Consistent Integration Schemes Research Articles

Adaptive meshfree method for fourth-order phase-field model of fracture using consistent integration schemes

An adaptive fourth-order phase-field model is proposed using consistent element-free Galerkin method (EFG). Convenient construction of high-order interpolation functions in EFG method is fully utilized. Requirement of C1 continuity of shape functions is satisfied in fourth-order phase-field model. Two different consistent integration schemes with high efficiency and high accuracy, namely quadratically consistent one-point integration scheme and three-point integration scheme, are employed to evaluate the fourth-order phase-field equation and displacement equation, respectively. To reduce computational cost, the adaptive strategy of local background mesh refinement is established on basis of strain energy history and phase field. Background mesh is refined via the insertion of nodes at the midpoints of each side of the integration element. Comparing with EFG method, computational accuracy and efficiency are enhanced by the proposed method. Load-displacement response, the smoothness of the resulting stress and crack paths are predicted well.

A novel mixed and energy‐momentum consistent framework for coupled nonlinear thermo‐electro‐elastodynamics

AbstractA novel mixed framework and energy‐momentum consistent integration scheme in the field of coupled nonlinear thermo‐electro‐elastodynamics is proposed. The mixed environment is primarily based on a framework for elastodynamics in the case of polyconvex strain energy functions. For this elastodynamic framework, the properties of the so‐called tensor cross product are exploited to derive a mixed formulation via a Hu‐Washizu type extension of the strain energy function. Afterwards, a general path to incorporate nonpotential problems for mixed formulations is demonstrated. To this end, the strong form of the mixed framework is derived and supplemented with the energy balance as well as Maxwell's equations neglecting magnetic and time dependent effects. By additionally choosing an appropriate energy function, this procedure leads to a fully coupled thermo‐electro‐elastodynamic formulation which benefits from the properties of the underlying mixed framework. In addition, the proposed mixed framework facilitates the design of a new energy‐momentum consistent time integration scheme by employing discrete derivatives in the sense of Gonzalez. A one‐step integration scheme of second‐order accuracy is obtained which is shown to be stable even for large time steps. Eventually, the performance of the novel formulation is demonstrated in several numerical examples.

A meshfree method with gradient smoothing for free vibration and buckling analysis of a strain gradient thin plate

In this paper, a meshfree Galerkin approach is presented for analysis of free vibration and buckling of a strain gradient thin plate. A cubic moving least square or reproducing kernel approximation with C2 continuity is used to ensure convergence. Due to smoothness of the meshfree approximation, the only variable is the deflection of a thin plate. To improve the computational accuracy, a consistent integration scheme with gradient smoothing is introduced to construct stiffness and geometrical stiffness matrices. The effectiveness of such an approach is confirmed by numerical results, and it is superior to a standard Gauss integration based meshfree Galerkin method. Further, the influence of classical and high order boundary conditions is investigated on the natural frequencies and critical buckling loads of strain gradient thin plates.

Adaptive analysis for phase-field model of brittle fracture of functionally graded materials

Gradient distributions of material properties are taken into account in phase-field model of fracture and the adaptive consistent element-free Galerkin method (EFG) for the fracture analysis of functionally graded materials (FGMs) is presented. Considering the fact that both the moving least-square approximation and the consistent integration scheme contribute to producing the accurate stress fields, the phase-field model of fracture for FGMs is numerically solved by the consistent EFG method in this paper. The corresponding adaptive criterion is established and 2D and 3D crack propagation of FGMs is simulated. Numerical results indicate that the proposed method can accurately reflect the influence of different distributions of material parameters on the crack propagation and has high efficiency compared with the standard EFG method and linear FEM. At some level, the fracture mechanism that crack propagation is driven by both the strain energy history and the critical energy release rate is revealed using phase-field model.

A stable and efficient meshfree Galerkin method with consistent integration schemes for strain gradient thin beams and plates

Abstract The strain gradient (SG) theory, incorporating with thin beam and plate models, can effectively describe size effects of micro- and nano-structures. However, since these models are determined by a sixth-order partial differential equation that requires the C2 continuity of deflection in a Galerkin weak form, it is difficult to make stable and efficient numerical analysis. In this paper, a meshfree Galerkin method is presented for SG thin beams and plates. To satisfy the continuity and convergence requirement, moving least square or reproducing kernel shape functions are employed with cubic approximation bases. To pass the patch test, integration constraints are derived and consistent integration schemes are proposed with nodal smoothed derivatives instead of standard ones on evaluating points. Numerical results show that consistent integration is superior to the standard Gauss integration in convergence, accuracy and efficiency.

Consistent integration schemes for meshfree analysis of strain gradient elasticity

Integration schemes with nodal smoothed derivatives, which meet integration constraint conditions, are robust and efficient for use in meshfree Galerkin methods, however, most of them are focussed on the classical elasticity determined by a second-order partial differential equation. In this paper, arbitrary-order integration constraint conditions are derived for strain gradient elasticity in a fourth-order partial differential equation. These integration constraint conditions provide the discrete forms of nodal shape functions and their first- and second-order derivatives. Furthermore, to meet the integration constraint conditions, consistent integration schemes are designed with nodal smoothed (but not standard) derivatives at evaluating points. It is shown that such nodal smoothed derivatives are able to satisfy the differentiation of approximation consistency. Finally, several case studies are given and the results demonstrate that, based on convergence, accuracy and efficiency, the numerical performance of consistent integration in meshfree analysis of strain gradient elasticity is superior to the standard Gaussian one.

A temperature-based thermodynamically consistent integration scheme for discrete thermo-elastodynamics

The formulation of thermodynamically consistent (TC) time integration methods was introduced by a general procedure based on the GENERIC form of the evolution equations for thermo-mechanical problems. The use of the entropy was reported to be the best choice for the thermodynamical variable to easily provide TC integrators. Also the employment of the internal energy was proved to not involve excessive complications. However, attempts towards the use of the temperature in the design of GENERIC-based TC schemes have so far been unfruitful. This paper complements the said procedure to attain TC integrators by presenting a TC scheme based on the temperature as thermodynamical state variable. As a result, the problems which arise due to the use of the entropy are overcome, mainly the definition of boundary conditions. What is more, the newly proposed method exhibits the general enhanced numerical stability and robustness properties of the entropy formulation.

Time integration of a model for martensite detwinning and reorientation under nonproportional loading using Lagrange multipliers

The paper presents a consistent integration scheme for a model of shape memory alloys that takes into account the processes of detwinning and reorientation of martensite. Lagrange multipliers are used to account for the saturation condition on the martensitic phase, which expresses the requirement on the inelastic deformation of martensite not to exceed a material-specific value. A detailed procedure for implicit time integration of the constitutive equations is given, including a comprehensive derivation of a closed-form expression for the consistent tangent moduli. The equations are implemented into a commercial finite element software, which is used to simulate the response of martensitic SMA structures to complex loading. The results are shown to agree with experimental data taken from the literature.