small compared to those under the mode I impact loading conditions obtained by Shukla (Singh & Shukla, 1996a, b) and Rosakis (Rosakis et al., 1998) in the USA.

Dynamic Mixed Mode Crack Propagation Behavior of Structural Bonded Joints

The stress field around the dynamically propagating interface crack tip under a remote mixed mode loading condition has been studied with the aid of dynamic photoelastic method. The variation of stress field around the dynamic interface crack tip is photographed by using the Cranz-Shardin type camera having 106 fps rate. The dynamically propagating crack velocities and the shapes of isochromatic fringe loops are characterized for varying mixed load conditions in double cantilever beam (DCB) specimens. The dynamic interface crack tip complex stress intensity factors,K1 andK2, determined by a hybrid-experimental method are found to increase as the load mixture ratio of y/x (vertical/horizontal) values. Furthermore, it is found that the dynamically propagating interface crack velocities are highly dependent upon the varying mixed mode loading conditions and that the velocities are significantly small compared to those under the mode I impact loading conditions obtained by Shukla (Singh & Shukla, 1996a, b) and Rosakis (Rosakis et al., 1998) in the USA.

A Study on the Development of the Dynamic Photoelastic Hybrid Method for Isotropic Material

In this paper, dynamic photoelastic hybrid method is developed and its validity is certified. The dynamic photoelastic hybrid method can be used on the obtaining of dynamic stress intensity factors and dynamic stress components. The effect of crack length on the dynamic stress intensity factors is less than those on the static stress intensity factors. When structures are under the dynamic mixed mode load, dynamic stress intensity factor of mode I is almost produced. Dynamic loading device manufactured in this research can be used on the research of dynamic behavior when mechanical resonance is produced and when crack is propagated with the constant velocity

Experimental study on the characteristic of the NS-GT cut quartz crystal resonator oscillating in the sub-resonant frequency

We previously reported that the dynamic photo-elastic method was a very effective measuring technique for the stress distribution of vibrating quartz crystal resonators. The existence of a twisted asymmetrical vibration mode has been verified experimentally when the NS-GT cut quartz crystal resonator was vibrating in the main resonant frequency (MRF). A MRF and a sub-resonant frequency (SRF) of the NS-GT cut quartz resonator were defined as follows. If a mechanical standing wave was in the x' or y' direction of the resonator, the former was MRF vibration and the latter was SRF vibration, respectively. In this paper, stress distributions of two samples of the NS-GT cut quartz crystal resonator, one of which had a thickness of 80 mum and the other 150 mum, were measured by the dynamic photo-elastic method when the resonators were vibrating in each SRF. Thereafter, vibration modes of those resonators were estimated by the experimental data of stress distributions. We find that the vibration mode of the 80-mum resonator had a simple mechanical standing wave on the y' direction and the vibration mode of the 150-mum resonator was combined with a shearing mode in the SRF vibration. From the experiment, we decided that vibration modes of the NS-GT cut quartz crystal resonator were composed of the longitudinal stress T(3)' belonging to the z' direction of the plate and of the shearing stress T(5)' when the plate thickness was thickened and the resonator was oscillating in the SRF.

Relationship between the Duration of Stress Pulse and Dynamic Stress Concentration in a Strip Plate with Fillet of Photoelastic Material.

The purpose of this study is to clarify the dynamic behavior of stress waves in strip plates with fillets experimentally. The reflection coefficient, with corresponds to the changes in the duration of the incident pulse and the fillet shape, has been obtained by the strain gauge method. The relationship between the duration of incident stress waves to the fillet and the dynamic stress concentration factor is obtained by a dynamic photoelastic method. An interaction of the incident wave and the reflected wave takes place at the fillet. Depending on the fillet shape, the dynamic stress concentration factor becomes 10-70% higher than the static stress concentration factor for incident waves. The relationship between the duration of stress pulse and the dynamic stress concentration factor has also been obtained.

Dynamic Stress Concentration in Strip Plate with Fillet.

A method of measuring the maximum dynamic stress concentration factor αDmax in a fillet has not yet established. The reflection and transmission of stress wave during the propagation through a fillet result in complex stress states. We propose a new method for analyzing the maximum dynamic stress concentration factor αDmax in a fillet utilizing the stress concentration factor αS and the reflection coefficient A obtained by a strain gauge on the incident strip plate. In this experiment, a square wave(a stress wave with a plateau of constant stress for long duration)is used. A strain gauge measures the reflection coefficient A. The factor αDmax in the fillet is analyzed using a dynamic photoelastic method. It is confirmed that αDmax is approximated by the following equation:αexDmax=(1+A)αS. As a result, the maximum dynamic stress concentration factor is obtained experimentally using the static stress concentration factor and the reflection coefficient.

Application of the photo-elastic method to measurement of dynamic stress distribution for NS-GT cut quartz crystal resonators

NS-GT cut quartz crystal resonators are widely used as a frequency standard element in consumer products and communication equipment. The vibration mode of the resonators was analyzed by the finite element method (FEM) because they have a complicated shape. As a result, an asymmetrical vibration mode at the main resonant frequency has been obtained by the FEM simulation. But, it is necessary to confirm the asymmetrical vibration mode experimentally because it is just a simulation. In this paper, stress distributions of the NS-GT cut quartz crystal resonators are measured experimentally by using a dynamic photo-elastic method when the resonators are vibrating in the resonant frequency; thereafter, vibration modes of the NS-GT cut resonators are estimated with the experimental data of the stress distributions. This experiment for the NS-GT cut quartz crystal resonators exposes the existence of a twisted asymmetrical vibration mode at the main resonant frequency, with the magnitude of the twisted vibration in proportion to thickness of the resonators.

Dynamic Stress Concentration in a Strip Plate with Fillet.

A method of measuring the dynamic stress concentration factor αDmax in a fillet has not yet established. The reflection and transmission of stress wave during the propagation through a fillet result in complex stress states. We propose a new method for analyzing the dynamic stress concentration factor αDmax in a fillet utilizing the stress concentration factor αs and the reflection coefficient A obtained by a strain gauge on the incident strip plate. In this experiment, a square wave (a stress wave with a plateau of constant stress for long duration) is used. A strain gauge measures the reflection coefficient A. The factor αDmax in the fillet is analyzed using a dynamic photoelastic method. It is confirmed that αDmax is approximated by the following equation : αexDmax=(1+A)αs As a result, the dynamic stress concentration factor is obtained experimentally using the static stress concentration factor and the reflection coefficient.

Evaluation of aseismic integrity in the HTTR core-bottom structure V. On the static and dynamic behavior of graphitic HTTR key-keyway structures

The graphite components in high temperature gas-cooled reactors are connected to each other through a key-keyway structure that has gaps between the key and the keyway to accomodate thermal expansion. Because a dynamic load concentrates on the key-keyway structure during earthquakes, it is considered to be a crucial element for assessing the integrity of the graphite components. A combination of experiments and analyses was employed to investigate the dynamic behavior of the key-keyway structure, i.e. the equivalent stiffness associated with vibrational characteristics of the graphite components and the stress distribution under dynamic loading. The experiments were performed using a graphite scale model and a dynamic photo-elastic method. The analysis was carried out using the finite element method (FEM) code Abaqus, taking account of the contact between the key and the keyway. The following conclusions were derived. (1) The equivalent stiffness of the key-keyway structure shows nonlinearity, owing to the contact deformation. (2) The equivalent stiffness evaluated by the FEM analysis, taking account of the non-inear contact deformation, is applicable for predicting the vibrational characteristics of ky-keyway structure. (3) The stress concentration under dynamic loading is lower than or nearly equal to that under static loading. The maximum stress concentration of the seismic load can be sufficiently evaluated under static loading conditions.

Dynamic photoelasticity method using three-layer striker and its application to key/keyway structure : Journal of JSNDI, vol. 42, no. 11 (November 1993) p. 617 Inoue, Atsushi; Takeishi, Hiroyuku; Futakawa, Masatoshi

Dynamic photoelasticity method using three-layer striker and its application to key/keyway structure : Journal of JSNDI, vol. 42, no. 11 (November 1993) p. 617 Inoue, Atsushi; Takeishi, Hiroyuku; Futakawa, Masatoshi

Crack growth kinetics under impulse loading

The dynamic photoelasticity method has been used to study the effect of the acting wave, and the size and orientation of the incident wave front on crack growth kinetics (under short-term pulse loading). It has also been used to study the mechanism of dynamic stress formation at the crack tip. It has been shown that when compression or tensile waves are incident on the crack at an angle of 0<α<80 and 100<α<180°, the field of dynamic stress which arises is determined by the transverse shear strain while at an angle of 90±10°, stress formation is caused by strain tearing. When transverse waves act on a crack, there is a considerable amount of stress concentration at the crack tip irrespective of the incident angle. It has been established that one-, two-, or threefold crack growth occurs depending on the pulses and the crack depth.

Influence of singularity dominated zone for propagating cracks in finite size specimens

The singularity dominated zones for straight as well as curved cracks propagating in finite size specimens were determined experimentally by using the optical method of dynamic photoelasticity using the near-field stress equations. Experimental data was carefully analyzed using improved numerical schemes to get the complete stress field around the propagating crack. This stress field was critically examined to evaluate the size of singularity dominated zones for cracks propagating in straight as well as curved paths. For this purpose, the exact solution was compared with the singular solution using stress components σ x, σ y, τ xy and the maximum shear stress τ max as a criterion respectively. For straight cracks where the stress field is symmetric about the crack path, the singularity dominated zones can be determined by using any one of the stresses. However, for a curved crack, the zones were unsymmetric. This study shows that σ y , the crack opening stress, yields the best result for characterizing the singularity dominated zone around a running crack tip.

Dynamic photoelastic studies of wave propagation in granular media

The optical method of dynamic photoelasticity is used to visualize the load transfer profiles due to explosive loading in granular aggregates. The granular media are simulated by using arrays of disks fabricated from a brittle polyester material—Homalite 100. Attention is focused on the effect of microstructure or the geometrical packing of the grains on the wave propagation phenomena. The experimental data are analyzed to obtain the stress wave attenuation, wave velocities and contact stresses as a function of time along various directions in the assembly of grains. Dynamic load transfer functions are developed to predict dynamic contact loads in any systematic or random assembly of grains for any given loading. The predicted results are compared with the experimental data. The effect of local inhomogeneities on the wave propagation phenomena is also shown.

New optically sensitive polymer materials for the dynamic photoelasticity method having different moduli

New optically sensitive polymer materials for the dynamic photoelasticity method having different moduli

Experimental and computational modeling of wave propagation in granular materials

A hybrid experimental-computational study has been conducted in order to determine the propagational characteristics of mechanical waves in granular materials. The experimental investigation has used the method of dynamic photoelasticity to collect photographic data which provide information on the wave speeds, integranular contact loadings, and wave-spreading characteristics. The computational study employed the use of the distinct-element method whereby the motion of each granule in the material is modeled by rigid-body dynamics assuming each particle interaction has particular frictionless stiffness and damping forces. The experimental results provide special dynamic material constants necessary for the computational modeling, and they also provide data for comparison purposes. Results from the experimental and computational studies compare well with each other and indicate that local microstructure plays an important role in the wave propagation through such materials.

面内集中荷重を受ける円輪の動的挙動

Dynamic response of circular rings with various diameter ratios to inplane concentrated impact was examined. The electromagnetic induction method was employed for the generation of impulse because of its good reproducibility and controllability of amplitude. The dynamic photoelastic method and semiconductor strain gauges were used for the measurement of the stress wave propagation through the circular ring.It was confirmed that compressive stress waves propagated into the circular ring transformed to tensile stress waves at the position of conflux stress waves. The stress concentration ratio in the circular ring under the present condition was 12-13% higher than that of the case subjected to diametrically opposite external concentrated static load. Moreover, when excessive stress waves were generated in the circular ring, the appearance of a group of cracks was observed.

Dynamic fracture behavior of anisotropic plates with an inclined edge crack.

This paper is concerned with the dynamic fracture behavior of anisotropic plates with a mixed-mode crack by means of the dynamic photoelastic method using a high speed image converter camera. A rectangular plate is made of fiber reinforced plastic with an inclined edge crack parallel to the fiber direction. According to examinations, the static stress intensity factor and the dynamic stress intensity factor of the tensile stress was required, and was compared with the results for an isotropic plate by changing the fiber direction, and with an increasing crack length.

Dynamic stress analysis of plates of different kinds material.

Structures of machine parts subjected impact load often suffer unexpected damage, which is remarkably different from the observed in static cases. Generally, the reflection and interferference of stress-wave play an important role in dynamic cases, and it is desirable to study the time variation of the stress distribution, and especially the value of dynamic stress concentration factors around the boundaries of different kinds of materials. Hence, we analyzed stress propagation and dynamic stress concentration phenomena around the boundary of different kinds of materials in a plate by utilizing the strain gage method, the dynamic photoelastic method and also the finite element method. We found that two-dimensional dynamic stress concentration factors obtained by the present three methods are in general agreement and if the ratio of E2 (young's modulus for the different materials)/E1 (young's modulus for the matrix) is small, the dynamic stress concentration factor is small, but the position of maximum stress occurs at the circular bounday of the matrix. On the other hand, if the ratio of E2/E1 is large, the dynamic stress concentration factor is large, and the position of maximum stress occurs at the boundary of the circular hole in various types of materials.

Dynamic stress-concentration effects on stress waves in composite models with different fiber-end geometries

The stress-concentration effect of fiber-end geometries on the propagating stress waves in composite models was investigated by the dynamic photoelastic method. Aluminum fibers with rectangular, semicircular, v- and wedgeshape ends simulating such materials as reinforced concrete and fiber-bundle-reinforced composites were cast in epoxy resin to form the models. Impact was applied by the bullet of a rilfe. The effects of the reinforced rod or fiber-bundle ends on the dynamic birefringent patterns were analyzed by comparing the fringe patterns at the same locations in a plain model of identical contour under the same loading conditions.