The Journal of Strain Analysis for Engineering Design

This paper presents a failure model to simulate the crushing mechanisms of fabric composite materials. In order to realize delamination processes and resulting lamina bending modes a multi-layered discretization is applied which is composed of shell and solid elements representing the laminate plies and the resin phase. The differentiation between the two phases enables the implementation of both in-plane failure and delamination fracture criteria and appropriate parametric degradation functions. To verify the fracture and degradation model, quasi-static tests with various compression directions have been carried out. The tests were performed using truncated conical shells of different specimen geometries fabricated with glass/epoxy prepreg. Among a qualitative comparison of the experimental and simulated failure behaviour the numerical model parameters are mainly obtained by curve fitting based on the measured load characteristics. The numerical simulations compare well with the experimental results, proving the applicability of the model for fabric composites under various loading conditions.

This paper presents an experimental remeshing process for the large strain analysis of fine-blanking. The research is to be carried out mainly because the severe and localized deformation of fine-blanking greatly obstructs the measurement of strains. In order to solve this problem, a new experimental remeshing process was developed to measure the strain in the major deformation areas of fine-blanking. Without this newly developed process, a more intensive and practical strain analysis of fine-blanking could not have been achieved. Therefore, a study of this remeshing process, with a step increment of 20 per cent, until the total punch penetration is 80 per cent of the material's thickness, is to be performed to verify its effectiveness. Low-carbon steel sheets of JISG3101 were used to split blanks. As a consequence, findings showed that an increase in the total punch penetration will clearly induce an exponential increase in the effective strain, and the severity of deformation will be augmented with the increase in the total punch penetration.

The stress analysis of a rotating finite cross-ply laminated composite hollow cylinder with two ends simply supported is conducted with the Coriolis acceleration effect involved. The state-space approach is employed together with the layerwise method as well as the Fourier expansion technique. The analysis is completely based on the exact elasticity equations so that hollow cylinders with arbitrary thickness can be readily dealt with. Numerical comparison with exact solution of a rotating infinite hollow cylinder without the Coriolis effect shows good agreement.

To evaluate the strains in a steel bar of a reinforced concrete structure under repeated loads, a mechanical model is proposed. More precisely, a reinforcing bar embedded in a concrete cylinder subjected to uniaxial actions is modelled. In the proposed one-dimensional approach, both the nonlinear fracture mechanics of concrete and the bond-slip between the two materials are taken into account, since they affect the structural response of several reinforced concrete structures in the serviceability conditions and in the ultimate limit state. When cyclic actions are applied and previous cracks close up again, the interaction between the fictitious crack model of concrete in tension and the bond-slip near the crack is investigated. During the unloading phase of each cycle, only through refinement of the damage effects, with regard to the classical bond and cohesive models, can the hysteretic behaviour of the reinforced concrete structures be modelled. The strains in the bar, computed with the proposed model, seem to be in good agreement with those measured in the tests made by Bresler and Bertero.

In this work, the capability of the synchrotron X-ray diffraction technique to measure changes in the residual strains caused by fatigue crack growth from cold-expanded holes in an aluminium alloy plate has been investigated. The measurement technique was validated by comparing the synchrotron measurements around uncracked holes with those obtained on similar specimens using the neutron diffraction and Sachs' techniques. Measurements were performed with and without superimposed tensile mechanical loading and the results compared with analytical results. The improved spatial resolution of the synchrotron technique relative to the other methods has allowed the strain fields around a fatigue crack growing from a cold-expanded hole to be evaluated in the unloaded state and at two loading levels. Only at the higher load does the crack appear to open along its full length.

Elastic stress concentration factors (SCFs) for internally pressurized thick cylindrical vessels with radial and offset circular and elliptical crossholes are presented. Three forms of intersection between the crosshole and main bore are considered: plain, chamfered and blend radiused. The minimum SCF was found to occur for the plain intersection configuration, with the peak stress at the crotch corner between the main bore and crosshole on the longitudinal plane of symmetry. Incorporating a chamfer or blend radius at the intersection reduces the stress concentration at the main bore but introduces higher peak stress elsewhere in the chamfer or blend region.

This paper presents measurements performed using an integrated centre hole drilling-deep hole drilling technique on two components: a butt-welded plate and a rail. The results were compared with those available from other measurement techniques and with finite element (FE) simulations of the residual stresses. It was found that incremental centre hole drilling and deep hole drilling worked well as complementary techniques. Subsurface deep hole drilling measurements performed in the welded plate at two locations produced very similar results and evidence of good repeatability. The present experimental results were found to be in reasonable agreement with other measurements and FE predictions of residual stresses.

A general finite element procedure with an eight-noded isoparametric curved quadratic element is presented to investigate the static behaviour of laminated composite hyperbolic paraboloidal shells bounded by straight edges (commonly called hypar shells). Numerical results are obtained for uniformly loaded laminated composite hypar shells with six practical boundary conditions, where the edges are differently restrained. Eight different types of lamination including single layered and multi-layered, cross-ply and angle-ply, symmetric and antisymmetric stacking orders are chosen. The numerical results of different shell actions of 48 combinations are furnished to estimate their relative performances. The authors further propose typical comparative performance matrix to study the relative efficiencies of different stacking combinations, which will be a great help in design.

This paper describes general techniques for predicting notch stresses and strains under elastic-plastic and creep conditions. A linear interpolation method, usually used in creep analysis, is adapted for use in predicting elastic-plastic stresses and strains and the Neuber and the Molski-Glinka methods, usually used in elastic-plastic analyses, are adapted to predict peak creep stresses at notches in components. The accuracy of the methods is assessed by comparing predictions based on them with results obtained from elastic-plastic and creep finite element analyses.

This work seeks to investigate the static and fatigue properties and the failure mechanisms of T300/QY8911 carbon-fibre-reinforced composite laminates with different layups to optimize the stacking sequence effect. Three different layups have been studied, namely, [45/0₂/-45/90₂/-45/0/45/90]_s, [45/-45/0/-45/0/45/90/45/0/-45]_s and [45/0/-45/0/-45/0/45/0/90/0]s. The results for static strength and fatigue residual strength under different fatigue stress amplitudes are evaluated and compared with each other. The damage and failure mechanisms of the composite laminates are discussed. It is observed that all tension-tension fatigue damage patterns of the notched laminates are similar while the tension-tension fatigue properties vary with the laminate layup. The reduction of stress concentration caused by the tension-tension fatigue damage leads to an improvement of the residual strength of the notched specimens in contrast to their static strength properties. The damage mechanics of the notched laminates under compression-compression loading are more complex than those of the tension-tension fatigue specimens; their damage patterns are influenced by the test clamping fixture, the layup, the size of specimens and the diameter of the hole. The residual strengths are lower than those of the specimens without fatigue damage. It is verified that in a high-temperature and moisture environment, there is a decrease in static compression strength. The results of this study provide an insight into fatigue damage development in composites and constitute a fundamental basis for the development of a strain-based residual strength model.

This paper outlines a practical model to evaluate fatigue residual strength for reliability-based design. A new formulation is presented for a fatigue-driven residual strength surface based on controlling fatigue strain. The parameter determination formulae of the residual strength surface are established to deal with the test data effectively and easily. Finally, the model is applied to experimental data, demonstrating the practical and effective use of the proposed model. It is shown that fatigue-driven residual strength can be obtained realistically according to the small sample test data using the new formulae.

The Williams' solution for the state of stress near the apex of an elastic wedge is used to study the traction distribution adjacent to the tip of a complete contact. Assuming that the surfaces remain in contact during loading, the coefficient of friction needed to ensure local adhesion is found. This is compared with that predicted by an analysis of an elastic rectangle clamped between elastic halfplanes and is shown to be consistent. The results are appropriate to all complete contacts between elastically similar components.