Dynamic Photoelasticity Research Articles

계면에 존재하는 구멍의 모양이 동적 계면균열전파에 미치는 영향

The dynamic photoelasticity with the aid or Cranz-Shardin type high speed camera system is utilized to record the dynamically propagating behavior of the interrace crack. This paper investigates the effects of the hole (existed along the path of the crack propagation) shape on the dynamic interface crack propagation behavior by comparing the experimental isochromatic fringes to the theoretical stress fields.

Digital Photoelasticity: Advanced Techniques and Applications

Digital Photoelasticity: Advanced Techniques and Applications

Optical methods in fault dynamics

The Rayleigh pulse interaction with a pre-stressed, partially contacting interface between similar and dissimilar materials is investigated experimentally as well as numerically. This study is intended to obtain an improved understanding of the interface (fault) dynamics during the earthquake rupture process. Using dynamic photoelasticity in conjunction with high-speed cinematography, snapshots of time-dependent isochromatic fringe patterns associated with Rayleigh pulse–interface interaction are experimentally recorded. It is shown that interface slip (instability) can be triggered dynamically by a pulse which propagates along the interface at the Rayleigh wave speed. For the numerical investigation, the finite difference wave simulator SWIFD is used for solving the problem under different combinations of contacting materials. The effect of acoustic impedance ratio of the two contacting materials on the wave patterns is discussed. The results indicate that upon interface rupture, Mach (head) waves, which carry a relatively large amount of energy in a concentrated form, can be generated and propagated from the interface contact region (asperity) into the acoustically softer material. Such Mach waves can cause severe damage onto a particular region inside an adjacent acoustically softer area. This type of damage concentration might be a possible reason for the generation of the “damage belt” in Kobe, Japan, on the occasion of the 1995 Hyogo-ken Nanbu (Kobe) Earthquake.

An experimental investigation of dynamic crack propagation in a brittle material reinforced with a ductile layer

The fracture behavior of a dynamically loaded edge crack in a brittle-ductile layered material, as a function of applied loading rate, was experimentally investigated. Layered specimens were prepared by sandwiching a thin layer of ductile aluminum between two thick layers of brittle Homalite-100. The layers were bonded using Loctite Depend 330 adhesive, and a naturally sharp edge crack was introduced in one of the Homalite-100 layers. These single-edge notched specimens were loaded in dynamic three-point bending using a modified Hopkinson bar. The fracture process was imaged in real time using dynamic photoelasticity in conjunction with digital high-speed photography, and the applied load and load-point displacement histories were determined from the strain signals recorded at two locations on the Hopkinson bar. The results of this study indicated two distinct mechanisms of dynamic failure, depending on the applied loading rate. At lower loading rates, the starter crack arrested on reaching the aluminum layer and then caused delamination along the aluminum–Homalite interface. On the contrary, as the loading rate was increased, interfacial delamination was followed by crack re-initiation in the Homalite layer opposite to the initial starter crack. It was determined that the times required for crack initiation, delamination and crack re-initiation decreased as the loading rate was increased. However, it was also observed that the applied load values associated with each event increased with increasing loading rate. These observations indicate that both the dynamic failure process and plausibly the failure mode transition are affected by the rate-dependent properties of Homalite, aluminum and the interfacial bond. Finally, based on the measured peak loads and the observed failure mechanisms it was concluded that the incorporation of a thin ductile reinforcement layer can increase both the overall fracture toughness and strength of a nominally brittle material.

An experimental study of impact-induced failure events in homogeneous layered materials using dynamic photoelasticity and high-speed photography

The generation and the subsequent evolution of dynamic failure events in homogeneous layered materials that occur within microseconds after impact were investigated experimentally. Tested configurations include three-layer and two-layer, bonded Homalite specimens featuring different bonding strengths. High-speed photography and dynamic photoelasticity were utilized to study the nature, sequence and interaction of failure modes. A series of complex failure modes was observed. In most cases, and at the early stages of the impact event, intra-layer failure (or bulk matrix failure) appeared in the form of cracks radiating from the impact point. These cracks were opening-dominated and their speeds were less than the crack branching speed of the Homalite. Subsequent crack branching in several forms was also observed. Mixed-mode inter-layer cracking (or interfacial debonding) was initiated when the intra-layer cracks approached the interface with a large incident angle. The dynamic interaction between inter-layer crack formation and intra-layer crack growth (or the so-called “Cook–Gordon Mechanism”) was visualized for the first time. Interfacial bonding played a significant role in impact damage spreading. Cracks arrested at weak bonds and the stress wave intensity was reduced dramatically by the use of a thin but ductile adhesive layer.

Impact failure characteristics in sandwich structures: Part I: Basic failure mode selection

In the present work we present a systematic experimental investigation of the generation and subsequent evolution of dynamic failure modes in sandwich structures subjected to low-speed impact. Model sandwich specimens involving a compliant polymer core sandwiched between two metal layers were designed and subjected to impact loading to simulate failure evolution mechanisms in real sandwich structures. High-speed photography and dynamic photoelasticity were utilized to study the nature and sequence of such failure modes. A series of complex failure modes was documented. In all cases, inter-layer (interfacial) cracks appeared first. These cracks were shear-dominated and were often intersonic even under moderate impact speeds. The transition from inter-layer crack growth to intra-layer crack formation was also observed. The shear inter-layer cracks kinked into the core layer, propagated as opening-dominated intra-layer cracks and eventually branched as they attained high enough growth speeds causing core fragmentation.

Static and dynamic fracture analysis for the interface crack of isotropic-orthotropic bimaterial

In the present study, interfacial cracks between an isotropic and orthotropic material, subjected to static far field tensile loading are analyzed using the technique of photoelasticity. The fracture parameters are extracted from the full-field isochromatic data and the same are compared with that obtained using boundary collocation method. Dynamic photoelasticity combined with high-speed digital photography is employed for capturing the isochromatics in the case of propagating interfacial cracks. The normalized stress intensity factors for static cracks are greater when α=90° (fibers perpendicular to the interface) than when α=0° (fibers parallel to the interface), and those when α=90° are similar to ones of isotropic material. The dynamic stress intensity factors for interfacial propagating cracks are greater when α=0° than α=90°. For the velocity ranges (0.1<c/c s1 <0.7) observed in this study, the complex dynamic stress intensity factor |K D |, I increases with crack speedc, however, the rate of increase of |K D | with crack speed is not as drastic as that reported for homogeneous materials.

Ultrasonic Guided Wave Inspection of Bonded Lap Joints: Noncontact Method and Photoelastic Visualization

The main topic of this paper is the nondestructive inspection of adhesively bonded lap joints by using ultrasonic guided (plate) waves. A noncontact, couplant-free method that employs capacitive air-coupled transducers is demonstrated for the inspection of thin aluminum joints with dimensions typical of aircraft fuselage and wing panels. Two types of bond defects, disbonded regions and regions of poorly cured (low-cohesive-strength) adhesive, are successfully detected by measuring the amplitude decrease of selected plate waves leaking from one adherend to the other one through the bondline. It is shown that proper choice of the vibrating mode structure, in terms of cross-sectional displacement distributions, is needed in order to maximize the sensitivity of the inspection to the presence of the low-cohesive-strength bond. Results from a dynamic photoelasticity study are also presented to visualize fundamental behavior of propagating plate waves and study their interaction with bond defects in glass lap joints. The photoelastic results confirm in a clear, pictorial manner certain assumptions on plate wave leakage through the bond, including the influence of vibrating mode structure on the detection of low-strength bonds.

Comparative study on orthotropic solid waves by time-domain BEM and dynamic photoelasticity

Experimental research and numerical analysis are two basic tools in the study of wave propagation problems in orthotropic media. In this paper, an experimental method, namely dynamic orthotropic photoelasticity, which studies the dynamic behavior of orthotropic materials on a macroscopic scale by employing orthotropic birefringent materials, is established. Meanwhile, a numerical method, namely time domain boundary element method (BEM) for wave propagation in orthotropic media, is also presented. The two methods are used together in the analysis of semi-infinite orthotropic plates with and without a circular hole modeled by a unidirectional fiber-reinforced composite under impact loading. The propagation, reflection and diffraction of stress waves in the orthotropic media are recorded experimentally and investigated. Time histories of birefringent fringe orders or stresses for specific points of the plates are obtained, respectively, from the two methods and compared with each other. The comparative study demonstrates the applicability and accuracy of the two methods for wave propagation problems in orthotropic media.

Wave propagation in fibre reinforced composite plate with circular hole under impact loading

In this paper, experimental and numerical methods have been applied to the study of composite dynamics. Dynamic orthotropic photoelasticity is employed in the experimental work and the time domain boundary element method for anisotropic media is adopted for the numerical analysis. A fibre reinforced birefringent composite plate is used to model the semi-infinite orthotropic domain with a circular hole. A rifle bullet was used to exert the impact loading with the loading direction parallel and perpendicular to the fibre direction. In the experiments, the propagation, reflection, and diffraction of the stress wave around the hole were recorded and the results were analysed. The time histories of the stress components were obtained from the same experiments and compared with the results from the corresponding computations carried out using the time domain boundary element method. Some valuable data regarding composite dynamics and associated engineering implications were obtained. The comparative study also demonstrates the applicability and accuracy of the two methods for wave propagation problems in orthotropic media.

High-speed fracture studies on bimaterial interfaces using photoelasticity—a review

Dynamic photoelasticity and high-speed photography have been combined to study fracture of bimaterial interfaces in the subsonic and intersonic regimes. The response of isochromatic fringes to various interface fracture parameters is investigated. Next, a series of experiments is conducted with specially designed specimen geometries under different loading conditions to encompass the whole range of interfacial crack propagation behaviours. The photoelastic data obtained from these experiments is carefully analysed to obtain the crack velocity, complex stress intensity factor, mode mixity and dynamic energy release rate. Finally a fracture criterion in the subsonic regime is proposed and validated with the experimental results.

Analytical and experimental study on wave propagation problems in orthotropic media

Wave propagation problems in orthotropic media are studied jointly by analytical and experimental methods in this paper. Dynamic orthotropic photoelasticity, which studies experimentally the dynamic behavior of orthotropic materials on a macroscopic scale by employing orthotropic birefringent materials, is established. A dynamic stress-optic law for orthotropic birefringent materials is postulated and practical methods of calibrating dynamic mechanical constants and dynamic stress-fringe values are proposed. Meanwhile, time domain boundary element method (BEM) for wave propagation in orthotropic media, is also presented based on the theory of elastodynamics. A scheme of stress calculations that is necessary for strength analysis is established. The paper stresses on the applications in wave propagation problems in orthotropic media by demonstrating three examples. The semi-infinite orthotropic plates with and without a circular hole modeled by a unidirectional fiberreinforced composite under impact loading are analyzed. Time histories of birefringent fringe orders or stresses for specific points of the plates are obtained respectively from the two methods and compared with each other. Based on the above comparative study, the dynamic response of an underground workshop under seismic waves is studied by time domain BEM. The responses of displacements and stresses are solved. The effects of angle and frequency of incident waves and the degree of media anisotropy on dynamic response of the underground workshop are investigated.

Experimental study on crack curving propagation in bending beams under impulsive load

Dynamic fracture behaviour of crack curving in bent beams has beeninvestigated.In order to understand the propagation mechanism of such cracks underimpact,an experimental method is used that combines dynamic photoelasticity withdynamic caustics to study the interaction of the flexural waves and the crack.Fromthe state change of the transient stresses in polymer specimen,the curving fracturein the impulsively loaded beams is analyzed.The dynamic responses of crack tips areevaluated by the stress intensity factors for the cracks running in varying curvaturepaths under bending stress wave.

Propagation behavior of the interface crack through a hole

The dynamic photoelasticity with the aid of Cranz-Shardin type high speed camera system is utilized to record the dynamically propagating behavior of an interface crack. This paper investigates determined the effects of the hole (exited on the path of the crack propagation) on the crack propagation behavior by comparing the experiment isochromatic fringes to the theoretical stress fields.

Rayleigh pulse-dynamic triggering of fault slip

AbstractWe present an experimental and numerical investigation of the interaction of a Rayleigh (R) pulse with a partially contacting strike-slip fault between similar and dissimilar materials. This study is intended to offer an improved understanding of the earthquake rupture mechanisms. The fault is subjected to static normal and shear prestresses. Utilizing two-dimensional dynamic photoelasticity in conjunction with high-speed cinematography, the evolution of time-dependent isochromatic fringe patterns (contours of maximum in-plane shear stress) associated with Rayleigh pulse-fault interaction is experimentally recorded. It is shown that fault slip (instability) can be triggered by a pulse that propagates along the fault interface at Rayleigh wave speed (about 90% of the relevant shear wave speed) and that the direction of the static shear preloading has an influence on the initiation of fault slip. For the numerical studies, a finite-difference wave propagation simulator SWIFD (solids wave impact fracture damage) is used for a quantitative analysis of the problem under different combinations of contacting materials. Dynamic rupture in laterally heterogeneous structures is discussed by considering the effect of the acoustic impedance ratio of the two contacting materials on the wave patterns. The results indicate that upon fault rupture, Mach (head) waves, which carry a relatively large amount of concentrated energy, can be generated that propagate from the fault contact region into the acoustically softer material. Such Mach waves can cause concentrated damage in a particular region located inside an adjacent acoustically softer area. This type of damage concentration might be another possible reason for the generation of the damage belt in Kobe, Japan, on the occasion of the 1995 Hyogo-ken Nanbu earthquake.

Photoelastic studies for composite dynamics

The orthotropic birefringent composites suitable for the study of dynamic photoelasticity are investigated and the determination of residual birefringence in the materials is briefly described. A stress-optic law for dynamic photoelastic analysis of orthotropic birefringent composites is postulated based on the static stress-optic law of Hyer and Liu. Subsequently, practical methods of calibrating dynamic mechanical constants and dynamic stress-fringe values are proposed. With dynamic strain measurements and time domain BEM for anisotropic media, three calibration specimens (0°, 90° and 45°) are used to verify the proposed stress-optic law in uniaxial-stress fields and a plate of unidirectional fiber-reinforced birefringent composite under impact loading, with the loading direction parallel, perpendicular and at 45° to the fiber direction, is analyzed to verify the proposed stress-optic law in biaxial-stress fields. Results show that the dynamic stress-optic law for orthotropic birefringent composites is valid in the two cases.

Dynamic Fracture Criteria for Crack Growth Along Bimaterial Interfaces

Dynamic fracture criteria based on experimental observations are proposed for subsonic crack growth along bimaterial interfaces. These criteria are based on the premise that the crack-face displacements at a point behind the crack tip increase exponentially with the instantaneous crack-tip velocity. This assumption establishes a generalized relationship between the dynamic energy release rate and the instanta-neous crack-tip velocity. Experiments are performed on PSM-1/aluminum bimaterial systems for both shear dominated and opening-mode dominated crack growth to verify the proposed criteria. Two different bimaterial specimen geometries are employed to obtain the complete range of crack-tip speeds in the subsonic regime. The dynamic loading is achieved either by detonating two explosive charges on the specimen or by impacting the specimen in one-point bend configuration. Dynamic photoelasticity in conjunction with high-speed photography is used to analyze the fracture event. Explosive loading of the interface crack results in crack propagation speeds on the order of 65 percent of the shear wave speed of PSM-1 and the crack growth is observed to be stable and opening-mode dominated. In contrast, the impact loading results in very high crack propagation speeds on the order of shear wave speed of PSM-1 and the crack growth is observed to be shear dominated.

The Effects of Motion on Dynamic Moiré Interferometry

Experimental techniques (e.g. laser interferometry, photoelasticity) that generate fringe data are currently being utilized for analyzing full-field surface deformations in a variety of dynamic problems in experimental mechanics. As opposed to static problems, the transience of surface deformations in dynamic problems poses a unique problem in accurately resolving the fringe data that is acquired. Neumann determined that for time-lapse, double-exposure holographic interferometry the fringe contrast depends on the data acquisition time, wavelength of the light source, and transience of the dynamic phenomena. Dally performed a similar analysis for dynamic photoelasticity, where the dependence was on the stress gradients instead of the wavelength of the light source. This paper attempts to extend the analysis of Neumann and Dally to the analysis of transient fringe intensity data obtained from using dynamic moiré interferometry. It is found that the fringe contrast can depend on the frequency of the fringe field rather than the wavelength of the light source or stress gradients, and the fringe contrast will decay more rapidly for Gaussian light sources than constant intensity light sources. © 1997 Elsevier Science Ltd. All rights reserved.

Subsonic and Intersonic Crack Growth Along a Bimaterial Interface

An experimental investigation has been conducted to study the dynamic failure of bimaterial interfaces. Interfacial crack growth is observed using dynamic photoelasticity and characterized in terms of crack-tip velocity, complex stress intensity factor, and energy release rate. On the basis of crack-tip velocity two growth regimes are established, viz. the subsonic and transonic regimes. In the latter regime crack-tip velocities up to 1.3 times the shear wave velocity of the more compliant material are observed. This results in the formation of a line of discontinuity in the stress field surrounding the crack tip and also the presence of a pseudo crack tip that travels with the Rayleigh wave velocity (of the more compliant material).

Using dynamic photoelasticity to evaluate the influence of parting planes on stress waves interacting with stopes: A. Daehnke, H. P. Rossmanith & R. E. Knasmillner, International Journal for Numerical & Analytical Methods in Geomechanics, 20(2), 1996, pp 101–117

Using dynamic photoelasticity to evaluate the influence of parting planes on stress waves interacting with stopes: A. Daehnke, H. P. Rossmanith & R. E. Knasmillner, International Journal for Numerical & Analytical Methods in Geomechanics, 20(2), 1996, pp 101–117