Photoelasticity

About: Photoelasticity is a research topic. Over the lifetime, 2698 publications have been published within this topic receiving 27957 citations.

Polarization-sensitive optical coherence tomography for photoelasticity testing of glass/epoxy composites.

Abstract: We measure the spatial distribution of the mechanical stress induced inside translucent glass/epoxy composites by means of polarization-sensitive optical coherence tomography. The Stokes parameters determined from two orthogonal polarization components of the backscattered light allow the internal stress to be identified in terms of its magnitude and principal direction based on a birefringence light scattering model of glass/epoxy composites. Measurement examples show the particular case of stress concentration near a through hole and the internal structural damages caused by excessive tensile loading.

Dynamic crack deflection and penetration at interfaces in homogeneous materials: experimental studies and model predictions

Abstract: We examine the deflection/penetration behavior of dynamic mode-I cracks propagating at various speeds towards inclined weak planes/interfaces of various strengths in otherwise homogeneous isotropic plates. A dynamic wedge-loading mechanism is used to control the incoming crack speeds, and high-speed photography and dynamic photoelasticity are used to observe, in real-time, the failure mode transition mechanism at the interfaces. Simple dynamic fracture mechanics concepts used in conjunction with a postulated energy criterion are applied to examine the crack deflection/penetration behavior and, for the case of interfacial deflection, to predict the crack tip speed of the deflected crack. It is found that if the interfacial angle and strength are such as to trap an incident dynamic mode-I crack within the interface, a failure mode transition occurs. This transition is characterized by a distinct, observable and predicted speed jump as well as a dramatic crack speed increase as the crack transitions from a purely mode-I crack to an unstable mixed-mode interfacial crack.

Digital photoelasticity: Principles, practice and potential

Abstract: The enormously enhanced power of photoelasticity resulting from adoption of digital technologies is highlighted and discussed. An overview of the principal techniques of digital fringe processing is provided within a single theoretical framework. The practical application of the new technologies using both conventional instruments and novel optical devices is discussed. Experiments involving more I x 10 6 quantitative fringe order measurements are possible and practical on a routine basis using the current technology. Products based on this research are beginning to appear on the market so that many new application areas are opening up for photoelasticity, such as dynamic events, real-time fatigue crack analysis, monitoring polarisation changes at a microscopic level in materials; detailed validation of numerical simulations, particularly of complex geometry and loading; and in-service monitoring using reflection photoelasticity of damage in both homogeneous and heterogeneous materials, such as composites.

Dynamic fracture of a functionally gradient material having discrete property variation

Abstract: A functionally gradient material (FGM) with discrete property variation is prepared, and the dynamic fracture in this material is studied using the technique of photoelasticity combined with high-speed photography Transparent sheets required for the study are made by casting a polyester resin mixed with varying amounts of plasticizer The mechanical (quasi-static and dynamic) and optical properties of the material are evaluated as a function of the plasticizer content Results of material characterization show that the fracture toughness increases with increasing plasticizer content, whereas the Young's modulus decreases The material fringe constant and the dynamic modulus are observed to be relatively insensitive to plasticizer content The FGM is then prepared by casting together thin strips having different plasticizer content The dynamic crack propagation phenomenon is studied for four different property variations along the crack propagation direction, and the effects of these property variations on crack speed, crack jump distance and dynamic stress intensity factor are investigated Results of this investigation show that increasing the toughness in the direction of crack growth reduces the crack jump distance as compared to on increasing-decreasing toughness variation for the same initial energy

Towards a new model of crack tip stress fields

Abstract: This work introduces a novel mathematical model of the stresses around the tip of a fatigue crack, which considers the effects of plasticity through an analysis of their shielding effects on the applied elastic field. The ability of the model to characterize plasticity-induced effects of cyclic loading on the elastic stress fields is assessed and demonstrated using full-field photoelasticity. The focus is on determining the form of the shielding stress components (induced by compatibility requirements at the elastic–plastic interface along the crack flank and via the crack tip plastic zone) and how they influence the crack tip elastic stress fields during a load cycle. The model is successfully applied to the analysis of a fatigue crack growing in a polycarbonate CT specimen.