Hoffman Failure Criteria Research Articles

SUGGESTIONS FOR IMPROVEMENTS IN TIMBER PORTAL FRAME DESIGN WITH SEMI-RIGID KNEE JOINTS

Timber portal frames assembled on the construction site are the most suitable solution from the point of view of limitations of transportation options. However, the connections of the rafters and columns assembled at the construction site in the knee joints, using bolts, show a certain tendency to show plastic deformations under load. In addition, the transmitted shear forces at the knee joint form different angles with the fiber direction in the rafter and column elements. Service experience of timber portal frames shows that the vertical displacement of the apex point increases, also cracks appear in the rafter elements near the knee joints over time. Unfortunately, code design formats do not present specifications for timber structures incorporating L-shape joints with mechanical fasteners. This article presents the results of studies that confirm the need to supplement the design rules for wooden portal frames. It is recommended to implement the rotational spring constant when define rigidity of L-shape joints for RFEM model of structure. The Hoffman failure criterion has been chosen as the most appropriate of the known ones for evaluating the crack resistance of structural wooden elements, because this criterion includes more important specific properties affecting the development of plastic deformations and the formation of cracks in wood.

Topology optimization for additive manufacturing with strength constraints considering anisotropy

Abstract Combining topology optimization and additive manufacturing (AM) is a promising approach to breaking through the limitations of conventional design and developing innovative structures with high performance. However, the unique manufacturing constraints in AM should be considered when developing the topology optimization algorithms for AM. Material anisotropy is one of the common characteristics of AM materials due to the layer-by-layer manufacturing techniques. This work proposes a topology optimization approach for AM with strength constraints considering anisotropy. The Hoffman failure criterion is adopted to represent the anisotropic strength behaviors of AM materials. Based on the Hoffman failure criteria and the p-norm measure aggregation function, a global strength constraint formulation is established. Under the framework of solid isotropic material with penalization, we develop a topology optimization methodology to minimize the structural weight or volume fraction subject to structural stiffness and strength constraints. Several two-dimensional (2D) or 3D numerical test cases are performed to validate the effectiveness and performance of the developed method. The results indicated that the proposed method could make full use of material properties by considering anisotropic strength. Besides, the topological optimization considering strength anisotropy could be combined with build direction optimization to further reduce the structural weight.

Examining agreement between finite element modelling methodologies in predicting pathological fracture risk in proximal femurs with bone metastases

BackgroundFinite element modelling methodologies available for assessing femurs with metastases accurately predict strength and pathological fracture risk which has led them to being considered for implementation into the clinic. However, the models available use varying material models, loading conditions, and critical thresholds. The aim of this study was to determine the agreement between finite element modelling methodologies in assessing fracture risk in proximal femurs with metastases. MethodsCT images of the proximal femur were obtained of 7 patients who presented with a pathologic femoral fracture (fracture group) and the contralateral femur of 11 patients scheduled for prophylactic surgery (non-fracture group). Fracture risk was predicted for each patient following three established finite modelling methodologies which have previously shown to accurately predict strength and determine fracture risk: non-linear isotropic -based model, strain fold ratio -based model, Hoffman failure criteria -based model. FindingsThe methodologies demonstrated good diagnostic accuracy in assessing fracture risk (AUC = 0.77, 0.73, and 0.67). There was a stronger monotonic association between the non-linear isotropic and Hoffman -based models (τ = 0.74) than with the strain fold ratio model (τ = −0.24 and − 0.37). There was moderate or low agreement between methodologies in discriminating between individuals at high or low risk of fracture (κ = 0.20, 0.39, and 0.62). InterpretationThe present results suggest there may be a lack of consistency in the management of pathological fractures in the proximal femur based on the finite element modelling methodologies.

Study on dynamic modeling of composite thin cylindrical shells subjected to low-velocity impact based on an analytical method

<p indent="0mm">Aiming at the problems of traditional finite element modeling with many black box operations, high computational costs, and no independent intellectual property rights, this paper establishes a fiber-reinforced composite under low-speed impact excitation based on the first-order shear deformation theory, the Von Kamen large deformation theory and the law of conservation of energy. Analytical model of impact characteristics of cylindrical shells under the fixed-supported boundary at both ends. By considering the impact delamination damage and the Hoffman failure criterion, the expression of impact contact force when each failure event occurs is deduced. Therefore, the impact contact force and load-displacement curves are successfully solved, with a feasible analysis process of low-velocity impact property being summarized. Finally, the proposed model are validated against the Abaqus finite element model with different laminate configuration and impact velocities being considered. It can provide a new idea and approach for predicting and evaluating the impact dynamics of other complex cylindrical shells with anisotropic characteristics.

Multi-objective design optimization of 3D micro-architected implants

Recent advances in 3D printable micro-architected materials offer unprecedented possibilities for the development of highly tailored orthopaedic implants. These devices, which are typically made from fully solid materials, significantly alter load transmission to the surrounding bone tissue, potentially leading to interface instability and bone resorption. In this work, we present computational methods to synthesize three dimensional (3D), patient-specific, implants with heterogeneous micro-architecture. Our method simultaneously minimizes the risks of load-induced interface fracture and peri-prosthetic bone remodelling, while taking into account functional and manufacturing constraints.We first develop a novel parametric micro-architecture with desirable functional attributes and a wide range of effective mechanical properties, including both positive and negative Poisson’s ratios. We then present formulations which optimize the spatial configuration of micro-architecture parameters in order to simultaneously minimize the risk of load-induced interface fracture and post-operative bone remodelling. To that end, a novel bone remodelling objective is devised, taking into account both bone apposition and resorption, predicted via a model based on strain–energy density. The interface fracture objective is defined as the maximum value of the multi-axial Hoffman failure criterion along the interface.The procedure is applied to the design of 3D titanium hip implants with prescribed conventional geometries and compared, in silico, to both a conventional solid implant and a homogeneous low-stiffness lattice design. The optimized implant results in a performance improvement of 64.0% in terms of bone remodelling, and 13.2% in terms of interface fracture risk, compared to a conventional solid implant design.

Numerical and Experimental Analysis of Timber Portal Frame with Semi-Rigid Knee Joints

The problems related to development of rotational deformations of a knee joints and crack propagation in rafter elements of timber portal frames were discussed in this article. The rotational displacement, which develops between the rafter and column members due to the bending deformations of the bolts in the knee joint with a simultaneous embedment into the wood, increases the global deformations of the portal frame. Additionally, to axial force and bending moment the rafter elements are heavily loaded with shear force at the sections near knee joint especially. All effects together create very complicated complex of affecting factors. In the current study the design methodology of timber portal frames has been revised with the purpose to develop a more comprehensive set of design conditions for timber portal frames with dowel type fasteners in the knee joints. It is suggested to use the Hoffman failure criterion taking into account the difference of strength in tension and compression to manage the effects of plastic yielding combined with the crack development in wood assumed it as an orthotropic material. It has been proved by case studies of timber portal frames under service loads, as well as by tests and theoretical considerations. The set of design conditions must be supplement by additional clauses comprising Hoffman failure criterion regarding timber sections heavily loaded in shear and cross grain tension. Also, it is recommended that the design capacity of dowel type fastener should be decreased when shear force transferred by the bolt acts perpendicular to the grain direction inducing tension cross grain direction. Other measure may be application of some surface strengthening method.

Detection and numerical simulation of blasting-induced damage in shallow-buried twin tunnels with small spacing

In order to study the damage effect of blasting load on the surrounding rock of shallow-buried small spacing twin tunnels, the shallow-buried tunneling section of the south extension project of Shunhe Expressway is taken as the engineering background. Firstly, based on the dynamic damage evolution and Hoffman failure criterion, an anisotropic dynamic damage constitutive model for rock materials is established. Then, by using the secondary development function of the LSDYNA software, the constitutive model is applied to the numerical simulation of the tunnel blasting damage. Finally, based on the acoustic wave measurement theory, the wave velocities in the surrounding rock of the shallow-buried small spacing twin tunnels before and after blasting were measured by using non-metallic ultrasonic detectors, and the damage of the surrounding rock is evaluated from changes in wave velocity. The applicability of the anisotropic dynamic damage constitutive model and the accuracy of the numerical results are verified by comparing the numerical simulation results with the field test results. The numerical simulation results show that the maximum damage radius of single-hole blasting is 0.58 m, and the maximum damage depth is 1.88 m. According to the damage threshold of the rock mass, the horizontal failure range of the rock mass can reach 0.14 m, and the failure depth is 1.70m. According to the field test, the damage degree of the middle intercalated rock is higher than that of the other parts of the surrounding rock in the alternate blasting excavation of the double track tunnel. The damage depth of the surrounding rock caused by blasting excavation is about 0.5 m, which is close to the simulation results, and verifying the accuracy of the anisotropic dynamic damage constitutive model. The research results have a certain guiding role on the blasting excavation and damage control of shallow-buried twin tunnels with small spacing..

Multi-body dynamic model of subject specific knee: Utilization of mri images for reconstruction of contact bodies and insertion sites

The aim of the study is to determine failure of the cemented polyethylene acetabular component, which might occur due to excessive bone resorption, cement–bone interface debonding and fatigue failure of the cement mantle. Three-dimensional finite element models of intact and implanted pelvic bone were developed and bone remodeling algorithm was implemented for present analysis. Soderberg fatigue failure diagram was used for fatigue assessment of the cement mantle. Hoffman failure criterion was considered for prediction of cement–bone interface debonding. Results indicate fatigue failure of the cement mantle and implant–bone interface debonding might not occur due to bone remodeling.

Influence of cancellous bone material and dead zone on stress-strain, bone stimulus and bone remodelling around the tibia for total ankle replacement.

Extreme bone resorption due to bone remodelling is one of the reasons for ankle component loosening. Finite element (FE) analysis has been effectively used nowadays for pre-clinical analysis of orthopaedic implants. For FE modelling, the selection of bone material and dead zone play a vital role to understand the bone remodelling. This study deals with the effects of different cancellous elastic modulus-density relationships and dead zone on bone remodelling around the tibia owing to total ankle replacement (TAR), using finite element analysis with physiological loading conditions. This study also investigated the bone stimulus distribution in the tibia to identify the initial indication of bone density changes due to bone remodelling. Additionally, the Hoffman failure criterion was used to investigate the chances of implant-bone interface failure due to different cancellous bone material modelling and bone remodelling. The present bone remodelling study consists of three different dead or lazy zones (±0.75, ±0.60 and ±0.35) to examine the influence of the dead zone on bone remodelling. Differences in stress/strain distribution were observed in the tibia bone due to different cancellous bone material modelling. Despite little variations, bone density changes due to bone remodelling were found to be almost similar for two FE models having different cancellous bone material. Similar to these results, the effect of different dead zone on bone density changes due to bone remodelling was found to be minimal. Bone stimulus distribution in the cancellous bone was found to be almost similar for FE models having different cancellous bone material modelling and different dead zones. To understand the stress/strain and interface related failure of the tibial component, cancellous bone material modelling plays a crucial role. However, cancellous bone material modelling and dead zone have minimal influence on bone remodelling around the tibia cancellous bone due to TAR.

Progressive damage simulation of open-hole composite laminates under compression based on different failure criteria

The strength prediction of open-hole fibre-reinforced composite laminate under compression is very important in the design of composite structures. The modelling of fibre, matrix damage and delamination plays an important role in the understanding of the damage mechanics of laminate under open-hole compression. In this article, a progressive damage model for open-hole compression that is based on continuum shell elements and cohesive elements is established to model in-plane damage and delamination, respectively. The damage mechanics of sublaminate-scaled laminates with ply sequence [45/0/−45/90]ms and ply-level-scaled laminates with ply sequence [45n/0n/−45n/90n]s are investigated by our proposed model. The Tsai-Wu and Hoffman failure criteria are employed for the determination of matrix damage initiation. Compared with the experiments, the numerical results using the Tsai-Wu criterion exhibit better accuracy regarding open-hole compression strength prediction and failure modes simulation.

Assessment of failure of cemented polyethylene acetabular component due to bone remodeling: A finite element study

The aim of the study is to determine failure of the cemented polyethylene acetabular component, which might occur due to excessive bone resorption, cement–bone interface debonding and fatigue failure of the cement mantle. Three-dimensional finite element models of intact and implanted pelvic bone were developed and bone remodeling algorithm was implemented for present analysis. Soderberg fatigue failure diagram was used for fatigue assessment of the cement mantle. Hoffman failure criterion was considered for prediction of cement–bone interface debonding. Results indicate fatigue failure of the cement mantle and implant–bone interface debonding might not occur due to bone remodeling.

種々の織構造を有する織物複合材料のマルチスケール損傷進展シミュレーション

In this study, a multiscale damage simulation of woven composites with various weaving structures is conducted based on a homogenization theory. For this, the homogenization theory is reconstructed for 2×2 twill-woven laminate and 5H satin-woven laminates. The Hoffman's failure criterion is then introduced into the theory to determine the failure of fiber bundles and a matrix material, and the damage modes. The damages are expressed as reduction of stiffness according to the damage modes. The present method can efficiently analyze the macroscopic strength and the microscopic damage development of woven composites. This method is then applied to the damage simulation of plain/twill/satin-woven E-glass/vinylester laminates under on-axis uniaxial tension. It is shown that the weaving structures affect the macroscopic strength of the laminates, which is attributable to the difference in the microscopic damage development in the laminates depending on the weaving structures.

Mechanical Behavior and Modeling of Dowelled Steel-to-Timber Moment-Resisting Connections

AbstractThis paper investigates the mechanical behavior of dowelled steel-to-timber moment-resisting connections. Two configurations of joints were tested, and the experimental results were used to validate a three-dimensional (3D) nonlinear finite element method (FEM) model. The model uses the Hill criterion to manage the plastic yielding of timber. The brittle character of timber in shear and tension perpendicular to grain is managed through the damage evolution based on the Hoffman failure criterion. The numerical model represents with good accuracy the behavior observed during experiments. The analytical model based on the theory of plastic limit analysis was evaluated through the application to the tested connections.

Failure and Broken Criteria for 2.5D Woven Composites Loaded in Weft

2.5D woven composites has been used broadly. But its failure reason and process has not been researched clearly. To describe whole the tensile process in weft direction exactly, Based on the yield criteria ,yield criteria and elastic mould reduced rule are consummated to analyze the process of yield process; Meantime, Hoffman failure criteria is used to analyze the broken process and the corresponding elastic mould reduced rules is given. FEA method is adopted to simulate and analyze the whole tensile process of 2.5D woven composites in weft load at last. To verify the failure criteria and the corresponding elastic mould reduced rule, weft –tensile tests of six kind of 2.5D composites have been done. Results of contrast show that failure criteria and the corresponding elastic mould reduced rule is very suit for 2.5D woven composites. The whole failure progress for a sample with hole are simulated at the end of this paper.

Stochastic nonlinear failure analysis of laminated composite plates under compressive transverse loading

This paper present the second ordered statistics of first-ply failure response of laminated composite plate with random material properties under random loading. The basic formulation is based on higher order shear deformation plate theory (HSDT) with the geometrically nonlinearity in the von-Karman. The direct iterative based C 0 nonlinear finite element method combined with mean centered first order perturbation technique developed by the authors are extended and successfully applied nonlinearity for failure problem with a reasonable accuracy to predict the second order statistics (standard deviation) of first-ply failure response using Tsai–Wu and Hoffman failure criterion with macroscopic analysis. Typical numerical results for various combinations of boundary conditions, plate thickness ratios, aspect ratios, laminates scheme and layers, elastic modulus ratios have been presented to illustrate the application of developed procedure. Some new results are presented and examined which clearly demonstrated the importance of the randomness in the system parameters in the failure response of the structures subjected to transverse loadings.

Mechanical behavior of GRP pressure pipes with addition of quartz sand filler

In comparison with steel, concrete, and polymeric pipes, glass-reinforced plastic (GRP) pressure pipes use more expensive raw materials. Thus, despite of their attractive structural performance, mainly in terms of mechanical strength combined with low weight, the higher cost can be a limitation in many applications. In this scenario, an alternative to reduce the final price of GRP pipes is the addition of quartz sand filler. In this experimental and numerical study, filament-wound E-glass/polyester pipes with nominal inside diameter of 300 mm and wall thickness of 5.7 mm were produced with the incorporation of quartz sand as filler and tested to failure under internal pressure. The mechanical behavior of the composite pipes was evaluated experimentally, throughout short-time hydraulic failure pressure tests, as well as using finite element analysis (FEA). In the FEA simulations, the shell wall was modeled as an axisymmetric layered orthotropic material. A good agreement, varying from 96% to 98%, was obtained between the average hydraulic failure pressure measured and FEA predicted failure pressures, using Tsai—Hill and Hoffman failure criteria, respectively.

Numerical and experimental analyses of multiple-dowel steel-to-timber joints in tension perpendicular to grain

The behaviour of dowel-type steel-to-timber joints loaded in tension perpendicular to grain is analyzed experimentally and numerically. Two main types of failures are observed in the experiments such as wood splitting and embedding. The experimental results are used to validate a three-dimensional (3D) non-linear finite element model. The non-linear model uses the Hill criterion to control the plastic yielding of wood material. The Hoffman failure criterion, controlling the damage evolution in wood, is used to take into account the brittle failure in shear and tension perpendicular to grain. The comparison with experimental results shows that the numerical results are in good agreement with them. The validated model is used to investigate the effect of some influential parameters on the splitting strength of the joints loaded in tension perpendicular to grain. Besides, the splitting strengths given by the numerical model are used to evaluate the accuracy of some analytical formulae available in the literature.

Numerical 3D finite element modelling and experimental tests for dowel-type timber joints

This study is a contribution to various scientific researches on dowel-type timber joints. In this paper, a three-dimensional (3D) finite element model is developed to predict the mechanical behaviour of steel-to-timber joints loaded in parallel-to-grain tension. The adopted material model is based on the isotropic behaviour of the steel and the transverse isotropy behaviour of the timber. In order to take into account the asymmetric mechanical behaviour of timber material in tension and compression, Hoffman failure criterion is associated with the Hill criterion to control the plastic yielding combined with the damage evolution of timber. Besides, the interaction among materials is modelled using contact elements associated with friction. The results obtained in numerical simulations are evaluated and compared with experimental results. The model showed the capacity to simulate the behaviour of the timber joints. Moreover, an analytical model based on stress interactions is presented to calculate the failure loads of the timber joints.

Modelling of chip separation in machining unidirectional FRP composites by stiffness degradation concept

Progressive failure of unidirectional glass fiber-reinforced polymer composites (FRP) was studied using finite element analysis in orthogonal machining. Chip formation process and damage modes such as matrix cracking, fiber–matrix debonding and fiber breaking were modelled by degrading the material properties. Damage analysis was carried out using Hashin, Maximum stress and Hoffman failure criteria. After damage was detected, selective stiffness degradation was applied to the workpiece material. The objective of this study is to better understand the chip formation process and to analyse the cutting-induced damage from initiation stage until complete chip formation. The effect of the fiber orientation on cutting forces and sub-surface damage was investigated with different failure criteria. The results were addressed in terms of cutting forces evolution and damage progression in the composite structure during machining. It was demonstrated that the use of the stiffness degradation concept with the appropriate failure criterion responds potentially in a predictable fashion to changes in chip formation process for machining of FRPs.

Failure behavior of composite sandwich structures under local loading

Usually when analyzing the mechanical response of foam-cored fiber-reinforced composite sandwich structures to localized static loading, the face sheets are treated as a linear-elastic material and no damage initiation and growth is considered. However, practice shows that at higher indentation magnitudes damage develops in the face sheet in the area of contact with the indentor, which could lead to local failure of the face laminate due to the loss of bending stiffness and strength. Therefore, the main objective of the present study is to develop a damage model for predicting the local failure in the composite face sheet and its influence on the load–displacement behavior of sandwich structures under local loading. For this purpose, the Hoffman failure criterion is incorporated into a finite element modeling procedure using the ABAQUS program system. Results deducted from the modeling procedure are compared with experimental data obtained in the case of static indentation tests performed on sandwich beam specimens using steel cylindrical indentors. It is shown that taking into account the damage in the face sheet leads to a substantial improvement in the performance of the model when simulating the mechanical behavior of the sandwich structures at higher indentation values.