Proper Failure Criterion Research Articles

Failure surfaces of high-strength materials predicted by a universal failure criterion

Advanced high-strength materials including metallic glasses (MGs) and nanocrystalline (NC) metals have attracted great attentions due to their promising mechanical properties. However, since they usually exhibit relatively brittle fracture behavior, a proper failure criterion is urgently required for the safety design of structural components and devices using these high-strength materials. It has been found that the conventional failure criteria may not soundly explain the fracture behaviors of MGs, while the ellipse criterion shows promising universality for well describing the fracture behaviors of several kinds of high-strength materials under various loading conditions. In this study, the principal stress form of the ellipse criterion was derived for the first time, and the two-dimensional failure surfaces according to this criterion were plotted and compared with the other predictions, as well as the experimental and simulation results of MGs and NC metals. The results confirm the applicability of the ellipse criterion for predicting the failure of high-strength materials, and may also improve the understanding of strength and fracture of various materials.

A modified method for predicting the stresses around producing boreholes in an isotropic in-situ stress field

Rock formations are always under in situ stresses due to overburden or tectonic stresses. Drilling a well will lead to stress redistribution around the well. Understanding such a stress redistribution, and adopting a proper failure criterion, play a vital role in predicting any potential wellbore failure. However, most of the published analytical models are based on assumptions that do not satisfy the boundary conditions during production, that is, when the well pressure is less than the pore pressure. This paper is aimed at the modeling of the stress regime around the wellbore through combining the poroelastic model with proper boundary conditions under different flow regimes. As a result, a new model is presented to calculate the stresses around the well under Darcy and non-Darcy flow conditions. Covering the non-Darcy regime makes the new model applicable to gas reservoirs with non-Darcy flow. The results of this new model have been compared with the results of other models previously published in the literature. The results show that the new model convergence at the boundary condition is superior to other models used in the oil and gas industry.

Comparative Analysis of Crack Resistance of Fiber-Metal Laminates with HS2 Glass/T700 Carbon Layers for Various Stress Ratios

Fiber-metal laminates (FMLs) composed of metal lamina and reinforcing fibers exhibit an improved crack growth resistance as compared to conventional aircraft materials. The crack resistance of a hybrid FML composite consisting of LY12M aluminum alloy lamina and prepreg layers of HS2 glass fibers and T700 carbon fibers has been experimentally investigated on tensile specimens at stress ratios R = - 1, 0.1, and 0.5. The crack growth rate data at positive stress ratios demonstrate a significant scatter and a large difference between specimen's back and front surfaces formed by 1-mm thick outer aluminum layers. This violation of the test standard requirements for metal materials in the performed FML tests presents a problem of determining a proper failure criterion for the engineering applications of FMLs. Based on the comparative analysis of FML crack resistance results obtained, some qualitative conclusions are drawn on solving this problem.

Numerical estimation and practical validation of Hooputra’s ductile damage parameters

Forming limit diagram (FLD) is a useful criterion for damage prediction, but not suitable for complex operations. Hooputra’s ductile damage (HDD) is a proper failure criterion which relies on three relatively difficult experimental tests for each material. In this paper, first, using the FLD criterion, the required difficult experimental tests of HDD criterion are simulated and the HDD parameters for St14 steel are numerically estimated. Then, to evaluate the obtained HDD parameters, damage behavior of the material in a number of benchmark tests is numerically predicted, employing the HDD criterion. Finally, the simulated results are compared with the practical observations and the identified HDD parameters are validated. Comparison of the results reveals the HDD parameters can be numerically and properly extracted, utilizing the FLD and avoiding the difficult experimental tests.

Development of a failure criterion for asphalt mixtures under fatigue loading

The failure criterion defines the applicable region associated with the continuum damage model and is important in characterising the service life of asphalt mixtures. A proper failure criterion should consistently predict the failure of the material that reaches macro-fracture. A previously developed criterion that uses the viscoelastic continuum damage (VECD) model exhibits high variability and is considered to be inefficient because it requires calibration tests at different temperatures. In this paper, a new concept that involves released pseudo strain energy is introduced. This released pseudo strain energy concept focuses on the dissipated energy that is related to stiffness reduction only and is fully compatible and predictable using the VECD model. A characteristic relationship is found between the stable rate of pseudo energy release during testing and the final fatigue life of the same mixture, independent of strain amplitude and temperature. Based on these observations, a new failure criterion is proposed. The proposed failure criterion combines the advantages of the VECD model and this characteristic relationship, which both originate from fundamental mixture properties, and is able to predict the fatigue life of asphalt concrete mixtures across different temperatures and strain amplitudes.

Evaluation on Failure of Fiber-Reinforced Sand

Fiber reinforcement can help to enhance soil strength, stabilize near-surface soil layers, and mitigate the risk of soil liquefaction. Evaluation of the strength of fiber-reinforced soils needs a proper failure criterion. This study presents a three-dimensional failure criterion for fiber-reinforced sand. By assuming that the total strength of the composite is a combination of the shear resistance of the host soil and the reinforcement of fibers, a general anisotropic failure criterion is proposed with special emphasis on the effect of isotropically/anisotropically distributed fibers. An anisotropic variable, defined by the joint invariant of the deviatoric stress tensor and a deviatoric fiber distribution tensor, isintroducedinthecriteriontoquantifythe fiberorientationwithrespecttothestrainrate/stressdirectionatfailure.Withfurtherconsideration of the fiber concentration and other factors such as aspect ratio, the proposed criterion is applied to predicting the failure of fiber-reinforced sand in conventional triaxial compression/extension tests for both isotropically and anisotropically distributed fiber cases. The predictions are in good agreement with the test results available in the literature. The practical significance of using this criterion for such problems as inclinedslopestabilizationisbrieflydiscussed.DOI:10.1061/(ASCE)GT.1943-5606.0000737. © 2013 American Society of Civil Engineers. CE Database subject headings: Fiber reinforced materials; Failures; Anisotropy; Triaxial tests; Slope stability; Sand (soil type). Author keywords: Fiber-reinforced soil; Failure criterion; Anisotropy; Fiber distribution tensor; True triaxial tests; Slope stabilization.

ESD robust high-voltage active clamps

Using circuit simulation extended by a proper failure criterion, the HBM and TLP robustness of high-voltage clamps can be accurately predicted without the need for test silicon. Electrical measurements, physical damage analysis, and device simulation have proved that the drain junction breakdown voltage constitutes the proper failure criterion for our HV active clamps.

A study on low-velocity impact damage of Z-pin reinforced laminates

Based on a low-velocity impact test, four main modes of low-velocity impact damage, including matrix cracking, delaminating, fiber failure and matrix crushing, are taken into account. By using the proper failure criterion, the lowvelocity impact damage of z-pin reinforced laminates can be realized. The results of FEM simulation, which indicate that a z-pin makes the area of delamination reduced by approximately 50%, are in good agreement with the experimental C-scan results.

Hypervelocity penetration of tungsten alloy rods into ceramic tiles: experiments and 2-D simulations

A series of terminal ballistics experiments and 2-D simulations, with small scale tungsten alloy penetrators, was performed in order to quantify the ballistic efficiency of confined ceramic tiles. The data includes both depth of penetration (DOP), into thick steel backing and X-ray shadowgraphs during the penetration process. Impact velocities ranged between 1.25 to 3.0 km/s. The size of the tiles varied in order to check their performance as a function of thickness and lateral dimensions. We found that the differential ballistic efficiency of alumina tiles is practically independent on impact velocity and tile thickness, within the ranges of velocity and thicknesses, investigated here. A detailed simulation study, using the Eulerian processor of the PISCES 2-D ELK code, was performed in order to better understand the interaction between long-rods and ceramic tiles, and particularly, to adjust a proper failure criterion to the tiles. We found that a simple version of the Johnson-Holmquist model, with a single parameter, is fairly adequate to account for most of the data. These include: lateral confinement, tile thickness and impact velocity influence on the penetration depth. We used the code to further investigate the influence of lateral dimensions on tile performance.