Effect of open joint on stress wave propagation

Stress wave characteristics are drastically altered by joints and other inhomogenities. This paper addresses the effect of an open joint on stress wave transmission. An elastodynamic analysis is developed to supplement and explain some recent observations by Fourney and Dick(1995) on open as well as filled joints. The analytical model developed here assuming spherical symmetry can be extended to filled joints between dissimilar media, but results are presented only for open joints separating identical materials. As a special case, stress wave transmission across a joint with no gap is also addressed

Interactions of interfacial arc cracks

The interaction of two interfacial arc cracks around a circular elastic inclusion embedded in an elastic matrix is examined. New results for stress intensity factors for a pair of interacting cracks are derived for a concentrated force acting in the matrix. For verifying the point load solutions, stress intensity factors under uniform loading are obtained by superposing point force results. For achieving this objective, a general method for generating desired stress fields inside a test region using point loads is described. The energetics of two interacting interfacial arc cracks is discussed in order to shed more light on the debonding of hard or soft inclusions from the matrix. The analysis based on complex variables is developed in a general way to handle the interactions of multiple interfacial arc cracks/straight cracks

Invariant points on energy contours around a crack tip under mixed mode loading

The locus of points around a crack tip where the strain energy density is set equal to a critical value reveals interesting features. It is seen that, for certain cases, two points on this locus remain invariant with respect to the phase of the applied loads. The existence of these invariant points is examined for different configurations - a crack in a homogeneous isotropic medium, an interface crack and an inclined interface crack. This analysis is extended to the two components of strain energy density – volumetric (VSED) and distortional (DSED)

Tomographic data acquisition in axisymmetric specimens

Fringe patterns for axial, radial and angular incidences can be analyzed later for extracting the photoelastic unknowns and hence individual stress components. Axisymmetric specimens can thus be analyzed nondestructively in a whole-field manner. The quality of optical data acquisition with this system is consistently high due to high levels of scattered light intensity. This method is particularly attractive because even a low power laser is sufficient for data acquisition. Though we have demonstrated fringes using a stress-locked specimen, live loaded specimens can also be examined provided suitable loading fixtures are built to generate high stresses in three dimensional models. High stress levels are necessary to induce sufficient fringes for recording

Characterizing Frictional Contact Loading via Isochromatics

Isochromatic patterns in the vicinity of frictional contacts furnish vital clues for characterizing friction. Though friction effects are evident in a diametrally loaded circular disk, three-point loading provides better results towards highlighting friction. In this paper, a new method of characterizing friction at loading contacts using photoelastic isochromatics patterns is presented. Location of isotropic points (IPs) formed in three-point and four-point loadings of circular disk is used as a main tool to quantify the friction component using theoretical analysis. Bifurcation of isochromatic fringe loops near the distributed loads is explained by the presence of anti-symmetric Hertzian shear traction in addition to Hertzian normal traction. The classical solution by Flamant for point load at the edge of half plane is used to derive stresses in circular disk for all required loading configurations. A semicircualr ring under three-point loading is examined using photoelasticity to understand the isochromatics pattern theoretically by considering normal and shear traction components at loaded regions

Mixed Mode Analysis of Obliquely Oriented Edge Cracked Semicircular Disk Under Compression

A new mixed-mode compression fracture specimen, obliquely oriented edge cracked semicircular disk (OECSD) is analyzed by extending pure opening mode configuration of edge cracked semicircular disk (ECSD) under Hertzian compression. Photoelastic experiments are conducted on two different specimens of OECSD of same size and different crack lengths and inclinations. Finite element method (FEM) is used to solve a number of cases of the problem varying crack length and crack inclination. FE results show a good match with experiments. Inclination of edge crack in OECSD can be so made as to obtain any mode-mixity ratio between zero and one and beyond for any crack length. The new specimen can be used for fracture testing under compression more conveniently than the existing ones in several ways

Design and analysis of novel compression fracture specimen with constant form factor: Edge cracked semicircular disk (ECSD)

Inspired by the Brazilian disk geometry we examine the utility of an edge cracked semicircular disk (ECSD) specimen for rapid assessment of fracture toughness of brittle materials using compressive loading. It is desirable to optimize the geometry towards a constant form factor F for evaluating K-I. In this investigation photoelastic and finite element results for K-I evaluation highlight the effect of loading modeled using a Hertzian. A Hertzian loading subtending 4 degrees at the center leads to a surprisingly constant form factor of 1.36. This special case is further analyzed by applying uniform pressure over a chord for facilitating testing

Interface crack around circular inclusion: SIF, kinking, debonding energetics

The problem of an interfacial arc crack around a circular elastic inclusion embedded in an elastic matrix is examined. A general approach for generating uniform/non-uniform stress fields inside a test region through remotely applied point loads is demonstrated. The effects of stress gradient, arc crack angle, and elastic mismatch are discussed. Interfacial arc crack kinking is examined using the maximum tensile stress criterion only for such cases wherein the crack is open. Finally, the energetics of inclusion debonding is addressed for the specific case of hydrostatic loading

Analytical and Experimental Evaluation of Coldworking Process for Strain Hardening Materials

A detailed analysis of coldworking to evaluate the extent and movement of elasto-plastic front, considering both elastic strains and strain hardening effects, is developed. The elasto-plastic solution for a plate specimen with a hole subjected to internal pressure is developed using modified Nadai's auxiliary variable and von Mises yield criterion. A parametric study is carried out to investigate the effect of specimen width on pressure requirement for a given extent of elasto-plastic boundary. It is observed that for a specified elasto-plastic boundary the displacement at the edge of the hole varies linearly with the pressure. It is also observed that with increase in strain hardening, the pressure required is higher and the corresponding displacement at the edge of the hole is smaller in magnitude. Residual stresses decrease with increase in strain hardening. The method evolved here correlates the necessary pressure with the radial expansion using a mandrel to achieve the same amount of coldworking