International Journal of Mechanics and Materials in Design

The transformation field analysis (TFA) proposed by Dvorak et al. in a sequence of papers in the 1990s is an important conceptual cornerstone of the elastic–plastic analysis of heterogeneous materials. However, the need for highly discretized unit cells required to attain converged homogenized response using finite-element based calculation of the plastic influence matrices employed in TFA simulations has given rise to further developments, including the recent nonlinear TFA approach. This variant leverages characteristic plastic modes that arise in elastic–plastic heterogeneous materials. Herein, we re-visit the TFA approach in the context of periodic materials with large phase moduli contrast, and first quantify the unit cell discretization required to attain the same level of convergence as with full unit cell finite-element based analysis. Subsequently we demonstrate that the finite-volume based calculation of strain concentration and plastic influence matrices requires substantially smaller unit cell discretizations to achieve the same degree of macroscopic and microscopic level accuracy, resulting in large execution time reductions and fewer parameters that describe the underpinning plastic deformation mechanisms. Further reductions may be achieved by explicitly leveraging plastic field localization that assumes distinct spatial distributions or characteristic modes.

Nelder–Mead (NM) and Quasi-Newton (QN) optimization methods are used for the numerical solution of crack identification problems in elastodynamics. Fracture is modeled by the eXtended Finite Element Method. The Newmark-β method with Rayleigh damping is employed for the time integration. The effects of various dynamical test loads on the crack identification are investigated. For a time-harmonic excitation with a single frequency and a short-duration signal measured along part of the external boundary, the crack is detected through the solution of an inverse time-dependent problem. Compared to the static load, we show that the dynamic loads are more effective for crack detection problems. Moreover, we tested different dynamic loads and find that NM method works more efficient under the harmonic load than the pounding load while the QN method achieves almost the same results for both load types.

This paper investigates the effects of discrete layer transverse shear strain and discrete layer transverse normal strain on the predicted progressive damage response and global failure of fiber-reinforced composite laminates. These effects are isolated using a hierarchical, displacement-based 2-D finite element model that includes the first-order shear deformation model (FSD), type-I layerwise models (LW1) and type-II layerwise models (LW2) as special cases. Both the LW1 layerwise model and the more familiar FSD model use a reduced constitutive matrix that is based on the assumption of zero transverse normal stress; however, the LW1 model includes discrete layer transverse shear effects via in-plane displacement components that are C 0 continuous with respect to the thickness coordinate. The LW2 layerwise model utilizes a full 3-D constitutive matrix and includes both discrete layer transverse shear effects and discrete layer transverse normal effects by expanding all three displacement components as C 0 continuous functions of the thickness coordinate. The hierarchical finite element model incorporates a 3-D continuum damage mechanics (CDM) model that predicts local orthotropic damage evolution and local stiffness reduction at the geometric scale represented by the homogenized composite material ply. In modeling laminates that exhibit either widespread or localized transverse shear deformation, the results obtained in this study clearly show that the inclusion of discrete layer kinematics significantly increases the rate of local damage accumulation and significantly reduces the predicted global failure load compared to solutions obtained from first-order shear deformable models. The source of this effect can be traced to the improved resolution of local interlaminar shear stress concentrations, which results in faster local damage evolution and earlier cascading of localized failures into widespread global failure.

Friction Welding is a variation of pressure welding method. Though some experience has already been accumulated in the industrial application of friction welding, achieving the optimal processing parameters is still a difficult task. This work is putting a step forward to achieve the best possible design. This paper presents an investigation on the optimization and the effect of welding parameters on multiple performance characteristics (tensile strength and the metal loss) obtained by friction welded joints. A plan of experiments based on the Taguchi method was designed. The output variables were the tensile strength and metal loss of the weld. These output variables were determined according to the input variables, which are the Heating Pressure (HP), Heating Time (HT), Upsetting Pressure (UP) and Upsetting Time (UT). The main objectives of this study are maximization of tensile strength and minimization of metal loss. By statistical analysis, an optimal level of combination of processing parameters is achieved. To validate the optimization, experience were conducted at optimum parameters.

A Zener–Stroh crack can nucleate at the interface of a multi-layered structure when a dislocation pileup is stopped by the interface which works as an obstacle. During the entire fracture procedure of a crack, Zener–Stroh crack mechanism controls the initial stage, or the first phase of crack initiation and propagation. In our current research, stress investigation on a Zener–Stroh crack initiated at the interface of a thin film bonded to a half plane substrate has been carried out. With the application of dislocation-based fracture mechanics, the micro crack is simulated by the distributed dislocations along the crack line. To eliminate the contradictory oscillation phenomenon for the stress field near the interfacial crack tip, a contact zone behind the crack tip is introduced. The physical problem is thus formulated into a set of non-linear singular integral equations. Through careful examination of the crack singularities at the crack tips for different configurations, the formulated integral equations are solved with numerical methods developed in our research. The contact zone length, the stress fields near the crack tip and the stress intensity factors of the crack are evaluated accordingly. Numerical examples based on practical engineering structures are provided to discuss the influence of the key parameters, such as the thickness of the film, and the Dundurs constants, on the fracture behaviour of the crack.

In this paper, the solid isotropic material with penalisation (SIMP) method for topology optimisation of 2D problems is reformulated in the non-uniform rational BSpline (NURBS) framework. This choice implies several advantages, such as the definition of an implicit filter zone and the possibility for the designer to get a geometric entity at the end of the optimisation process. Therefore, important facilities are provided in CAD postprocessing phases in order to retrieve a consistent and well connected final topology. The effect of the main NURBS parameters (degrees, control points, weights and knot-vector components) on the final optimum topology is investigated. Classic geometric constraints, as the minimum and maximum member size, have been integrated and reformulated according to the NURBS formalism. Furthermore, a new constraint on the local curvature radius has been developed thanks to the NURBS formalism and properties. The effectiveness and the robustness of the proposed method are tested and proven through some benchmarks taken from literature and the results are compared with those provided by the classical SIMP approach.

This article aims to utilize IsoGeometric analysis (IGA) and Level set method for topology optimization of elastoplastic plane stress problems. The IGA is employed to model geometry of the problem and calculate unknown displacements by satisfying equilibrium for materially-nonlinear problems. The von Mises elastoplastic material behavior model with and without isotropic strain hardening is utilized. The normal velocity is derived by the pointwise gradient based sensitivity analysis of the Level set function and the control net is updated at each optimization iteration. The reaction–diffusion equation is also employed to update the design variables, which eliminates the signed distance function dependency, and the algorithm provides capability of hole nucleation. The objective is to maximize the toughness of structure, which is defined as the total external work within a specified displacement, while certain amount of material in the design domain is used. In order to demonstrate the ability and efficiency of the proposed method, several numerical examples are presented.

Công trình hiện tại nghiên cứu về các tính chất ablative và nhiệt của một loại nhựa epoxy đã được sửa đổi bằng các hạt nano titanium dioxide có kích thước khác nhau. Các mẫu đã chuẩn bị được đưa ra nhiệt độ trên 1900 °C và được kiểm tra về tính năng bảo vệ nhiệt và tính năng ablative. Ảnh hưởng của các thành phần composite epoxy đến tính năng bảo vệ nhiệt và tính năng ablative: nhiệt độ tối đa ở mặt sau, và lượng mất mát trung bình dưới điều kiện dòng nhiệt cường độ cao cũng như phân bố nhiệt độ trên bề mặt ablation của mẫu bằng cách sử dụng camera nhiệt và pyrometer đã được thiết lập. Một phân tích thống kê của các kết quả thử nghiệm đã được thực hiện. Kết quả xác nhận rằng nhựa epoxy liên kết chéo với chất đóng rắn polyaminoamide và được sửa đổi bằng TiO2(21 nm) và TiO2(100 nm+1% Mn) cho thấy tính năng bảo vệ nhiệt tốt hơn so với ma trận epoxy không được sửa đổi.

In the present study, an attempt is made to present the governing equations on the post-buckling of two-dimensional (2D) FGP beams and propose appropriate optimization procedure to achieve optimal post-buckling behavior and mass. To this end, Timoshenko beam theory, Von-Karman nonlinear relations, virtual work principle, and generalized differential quadrature method are considered to derive and solve governing equations and associated boundary condition (Hinged–Hinged) for an unknown 2D porosity distribution. Proposed method is validated using the papers in the literature. The optimization procedure including defining porosity distributions (interpolations), post-buckling function and Taguchi method is then proposed to optimize the post-buckling path and minimize the mass of the 2D-FGP beams. Results indicate that, great improvement can be achieved by optimizing the porosity distribution; for an identical mass, the post-buckling paths of optimum points are closer to desired path (dense structure). The difference between uniform and non-uniform porosity distributions is more (58% higher post buckling function), at higher values of the mass. Optimum distributions mostly have the higher values of porosity at center line of the beam and minimum values at outer line. Analysis of variance is also provided to create a better understanding about design points contributions on the post-buckling path.