Study on the Tensile Strength in X-Cor Sandwich by Using Finite Element Method

The three-dimensional (3-D) variation of stresses of the single lap joint (SLJ) made from hard steel and epoxy (AV119) under tensile loading is studied using 3-D FE (finite element) analysis. The peel (tension) stress, direct shear (in-plane shear) stress and transverse shear (out-of-plane shear) stress are the responsible for opening (mode-I), sliding (mode-II) and tearing (mode-III) mode of failures, respectively, are computed in the overlap region of the joint. Thin adhesive layer used to join the upper (lap) adherend and the lower (strap) adherend is modelled by surface to surface contact elements. The nonlinear material properties of adhesive and adherend (stress and strain graph obtained from the experiments) are input to the finite element programme. The results show that the variations of peel stress and shear stresses in the overlap region are very complicated in nature and hence a 3-D FE analysis is recommended to have a clear visualisation of these stress variations. The peel stress among all the failure-inducing stresses at the overlap ends are dominant and important for adhesive bonded joint as adhesives are weaker than the stronger adherends. The results of the 3-D FE analysis of the SLJ are in good agreement with the experimental results. This research work is may be considered as detail study of the stress distributions in the vulnerable region of the joint under tensile loading.KeywordsSingle lap jointStructural adhesive bondingHard steelFE analysisAdhesion failureVCCT

The effects of process parameters on the formability of the deep drawing of rectangular cups made of SUS304 stainless steel were investigated by both the finite element analysis method and the experimental approach. A statistical analysis was employed to construct an orthogonal chart which reflects the effects of the process parameters and their interactions on the formability of rectangular cup drawing. The material properties and the forming limit diagram (FLD) of SUS304 stainless steel were obtained from the experiments conducted in the present study and were employed by the finite element simulations. In the finite element analysis, the strain path that led to fracture in the drawing process was examined and the failure modes caused by different process parameters were also identified. With the help of statistical analysis, a formability index for the deep drawing of SUS304 stainless steel rectangular cups was constructed and the critical value of the formability index was determined from the finite element simulation results. The actual drawing processes of rectangular cups were also performed in the present study. The validity of the finite element simulations and the formability index were confirmed by the good agreement between the simulation results and the experimental data. The formability index proposed in the present study provides a convenient design rule for the deep drawing of SUS304 stainless steel rectangular cups.

Reinforced concrete slabs supported on columns fail by punching when a conical plug of concrete perforates the slab above the column. This failure has been mostly investigated experimentally, so what can numerical simulation contribute to understand this phenomenon? To answer this question, a computational simulation tool based on the finite element method is developed. This numerical model is implemented into a computer code in applying the object-oriented programming concept. The requirements that the numerical model should fulfill are derived from a review of the experimental results published in the literature and obtained in our laboratory. The numerical model reproduces the non-linear material behavior characterizing reinforced concrete structures by decoupling the actions of steel reinforcement and concrete. The steel reinforcement is represented by uniaxial truss elements which follow a bi-linear stress-strain response. The concrete is modeled with continuum elements which are described at the constitutive level within the framework of the incremental flow theory of plasticity. The concrete triaxial strength is delimitated with a new failure criterion. A plastic flow rule is derived so as to reproduce the evolution of the plastic strain observed experimentally. Cracking induces strain-softening which refers to a gradual decrease in tensile strength with increasing deformations. The reduction of the tensile strength is controlled by an isotropic decohesion process which is monitored by constant fracture energy. The stiffness degradation due to cracking is reproduced with an isotropic elastic damage model. A perfect bond between concrete and steel is assumed. The capabilities of the numerical model are illustrated by simulating the localized shear failure in soil under a footing, the uniaxial tensile, and the confined compressive tests in plain and reinforced concrete specimens. The simulation of punching failure is investigated for three circular reinforced concrete slabs. The comparison with experimental results indicates that: (1) the punching failure mechanism –characterized by a localized inclined punching crack– is generated, (2) the value of the punching load is predicted, (3) the cracking sequence is reproduced, (4) the global response is slightly too stiff. For slabs with orthogonal reinforcement, the perfect bond hypothesis does not allow to capture the punching failure mechanism and the numerical model is improved by relaxing this hypothesis. The developed computational simulation tool reproduces the punching failure observed experimentally and is consequently used to investigate the failure mechanism. First, it is shown that the punching crack results from a crack coalescence phenomenon at the top of the slab followed by a crack propagation in the direction of the corner slab-column. Second, a condition for punching failure to occur is determined. Third, it is illustrated that the size-effect observed experimentally is reproduced and is reflected by a modification of the tensile stress distribution along the punching crack. Finally, a parametric study of the punching failure is performed revealing that punching failure is governed by the tensile strength of concrete. It is also shown that increasing the percentage of reinforcement raises the punching load and reduces the ductility of failure. Lastly, the computational simulation tool allows to demonstrate that in a circular slab, the applied bending moment is not determinant for the value of the punching load.

Finite element modeling of bolted connections in thin-walled stainless steel plates under static shear

The crush tests for seven specimens of square tubes under axial compression are carried out, whose results are compared with the existing theoretical solutions and the empirical formulas with respect to the buckling load, the wavelength of the crushing mode and the mean crushing load. And also the finite element analysis is conducted by using the code developed in the previous report. The obtained results can be summarized as follows : (1) As for the buckling load the existing theoretical as well as the finite element solutions agree well with the experimental results.(2) As for the crushing wavelength the theoretical prediction fails, however, the finite element solutions which minimize the buckling loads are in quantitatively good agreement with the experimental values. The theoretical values given by Wierzbicki which minimize the rigid-plastic solutions for the mean crushing stresses also agree well with the experimental results.(3) As for the mean crushing load there is not a good agreement between the experimental results and the existing rigid-plastic solutions in which the strain hardening is not fully taken into account, while the empirical formula given by Magee et al. using the tensile strength instead of the yield stress has sufficient accuracy in spite of its simple form.(4) The complicated crushing deformations can be successfully simulated by the finite element method. The obtained mean crushing loads are about 25% smaller on the average than the experimental values because of the thick-walled effect, however, there is a good agreement between them from a qualitative point of view.

This paper presents the results of cyclic loading tests on new high-strength concrete (HC) short columns. The seismic performance and deformation capacity of three reinforced high-strength concrete filled Polyvinyl Chloride tube (RHCPVCT) short columns and one reinforced high-strength concrete (RHC), under pseudo-static tests (PSTs) with vertical axial force was evaluated. The main design parameters of the columns in the tests were the axial compression ratio, confinement type, concrete strength, height-diameter ratio of PVCT. The failure modes, hysteretic curves, skeleton curves of short columns were presented and analyzed. Placing PVCT in the RHC column could be remarkably improved the ultimate strength and energy dissipation of columns. However, no fiber element models have been formulated for computing the seismic responses of RHCPVCT columns with PVT tubes filled with high-strength concrete. Nonlinear finite element method (FEM) was conducted to predict seismic behaviors. Finite element models were verified through a comparison of FEM results with experimental results. A parametric study was then performed using validated FEM models to investigate the effect of several parameters on the mechanical properties of RHC-PVCT short columns. The parameters study indicated that the concrete strength and the ratio of diameter to height affected the seismic performance of RHC-PVCT short column significantly.

Through the analysis of X-cor sandwich's microscopic characteristics a finite element model of X-cor sandwich's compressive modulus was proposed. The finite element software ANSYS was used in the computation of compressive modulus. The effects of changing angle, diameter and density on the X-cor sandwich's compressive modulus were analyzed. The numerical analysis results indicate that as the Z-pin's angle increases the X-cor sandwich's compressive modulus decreases, and as the Z-pin's diameter and density increase its compressive modulus increases. Via the analysis of finite model the influencing trends of X-cor sandwich's parameters to its compressive modulus are achieved, the rationality of the proposed finite element model is verified and the finite element model can be used to forecast its compressive modulus.

The effects of static, dynamic and fatigue behavior on three-dimensional shape optimization of hip prosthesis by finite element method

An analytical model was developed to determine the stress and strain distributions of single-lap adhesive-bonded composite joints under tension. Both the adherend and the adhesive were assumed linear elastic in the derivations. The Laminated Plate Theory was used in defining the mechanical behavior of the composite adherends, whereas the linear elasticity theory was applied to describe the material response of the adhesive. By doing so, the stresses in the adhesive can vary through the bondline thickness. After the overall system of governing equations was determined by energy method, it was solved by using a symbolic solver—Maple with appropriate boundary conditions. Results from the analytical model were verified with finite element analysis using commercial software ABAQUS. Single-lap composite joint experiments were conducted following ASTM D3165, Strength Properties of Adhesives in Shear by Tension Loading of Single-Lap-Joint Laminated Assemblies. Although all three failure modes of bonded joints, substrate, cohesive, and adhesive failure, were present as the experimental results, the substrate failure mode was the major failure mode observed. Therefore, only substrate failure mode was analyzed using the developed model in the present paper. Four failure criteria, Tsai-Hill failure criterion, von Mises failure criterion, maximum interlaminar tensile stress criterion, and maximum normal stress criterion, were used to correlate the stresses and failure load. Nonlinear regression was conducted to determine the necessary parameters in the failure criteria. Based on the experimental results, thicker bondlines result in weaker joints. The variation of failure load for joints with various bondline thicknesses was consistent with the predicted results.

Stress analysis and damage evolution in individual plies of notched composite laminates subjected to in-plane loads

Investigation of the effects of allogeneic mesenchymal stem cells on bone union and regeneration in the necrosed bone by biomechanical test and the finite element method

Pulsed laser forming is a non-contact thermal forming process, where sheet metal gets plastically deformed by thermal residual stresses induced by controlled discontinuous laser irradiations. The temperature and deformation fields have been determined using finite element analysis under different processing conditions. Two types of pulsed laser forming processes, i.e., overlapped and discrete spot forming have been identified depending on the combinations of process parameters. Bending angle is found to increase with the degree of overlap and decrease with the increase of gap in case of the two types of spot forming processes. A comparative study between pulsed and continuous laser forming has also been performed using both finite element simulations and experiments. Bending angle in case of discrete spot pulsed laser forming is found to be more compared to the continuous laser forming. The results of finite element simulations have been found to be in good agreement with the experimental results.

The finite element method is a powerful analysis tool which has facilitated a better understanding of the behaviour of reinforced concrete structures. Its use in the research field is widespread and complements experimental tests and the development of new analytical models. Its application in practice engineering has permitted to deal with complex elements. However, the general structural engineer is still reluctant to consider finite element modelling for his work as he finds most of these models excessively sophisticated for his needs and knowledge. In particular, complexity of many finite element tools usually derives from the adoption of advanced concrete constitutive models. Implementation of more simple models based on engineering practice could facilitate its use by less experienced finite element users.\nIn structural engineering practice finite element analysis can be of great usefulness to deal with those more problematic elements and/or where the application of traditional analysis methods presents limitations. This includes the so-called D-regions with a 3D behaviour. The strut-and-tie method and the stress field method are consistent and rational tools for the analysis and design of D-regions, but while their application to 2D elements is well covered in literature, its extension to 3D is problematic. This generally explains why excessively conservative assumptions are still common in the design of these elements. Refinement of current analytical and design approaches or the use of finite element analysis could lead to more rational solutions which in turn will reduce material requirements and costs.\nA 3D nonlinear finite element-based tool was developed in this thesis oriented towards the analysis and design of 3D D-regions by less experienced finite element users. Regarding material modelling, an orthotropic concrete model was adopted to permit the use of uniaxial stress-strain relationships. Only one single parameter, the uniaxial compressive strength of concrete, needs to be defined. Additionally, several aid functions were implemented, among which the following can be highlighted: a comprehensive, embedded reinforcement model to facilitate the introduction of complex rebar geometries; special support and load elements permitting an integrated and simple treatment of the boundary conditions imposed by them; and a simple design algorithm for the automatic determination of the required rebar areas.\nThree examples of applications to representative 3D D-regions are presented to show the capabilities of the tool. In particular, the analyses of fourteen four-pile caps, three socket base column-to-foundations connections and one anchorage block are described in the third part of the thesis. Results prove that realistic response predictions can be obtained considering relatively simple constitutive models. The capacity of the tool to configure consistent stress field models depending on the reinforcement arrangement is also demonstrated. The generation of rational reinforcement configurations by applying the implemented design algorithm is also shown.\nA strut-and-tie-based method for the analysis and design of four-pile caps with rectangular geometries is proposed in the fourth part. The method is based on a refined 3D strut-and-tie model and the consideration of three potential modes of failure: exceeding the reinforcement strength, crushing of the diagonal strut at the base of the column with narrowing of the strut and splitting of the diagonal strut due to transverse cracking. The main innovation is that the strut inclination is not fixed as in current strut-and-tie-based design procedures, but determined by maximizing the pile cap strength. The method accounts for strength softening of cracked concrete, compatibility constraints and reinforcement details. Its application to 162 specimens of literature led to very good predictions of the ultimate strength and, to a lesser extent, of the mode of failure.

The design of electromagnetic devices requires accurate calculation of the design parameters. The finite element method is extensively employed in the design of electrical machines and other electromagnetic and magnetic systems. The finite element method provides an accurate and simple approach to parameters evaluation from the determination of electromagnetic field distribution. The details of designed permanent magnet machines and magnetic couplers are presented. The experimental and finite element simulation results are in good agreement.

Real-world groundwater modeling deals with heterogeneous and anisotropic aquifer systems. Numerical models, particularly the finite difference and finite element methods, are extensively used for modeling such a complex aquifer system. The finite difference method is an age-old straightforward approach, whereas the finite element method is more idealistic, relatively new, and has emerged as a popular approach. The unique advantages with the finite element method are (i) an irregular-shaped domain can be discretized into elements with a matching boundary, (ii) a node can be connected with the neighboring nodes in any direction. Thus, the finite element analysis allows water/solute to flow more freely toward the surrounding nodes along nodal links. On the other hand, the mathematical formulation of the finite element technique follows a set of rules step by step. Conventionally, this idealistic approach uses shape functions and integration techniques to develop element matrices, which, in turn, are assembled to form the global matrix. This conventional global matrix was found to be inconsistent with the basic partial differential equation representing the mass balance in a nodal domain as a control volume. As a result, the matrix solution, particularly for nonlinear problems (e.g., vadose zone flow, density dependent flow, and so forth) becomes unstable and computationally burdensome. To overcome the limitations of the conventional finite element method for real-world groundwater modeling, a new approach, called the direct-formulation finite element (DFFE) method, has been developed. In this approach, a two-dimensional model domain is discretized into triangular elements. Element matrices are formed directly based on flow principles and material properties of elements without using shape functions and integration process. The DFFE method is robust. The global matrix is consistent, and the solution is stable and efficient. The results obtained from this approach were found in a good agreement with that obtained from analytical and other widely used models.