Multi-material topology optimization with strength constraints

Numerical Simulation of the Aluminum 6061-T6 Cutting and the Effect of the Constitutive Material Model and Failure Criteria on Cutting Forces’ Prediction

The mechanical response in compression of several explosives was determined as a function of temperature and strain rate. The compressive strength (maximum stress) and the Young's modulus increase with decreasing temperature and increasing strain rate and are proportional to each other. While the compressive strength and Young's modulus vary by about an order of magnitude, the strain at the maximum stress is approximately constant with variations of strain rate and temperature. This approximately constant strain, which can be used as a criteria for failure, is attributed to damage generation that is a function of strain but not temperature or strain rate.

Chapter 3.11 - A strain-energy based failure criterion for non-linear analysis of composite laminates subjected to biaxial loading

<div class="htmlview paragraph">Modeling of spot weld failure is critical in CAE analysis for vehicle crash. Force-based criterion for spot weld nugget interfacial failure is still the most familiar one and commonly used in CAE practice. However, in vehicle crash, spot weld failures often occur in the form of nugget pullout, in which the sheet metal around the nugget, rather than the nugget itself, fails and thus results in the pullout. Compared to the nugget interfacial failure, the pullout mode is more ductile and involves in the materials in and adjacent to the heat-affected-zone (HAZ) around the nugget. In this study, material failures in and adjacent to HAZ are directly modeled using strain-based failure criterion. The model consists of spot weld nugget, HAZ, and base metal (BM). The metal materials inside and outside of HAZ are treated as different materials, and the zones and subzones around the nugget may have different failure strain values. This modeling technique has been correlated with a group of test results found in the literature. The tests include two loading conditions: lap-shear and cross-tension. The tested material is high strength steel HSLA 350.</div>

Failure criteria in current engineering critical assessment procedures for defects in pipelines and welds are stress-based. For example, failure is presumed to occur when the net section average stress reaches some arbitrary flow stress. These approaches are unrealistic for defects of limited length where loading of the net section (ligament) is essentially strain controlled. In order to improve upon this, the authors developed a strain-based failure criterion for part wall pipe defects in terms of the maximum ligament plastic extension. While this criterion[l] provided a basis for assessing the criticality of blunt defects, with respect to plastic collapse, it did not address sharp or planar defects which promote fracture. As a defect becomes sharper, failure is determined more by local strain at the defect tip which is typically characterized by the crack tip opening displacement (CTOD). This paper describes the development of a sharp/planar defect strain-based failure criterion which relates the maximum ligament extension to the critical CTOD of the material. Two and three dimensional non-linear finite element analyses are used to determine local root extensions of circumferential defects which can be related to the loading, defect and pipe dimensions. The root extensions are calibrated to standard CTOD measurements through non-linear finite element analysis. The failure criterion development process considers various defect lengths, material work hardening rates and material models. The failure criterion is compared with analytical and experimental data to demonstrate its predictive capability. The end result of this work is the development of an alternative acceptance criterion for sharp weld defects permitting more effective repair decisions to be made based on a more uniform level of reliability.

Continuum damage mechanics applied to numerical analysis of ship collisions

Composite material become interest on various applications in wide industry globally. The selection of composite material due to its versatile properties for instance high specific strength. Besides, the properties of composite material also tailorable for various application including automotive, aerospace and marine industry. The objective of this study is to perform the failure analysis of composite material under transverse sinusoidal load. Both failure criteria, Maximum Stress and Tsai-Wu Failure Criteria that provided in ANSYS used to carry out the analysis. Various aspect ratios will be used which are 5, 10, 20, 50 and 100 to perform the analysis with different thickness of laminate. Next, the boundary condition of the plate was set to simply and clamp supported. The finite element analysis of graphite/epoxy laminate with layup of (0/90/90/0) performed to determine the failure loads (First Ply Failure, FPF and Last Ply Failure, LPF loads). The un-normalized load obtained from the analysis is converted to normalized load using equation given. Finally, normalized load is plotted against aspect ratio for both failure criteria and boundary conditions.

The progressive failure analysis of composite bolted joints under thermal environment has been investigated using the finite element method. The emphasis has been on the computational aspects of the problem. The ultimate failure loads and pin-bearing stresses have been computed using different failure criteria and the results have been compared with the experimental data as published in the open literature. In reality, bolted joints have been employed to various situations where the amount of load to be transferred is relatively high and on many occasions thermal effect is an important consideration. So the effect of material property degradation due to temperature has also been considered in this investigation. Progressive damage analyses have been performed for different laminates to give complete load-deflection path beyond failure load that will serve as a future reference. The pin has been modeled as a rigid object and load has been imparted on the structure as a displacement-controlled process to simulate the experimental situation in the laboratory environment. Contact between the bolt and the laminate has been considered in the analysis. A number of “User Subroutines” for ABAQUS software have been developed to incorporate Hashin, maximum stress, and Tsai-Wu failure criteria in the analysis. The effectiveness and performance of various well-known failure criteria as mentioned above have been evaluated and the results have been presented in graphical form.

Peel data for two epoxy adhesives and a recent model of the adhesive stresses in the peel geometry are used to investigate the effectiveness of two constitutive models and several adhesive failure criteria. The failure criteria are based on either the critical strain energy-release rate or the critical von Mises strain at the peel root, both taken as functions of the “loading zone length” (LZL), defined as a measure of the degree of stress concentration at the root of the peeling adherend. The peel model uses LZL as an independent parameter that captures the effects of the peel angle, adherend thickness, and the mechanical properties of the adhesive and adherend. Both the energy- and strain-based failure criteria can be used to predict the steady-state peel load with an average absolute error of less than 10% over the range of conditions that were examined.

Coal-based carbon foam (CCF) has broad application prospects in aerospace, composite material tooling and other fields. However, the lack of failure criteria limits its promotion. In previous studies, the failure criteria of similar materials were proposed, but there are some limitations. This paper proposes improved failure criteria based on macro-mechanical tests. Furthermore, uniaxial and multiaxial loading tests were carried out to obtain accurate failure criteria of CCF. Finally, 3-points bending tests of the CCF sandwich structure were conducted and their finite element models (FEMs) were established. The CCF test results show that the mechanical properties of CCF are transversely isotropic. The failure criteria in this paper can accurately predict the stress when the CCF fails. The error band boundary formula caused by the dispersion of the material were also given. The maximum load Pmax calculated by the failure surface (3684 N) was only 4.7% larger than the mean value measured by the test (3518 N), and all of the Pmax measured by the test (3933 N, 3640 N, 3657 N, 3269 N, 3091 N) were between the maximum value (4297 N) and minimum value (3085 N) calculated by the error band boundary formula, which means that the failure criteria have good precision.

Three-dimensional invariant-based failure criteria for fibre-reinforced composites

Implementation of failure criteria for transverse failure of orthotropic Non-Crimp Fabric composite materials

The bond strength of adhesively bonded timber–concrete composites (ATCC) with prefabricated concrete elements is usually described using the shear strength of the timber. This approach, however, often fails to consider the actual failure modes of the bondline and also the interaction between shear stresses and stresses perpendicular to the bondline has not yet been comprehensively understood. To address this limitation, a reliable calculation method is required, where stress determination, failure criterion, and stress analysis are clearly defined to accurately predict the bond failure of ATCC specimens. In this study, three linear-elastic calculation methods and one non-linear calculation method are presented along with corresponding failure criteria and strength parameters. Regarding validation, the predicted failure load is compared to experimental results from 186 ATCC bond specimens to assess the method’s suitability. Based on the findings, appropriate calculation methods for a reliable prediction of the bond strength are recommended.

The relationship between energy-based (interfacial toughness, Gic) and stress-based (ultimate shear strength, τult) criteria of interfacial failure in micromechanical tests is investigated within the frames of the Nairn shear-lag approach. To determine which criterion is responsible for interfacial failure in particular fiber-polymer systems, the data obtained in microbond tests for the joints of carbon, glass and aramid fibers with various thermoplastic and thermosetting matrices are analyzed. Experimental relations between the debond force and the embedded fiber length appear to be satisfactorily described by curves plotted according to both theories. It is demonstrated that, in a similar way as a deformed spring can be equally characterized by the reaction force and potential energy, both ultimate shear strength and energy release rate (as well as any combination of those) can be measures of interfacial strength. However, only such function f = f(Gic, τult) can be a real characteristic of the bimaterial interface (rather than of the particular specimen only), which does not depend on the specimen geometry. Theoretical consideration of micromechanical tests has shown that of all geometrical dimensions of a specimen, the fiber diameter, d, has the most prominent effect on the calculated value of the failure criterion. The analysis of data available in literature on microbond experiments with glass fibers having different diameters has revealed that for the glass fiber/epoxy matrix τult is proportional to d-½ and Gic is approximately constant; consequently, interfacial failure can be considered as energy-controlled.

Short-term behavior of glass fiber-polymer composite bending-active elastica beam under service load application