Use of A True Material Constitutive Model for Stress Analysis of A Swage Autofrettaged Tube Including Asme Code Comparison

This work reports a new finite element analysis (FEA)-based user programmable function (UPF) featuring true material constitutive behavior with proper algorithms for accurate stress analysis of swage autofrettage of high-strength thick-walled cylinders. The material constitutive model replicates an existing Bauschinger-effect characterization (BEC). This incorporates elastoplastic material behavior during loading. Reversed loading includes a reduced elastic modulus and nonlinear plasticity resulting from the Bauschinger effect (BE), both depend upon the maximum level of loading plastic strain. Swage autofrettage case studies identify the difference in stress distributions based on different material models: a bilinear isotropic material model, a bilinear kinematic hardening model, and the user defined model that features the BEC. Development and integration of such a UPF into a standard FEA package is a crucial unresolved and fundamental modeling issue relating to re-yield, fatigue and fracture of modern swaged cylinders and pressure vessels. It will not only provide a fundamental understanding of the deformation mechanics of the tube during the swage autofrettage process and ensure optimal process parameters are achieved, but also provide guidance for material selection, design and optimization of the manufacturing processes for high intensity cylindrical parts, a potential multibillion-dollar market. Near-bore residual stresses for the BEC case are noteworthy and reported in detail, e.g., axial residual stress is tensile and hoop residual stress exhibits a distinct slope reversal, unlike hydraulic autofrettage, indicating the possible need to re-assess the ASME Pressure Vessel Code (correction for BE) regarding swage autofrettage.

Research on Deformation Mechanism of Cutting Nickel-Based Superalloy Inconel718 Based on Strain Gradient Theory

The traditional material constitutive model can effectively simulate the mechanical properties during the cutting process. However,the scale characteristics contained in materials are not considered in traditional cutting model, and the inherent scale effect of materials are also ignored. Therefore, the traditional cutting constitutive model cannot effectively reflect the size effect in cutting process, and then cannot obtain the accurate stress, strain and temperature. In this present paper, a material constitutive model which can reflect the scale effect is established based on the strain gradient plasticity theory. Through the established model and secondary development of ABAQUS, the two-dimensional dynamic Finite Element Simulation model of cutting Inconel 718 is established. By comparing the cutting experiment results with the simulation results, the established simulation model can more accurately reflect the effects of temperature, strain gradient effect, equivalent stress and its scale effect on cutting deformation during the machining process.

Significance of material constitutive model and forming parameters on the crashworthiness performance of capped cylindrical tubular structures

An accuracy of crushing performance indicators is critical to evaluate in finite element crushing simulations particularly for the press-formed capped tubular energy absorbing structures. It is essential to select the appropriate material constitutive model and to incorporate the forming parameters into the finite element crushing model as a vital input. Hence in the present article, the influence of various material constitutive models and forming (multi-stage deep drawing) parameters on the axial crashworthiness characteristics of thin-walled capped cylindrical tubes were investigated numerically. Both forming and crushing simulations were executed by nonlinear finite element LS-DYNA® code. The forming parameters such as thickness distribution, residual stress, and effective plastic strain were mapped to a finite element crushing model of the tube. The numerical predictions of the thickness distribution and final deformed profiles of the capped cylindrical tubes are correlated with the experiments. The results revealed that the forming parameters have a substantial effect on the crushing performance of the deep drawn capped cylindrical tubes. As a result of these analyses, the thickness and strain predictions strengthens the tube and significantly influenced the crushing performance indicators such as initial peak crushing force, mean crushing force, and the energy absorbing capacity.