Material Failure Criteria Research Articles

Experimental and numerical investigation on the response of stiffened panels subjected to lateral impact considering material failure criteria

A series of experiments have been conducted to investigate the dynamic response of stiffened panels. The uniaxial tension experiments and the dynamic experiments were conducted to obtain the material characterization. The falling weight experiments were conducted to study the dynamic response of the stiffened panels. A dynamic BWH criterion which combines the BWH criterion and the Cowper-Symonds model is proposed to evaluate the material failure. The scaled constant strain (CS) criterion can decrease the influence of mesh size and improve the accuracy of the simulations. These two different criteria are applied in the simulation models and the simulation results are compared with the experiments. The simulations of the experiments are carried out using the explicit solver of the finite element software package Abaqus. The dynamic BWH criterion is implemented in the numerical simulation using user material subroutine (VUMAT). The simulation results show that the dynamic BWH criterion is better consistent with the experimental results than the scaled CS criterion. Because the influence of stress state and strain rate on material failure has been considered in the dynamic BWH criterion. The formation mechanism of different fracture shapes of the stiffened panels is discussed.

THE USE OF NONLOCAL CRITERIA IN FORECASTING FRACTURE OF QUASI-BRITTLE MATERIAL WITH A HOLE UNDER COMPRESSION

The study is aimed at the development of the new failure criteria for quasi-brittle materials in conditions of stress concentration. The possibility of using non-local failure criteria for description of the brittle, quasi-brittle and ductile fracture of the materials with notches is analyzed. The general feature of these criteria consists in the introduction of the internal dimension characterizing the structure of the material, which provides the possibility of describing a large-scale effect in conditions of the stress concentration and thereby expand the area of their application compared to traditional criteria though it is limited to the cases of brittle or quasi-brittle fracture with a small pre-ffacture zone. To broaden the scope of their application to quasi-brittle fracture with a developed pre-fracture zone we propose to abandon the hypothesis about the size of the pre-fracture zone as a constant related only to the structure of the material. A number of the new nonlocal criteria, which are the development of the criteria of the mean stress and fictitious crack, are developed, substantiated from the physical standpoint, and proved experimentally. These criteria contain a complex parameter characterizing the size of the pre-fracture zone and taking into account not only the structure, but also the ductile properties of the material, specimen geometry and loading conditions. The expressions for the critical pressure in the problem of tensile crack formation upon compression of the samples of geomaterials with a circular hole are derived. The results of calculations match rather well the experimental data on the destruction of drilled gypsum slabs.

Development of a new physical modeling method to investigate the effect of porosity on the parameters of intact rock failure criteria

Porosity is a critical textural parameter in the complex nature of rock and while it has the highest impact on the strength of intact rock, in the case of oil and gas reservoir rocks, it defines the capacity and permeability of the reservoir. A constant value for triaxial strength factor (mi) of rock failure criterion has been given for each type of sedimentary rocks such as sandstone and the effect of porosity on the mi has not been well defined. Rock is not a homogenous material as with varying the porosity, the other inherent variables also control the strength and the mechanical behavior. Rock porosity varies in a wide range in sedimentary rocks such as sandstone. In this study, the effect of porosity on the parameters of failure criteria (mi) for rock-like materials made from cemented grains is investigated. For sample preparation, a mixture of cement-sand-water was compacted with variable water content to obtain specimens having a wide range of porosities using the same grain size of filler material. Two types of grains including sand and silica filler material were used for the experimental program. Sixteen sets of artificial specimens having porosities from 9.00% to 34.09% have been prepared for two filler materials of sand and silica, while other factors affecting the strength have been kept constant. The triaxial strength test results of these specimens show that the triaxial strength factor (mi) of Hoek et al. failure criterion, internal friction angle (ϕ), and cohesive strength (C) significantly decrease with increasing the porosity. The best-fit curves follow power function with high coefficients of regression.

Multi-parameters mechanical modeling to derive a confinement model for masonry columns

Abstract Increments of the axial capacity of existing masonry elements can be provided by confinement. Assessment methodologies with general validity to assess the behavior of confined masonry columns with strengthening systems are not available in the technical literature, in fact, the strong variability and heterogeneity of masonry material did not allow to develop generalized models. For brittle materials damage mechanics and failure criteria allow to do this in the framework of solid mechanics. However, the recent scientific researches provided relevant information about the experimental behavior of masonry confined with composites. In this paper, an analytical model able to assess the behavior of the confined masonry with composite is proposed. It was developed according to a failure criterion based on mechanical parameters representative of masonry. It can be applied to masonry cross sections of any shape also under a non-uniform lateral stress field (i.e. generic stress fields). To confirm the flexibility of the proposed model some existing experimental results have been used. The comparison between model predictions and experimental results in terms of axial strength showed that the proposed model is a valid tool to assess the confinement properties of strengthened masonry elements.

Study on the Effect of Temperature on Dynamic Characteristics of Rotor System with Straight Crack

The effect of temperature on the dynamic characteristics of cracked rotor is studied in this paper. The crack is simulated by the extended finite element method (XFEM). Based on the theory of fracture mechanics, appropriate fracture criteria are selected, and the damage and failure criteria of materials are set up, and the finite element simulation analysis is carried out. The results show that with the increase of temperature, the amplitude of 3X in frequency domain increases most obviously, and the deformation degree of axis trajectory is high. The research results have important reference value and scientific significance for the study of dynamic characteristics of cracked rotor system under high temperature environment.

Biaxial constitutive relationship and strength criterion of composite fabric for airship structures

Given their irreplaceable advantages such as high strength-to-weight ratio, composite fabrics have been widely applied and studied. However, due to the limitation of specimen design and test procedure, integral biaxial constitutive relationships and valid failure criteria of composite fabrics were unavailable while desirable. In this study, typical composite fabrics for airship structures were employed to manufacture self-designed double-layer cruciform specimens as biaxial tensile tests were performed subsequently. Since the stiffness of the specimen was reasonably distributed, biaxial tensile failure characterizing the biaxial tensile strength under various warp-to-weft stress ratios was acquired. Two failure modes, the cross slits rupture and the single slit breakage, occurred when specimens reached load-bearing capacities. Furthermore, the digital image correlation approach was utilized to record the strain field during the whole test process. According to the test data, integral stress-strain curves and analytical biaxial stress-strain response surfaces were calibrated, developed and interpreted thoroughly. Since significant deviation was observed in previous failure criteria for rigid composite materials, a novel biaxial failure criterion was firstly proposed which could perfectly comply with the failure envelope obtained from the test results. As the accuracy of the failure criterion was verified, physical, mechanical and mathematical explanations for the novel failure criterion were finally illustrated.

Probabilistic failure analysis of reinforced concrete beam-column sub-assemblage under column removal scenario

Column removal failure is a common failure type of reinforced concrete (RC) structures subjected to progressive collapse. Thus, it is widely adopted to use the experimental/numerical column removal scenario to assess the progressive collapse capacity of RC structures. However, most of existing studies neglect the uncertainties involved in the structures, e.g., geometric size and material properties, while it may have great influence on the overall behavior of the structure under progressive collapse. In this paper, a probabilistic analysis of RC beam-column sub-assemblage under column removal scenario is performed. An efficient numerical model based on the finite element software OpenSEES is firstly developed for progressive collapse analysis of RC structures. The model adopts fiber beam-column element with co-rotational formulation to simulate the extreme behavior of frame members under column removal scenario, and uses a Min-Max material to apply the material failure criterion. Then the probability density evolution method (PDEM) is employed to conduct the probabilistic failure analysis. Two benchmark column removal tests of RC sub-assemblages are selected as the numerical case study examples. The deterministic analysis results indicates that the proposed finite element model is effective to reproduce the typical behavior of the sub-assemblages, while the probabilistic analysis provides mean values, standard variations and probability density functions (PDFs) of the whole progressive collapse process. Finally, the influence (or sensitivity) of the uncertain parameters on the global and local behaviors of RC beam-column sub-assemblage under column removal are quantified.

A concise review about fracture assessments of brittle solids with V-notches

A concise review of recent studies about the fracture assessments of elastic brittle solid materials containing V-notches is presented. In this preliminary and brief survey, elastic stress distributions in V-notched solids are discussed first. The concept of notch stress intensity factor is introduced. Combine the digital image correlation method with numerical computation techniques to analyze the stress distribution near the notches. Fracture criteria such as strain energy density, J-integral, theory of critical distance are used. However, various new materials are developed in different engineering fields, thus, the establishment of reliable and accurate material strength theory or failure criterion is imperative. Therefore, predicting fracture for various modern materials would require more experiments to infer material dependent parameters in the local fracture model.

Impact of fuselage cutouts on the stress and deflection behavior: numerical models and statistical analysis

Over the past several years, considerable studies have been made to understand the mechanisms of failure of composite structures and the effect of these mechanisms on the performance of structures components made of composite materials. The compressive response of composite materials has received considerable attention due to their significance in the aerospace industry and the complexity associated with compressive failure. Failure criteria for anisotropic composite materials, which have different strengths in tension and compression, have attracted numerous researchers over decades and it is still today an important research topic. The goal of this study is to create a validated model to evaluate the effect of cutout shape, size, and the lamination angles of layers on the failure criteria of the fuselages. To achieve this objective, finite element method and statistical analysis have been used. The results show that the various analytical and empirical approaches have been used to study the failure capability of the fuselage structure. The model is applicable to the air transport industry. The proposed model has been validated against the known shape of an aircraft.

Modeling of structural failure of Zircaloy claddings induced by multiple hydride cracks

Zirconium alloys have been serving as primary structural materials for nuclear fuel claddings. Structural failure analysis under extreme conditions is critical to the assessment of the performance and safety of nuclear fuel claddings. This work focuses on simulating structural failure of Zircaloy tubes with multiple hydride defects through modeling explicit crack propagation in ductile media. First, we developed an integrated cladding failure model by taking into account both crack initiation induced by hydride/matrix interface separation and ligament tearing-off between activated hydride cracks. Second, to accommodate the initiation, propagation, and coalescence of multiple cracks in finite plastic media we incorporated this structural failure model into a coupled continuous/discontinuous Galerkin (DG) based finite element code, a traditionally preferred implicit numerical framework. Third, to improve the adaptive placement of DG interface elements for crack propagation and to identify potential coalescence of cracks due to the interaction between adjacent hydride cracks, we defined a special failure index for the assessment of potential failure zones using both true plastic strain developed and predicted failure strain based on the Johnson–Cook material failure criterion. Finally, by calibrating the proposed material failure model using a cluster of Zircaloy material experimental tests, we successfully simulated a complete failure process of a fuel cladding tube with multiple hydride cracks.

The effect of tear straps on compressive carrying capacity of composite omega single-stringers

In this paper, the progressive failure analysis method is used to analyze suppression effect and mechanism of tear straps, and study the effect of tear straps with varying coverage on compressive carrying capacity of composite omega single-stringers. Based on ABAQUS, several omega single-stringers with common, half-inclusive and all-inclusive configuration are established. Buckling and post-bucking processes of single-stringers subjected to axial compressive load are analyzed. Hashin failure criterion and Camanho model are adopted, respectively, as the failure criterion and degradation model of materials. Cohesive model is used to simulate the bonding interface. The results show that by strengthening the local stiffness of the stringer and skin, tear straps resist the local buckling deformation and control the occurrence and range of damage induced by local buckling, hence preventing the reduction of the carrying capacity. The all-inclusive configuration is more effective than half-inclusive. The conclusions obtained show that tear straps can improve overall stiffness and load-carrying capacity and the all-inclusive configuration has a higher effect than the half-inclusive configuration. Tear straps play a vital role in improving the carrying capacity of structures.

Fracture plane based failure criteria for fibre-reinforced composites under three-dimensional stress state

Fracture plane based failure criteria for fibre-reinforced composite materials under three-dimensional stress state are presented. The failure function is taken as a polynomial expansion in terms of the stress components on fracture plane, which provides a general mathematical technique for constructing Mohr’s fracture hypothesis-based criteria. The polynomial expansion is then truncated at the quadratic terms to approximately describe the failure function. Besides the basic strengths of UD laminates, the fracture plane angles under transverse tension/compression and pure shear are introduced to calibrate the failure criteria, since Mohr’s concept can be described completely and exactly only by both the basic strengths and the fracture plane angles. According to experimental evidences, the interaction between matrix-dominated and fibre-dominated failure modes is also considered in the present study. No empirical or artificially defined parameters are included in the criteria. Experimental verification for different kinds of unidirectional composites under various stress states demonstrates that the proposed failure criteria have a good predictive ability.

General mixed mode I/II failure criterion for composite materials based on matrix fracture properties

The available mixed mode I/II fracture failure criteria for orthotropic materials have been proposed mostly for cracks along fibers. The important fracture parameter in these criteria is the mode I fracture toughness that can be derived by utilizing standard tests. Whenever the crack is not along the fibers, the prediction of mode I fracture toughness is impossible due to mode mixity. Therefore, a comprehensive criterion that can predict the crack initiation instance has not been proposed so far. In this study, in line with the definition of equivalent fracture toughness for off-axis orthotropic materials, a general mixed mode I/II fracture failure criterion is proposed, which is independent of the orthotropic fracture properties. As per this criterion, it is assumed that the fracture occurs in the isotropic matrix and it is the effect of the fibers modeled as tensile or shear reinforcements. On the other hand, only elastic and fracture properties of the isotropic matrix are included in the proposed criterion, which can be derived easily by simple standard experimental tests. In providing this general criterion, the strain energy release rate approach was considered. The concept of crack initiation and propagation energy is employed for investigating the wasted energy in the fracture process zone due to toughening micro-mechanisms. Moreover, comprehensive experimental tests and the required finite element simulations are performed for validation of the proposed criterion.

A stable and convergent Lagrangian particle method with multiple nodal stress points for large strain and material failure analyses in manufacturing processes

This paper presents a new Lagrangian particle method for the simulation of manufacturing processes involving large strain and material failure. The starting point is to introduce some stabilization terms as a means of circumventing the onerous zero-energy deformation in the Lagrangian particle method. The stabilization terms are derived from the approximate strain vector by the combination of a constant and strain derivatives, which leads to a multiple nodal stress points algorithm for stabilization. The resultant stabilized Lagrangian particle formulation is a non-residual type that renders no artificial control parameters in the stabilization procedure. Subsequently, the stabilized formulation is supplemented by an adaptive anisotropic Lagrangian kernel and a bond-based material failure criterion to sufficiently prevent the tension instability and excessive straining problems. Several numerical examples are presented to examine the effectiveness and accuracy of the proposed method for modeling large strain and material failure in manufacturing processes.

Failure criterion for PA12 SLS additive manufactured parts

In order to use selective laser sintering to manufacture structural parts for automotive and aerospace applications, the failure conditions of such a component must be understood and predicted. A 3D failure criterion for anisotropic materials that incorporates stress interactions is implemented to predict failure of selective laser sintered parts manufactured using polyamide 12 powder. Special test specimens that capture tensile, compressive and shear strengths, as single or combined loads, were designed, manufactured and tested. Results show that significant differences exist between tensile and compressive strengths, and that failure of additive manufactured parts is strongly influenced by the interaction between stresses. The test data shows an excellent fit with a tensor based failure criterion that includes interaction strength tensor components, thus being able to capture the strength behavior of SLS printed components under complex loading conditions. The study also demonstrated that work is still required to allow incorporation of some important stress interactions present in those complex stress fields.

Blast loading of bumper shielded hybrid two-core Miura-ori/honeycomb core sandwich plates

We analyze transient elasto-plastic deformations of two-core sandwich plates with and without a bumper and subjected to blast loads with the objective of ascertaining the energy dissipated due to plastic deformations. The facesheets and the core are assumed to be made of a high strength steel modeled as an isotropic material that obeys the von Mises yield criterion with linear strain hardening. It is first shown that considering a material failure criterion and deleting failed elements does not noticeably affect the energy dissipated in a sandwich plate. Subsequent analyses of two-core structures with and without a blast shield ignore the material failure and assume facesheets to be perfectly bonded to the core. The nonlinear transient problems have been numerically analyzed with the commercial finite element software, ABAQUS/ Explicit. Four different two-core sandwich plates obtained by varying locations of the Miura-ori and honeycomb cores are considered. Results without a shield indicate that using a Miura-ori core beneath the topmost facesheet dissipates more energy for moderate blast loads, while a combination of a honeycomb and a Miura-ori core has the least facesheet deflections. The effects of using a blast shield or a bumper, at a fixed standoff distance from a honeycomb-Miura sandwich panel, is studied by ensuring that the shield and the sandwich structure combination has the same areal density as the sandwich panel without the shield. It is found that for a given blast load, using the shield significantly reduces the energy dissipated in the sandwich panel, the bottom facesheet maximum centroidal deflection and the maximum plastic strain in the cores when compared with equal-weight panels without a shield. For the same energy dissipation, the structure with a blast shield has approximately 42% less weight than that without the shield.

Experimental investigation of reciprocally supported element (RSE) lattice honeycomb domes structural behaviour

The honeycomb configuration of the many Diamatic dome patterns available is particularly convenient for reciprocally supported element (RSE) transformation. This is due to there being only three lattice bar elements intersecting at any apex, irrespective of the number of the bar elements used to form the crown polygon. RSE transformation effort therefore is both reduced and simplified compared to some RSE forms. To inform the understanding of the structural behaviour of honeycomb RSE lattice domes, a study comparing structural modelling predicted behaviour with monitored behaviour in the laboratory was carried out. This investigation focused on the structural behaviour of a RSE lattice honeycomb dome structure under applied static loading. The first part of the study included configuration processing, structural modelling and analysis. The second part involved manufacture, construction and monitored behaviour of the dome in the laboratory. The creation of the selected RSE honeycomb lattice structure together with the structural modelling and experimental outputs are presented and discussed. Predicted displacements and stresses are compared under varying applied loading, boundary support conditions and connection stiffnesses. The locations of the onset of local yielding is considered and discussed. The applied loading did not exceed the tube yield stress according to the von Mises ductile material failure criterion indicating that the dome behaviour observed was elastic.

A novel triaxial failure model for adhesive connections in structural glass applications

Structural adhesive connections for glass applications have been widely investigated in the past years, because of their enhanced mechanical performance when compared to bolted connections. However, due to the lack of established design methods and failure criteria, laboratory tests must always be performed, when adhesive connections are used in real-world structural applications. Because of the above, this work presents the analytical development of a Generalized Triaxial Model (here called GTM) that describes a novel failure criterion for adhesive materials in structural glass applications. This is done developing a generalized triaxial model defined over the three-dimensional stress space, which accounts for the non-linear effects of strain rate and temperature variation. The main output of this work is a five-dimensional formulation that allows to account for a generic stress state by a governing equation expressed as a function of the three-dimensional stress tensor. Both deviatoric and hydrostatic energetic components are taken into consideration by means of a non-linear function of the two contributions. The governing equation is represented in the stress space by a revolution surface that is axial-symmetric with respect to the hydrostatic axis, thus independent of the third stress invariant. The proposed model is suitable for isotropic materials and it is here applied to SentryGlas and TSSA, two adhesive materials used in structural glass applications, for which extensive test campaigns have been performed but for which no failure criteria are available yet in literature. Firstly, the proposed model is analytically compared to other existing general failure criteria. It is shown that some of the existing models that can be found in literature can be seen as a particular case of the proposed model. Then, the model is compared with the experimental results under different loading conditions, strain rates and temperatures. The results are found to be in line with the model predictions for both materials. Additional tensile-torsion tests are also performed to validate the proposed model at varying values of the hydrostatic angle.

Femoral fracture load and fracture pattern is accurately predicted using a gradient-enhanced quasi-brittle finite element model

Nonlinear finite element (FE) modeling can be a powerful tool for studying femoral fracture. However, there remains little consensus in the literature regarding the choice of material model and failure criterion. Quasi-brittle models recently have been used with some success, but spurious mesh sensitivity remains a concern. The purpose of this study was to implement and validate a new model using a custom finite element designed to mitigate mesh sensitivity problems. Six specimen-specific FE models of the proximal femur were generated from quantitative tomographic (qCT) scans of cadaveric specimens. Material properties were assigned a-priori based on average qCT intensities at element locations. Specimens were experimentally tested to failure in a stumbling load configuration, and the results were compared to FE model predictions. There was a strong linear relationship between FE predicted and experimentally measured fracture load (R2 = 0.79), and error was less than 14% over all cases. In all six specimens, surface damage was observed at sites predicted by the FE model. Comparison of qCT scans before and after experimental failure showed damage to underlying trabecular bone, also consistent with FE predictions. In summary, the model accurately predicted fracture load and pattern, and may be a powerful tool in future studies.

Experimental and numerical investigation of material failure criterion with high-strength hull steel under biaxial stress

The loads, stress and strain state of the ship structures are quite complicated under the condition of collision and grounding. The failure criteria which are commonly used in numerical simulations of ship collision have limitations in evaluating the failure characteristics of hull steel under complicated stress. Based on the shell theory, complex stress in plate is simplified as plane stress. In experiments, six different shapes of specimens were designed to study the failure characteristics of high-strength hull steel under biaxial stress. The specimens were pressed with a hemispherical indenter until destruction under quasi-static loading. The displacement of specimens’ midpoint and loading force were recorded. The simulation models which considering the mesh size sensitivity and the failure criteria combined with the damage evolution model have been studied. A new reasonable formula is proposed to calculate the average failure strain of different mesh size. With the application of the average failure strain, a bilinear damage evolution model for high strength hull steel in biaxial tension stress is established. Based on a plastic instable criterion, a modified BWH (m-BWH) criterion is proposed. The comparison of Constant strain (CS) criterion combined with linear damage evolution model, the BWH and m-BWH failure criteria which are combined with the bilinear damage evolution model has been performed in the simulations by Abaqus user material subroutine (VUMAT). Although the BWH criterion is more precise than the constant strain criterion in comparison with the experiment results, its errors will increase with rising of strain ratio. The m-BWH criterion improves the accuracy of the simulations when the strain ratio is high.