Mechanical Performance Evaluation of the Al-Mg-Si-(Cu) Aluminum Alloys after Transient Thermal Shock through an Novel Equivalent Structure Design and Finite Element Modeling

In this paper, the microstructure evolution and mechanical performance of the Al-Mg-Si-(Cu) aluminum alloy after transient thermal shock were investigated through experimental tests and finite element simulations. A novel equivalent structure was designed as a typical case in which one side of the plate was welded therefore the other side was thermally shocked with different temperature distribution and duration. The temperature gradient which influences most importantly the mechanical properties was simulated and experimentally verified. Through cutting layers and tensile testing, the mechanical response and material constitutive relation were obtained for each layer. Gurson-Tvergaard-Needlemen (GTN) damage parameters of these samples under large strains were then obtained by the Swift law inverse analysis approach. By sorting the whole welded joint into multi-material composed structure and introducing the obtained material constitutive relation and damage parameters, tensile properties were precisely predicted for typical types of weld joint such as butt, corner, and lap joints. The results show that precipitate coarsening, phase transformation from β″ phase to Q′ phase, and dissolving in the temperature range of 243.3–466.3 °C during the thermal shock induced a serious deterioration of the mechanical properties. The highest reduction of the ultimate tensile strength (UTS) and yield strength (YS) would be 38.6% and 57.4% respectively. By comparing the simulated and experimentally obtained force-displacement curves, the error for the above prediction method was evaluated to be less than 8.1%, indicating the proposed method being effective and reliable.

Modeling of Crack Extensions in Arc-Shaped Specimens of Hydrogen-Charged Austenitic Stainless Steels Using Cohesive Zone Model

Crack extensions in arc-shaped specimens of hydrogen-charged and as-received conventionally forged (CF) 21-6-9 austenitic stainless steels are investigated by two-dimensional finite element analyses with the cohesive zone model. The material constitutive relation is first obtained from fitting the experimental tensile stress-strain data by conducting an axisymmetric finite element analysis of a round bar tensile specimen of the as-received CF steel. The material constitutive relation for the hydrogen-charged CF steel is estimated based on the experimental tensile stress-strain data of the as-received CF steel and the hydrogen-charged high-energy-rate-forged (HERF) 21-6-9 stainless steel. The cohesive zone model with the exponential traction-separation law is then adopted to simulate crack extensions in arc-shaped specimens of the hydrogen-charged and as-received CF steels. The cohesive strength of the cohesive zone model is calibrated to match the experimental load-displacement curve with the cohesive energy determined by the J-integral at the maximum load of the arc-shaped specimen. The computational results showed that the numerical predictions of the load-displacement and crack extension-displacement curves for the hydrogen-charged and as-received CF steel specimens are compared reasonably well with the experimental data.

On the behaviour of spherical inclusions in a cylinder under tension loads

In the present paper the behaviour of a hyperelastic body is studied, considering the presence of one, two and more spherical inclusions, under the effect of an external tension load. The inclusions are modeled as nonlinear elastic bodies that undergo small strains. For the material constitutive relation, a relatively new type of model is used, wherein the strains (linearized strain) are assumed to be nonlinear functions of the stresses. In particular, it is used a function such that the strains are always small, independently of the magnitude of the external loads. In order to simplify the problem, the hyperelastic medium and the inclusions are modelled as axial-symmetric bodies. The finite element method is used to obtain results for these boundary value problems. The objective of using these new models for elastic bodies in the case of the inclusions is to study the behaviour of such bodies in the case of concentration of stresses, which happens near the interface with the surrounding matrix. From the results presented in this paper, it is possible to observe that despite the relatively large magnitude for the stresses, the strains for the inclusions remain small, which would be closer to the actual behaviour of real inclusions made of brittle materials, which cannot show large strains.

Nonlinear Finite Element Analysis for Compressive Capacity of Interior Constrained Square Concrete-Filled Steel Tube Column

Nonlinear finite element model is established for the square interior constrained concrete filled steel tube column based on the research of the element type and material constitutive relation with finite element software ANSYS to find out the influence of the thickness of the steel tube, location of studs and geometry of the stirrups on the compression capacity of the short column, The results show that the compression capacity of the short column has something to do with the thickness of the steel tube and the studs, but the stirrups can eventually enhance a lot for the compression capacity as the validity is confirmed for the coherence of the results stepped from the finite element model and in test.

Local Buckling Analysis of Aluminum I Section Beams

Low elastic modulus of aluminum alloy gives prominence to lateral and local buckling of members, especially when thin walled sections are adopted to save material usage. Under certain conditions of loads and constraint, local buckling would occur in aluminum beams. A numerical study to assess the local stability of aluminum I section beams is presented in this paper. The study focused on two aspects: the local buckling of aluminum flange plate under compression, the local buckling of aluminum web plate under bending and shear. An extensive parameter analysis including width-to-thickness ratio, initial imperfection, material constitutive relation and restriction effect from adjacent plates was carried out with the purpose of extracting several governing parameters and investigating their effects on the local buckling of aluminum plate. Based upon the results of finite element analysis (FEA), a new design method in connection with the local stability of aluminum I section beams has been developed. By virtue of the proposed design method, three key indicators that include the critical value of width-to-thickness ratio to prevent local buckling of aluminum flange plate under compression, the local stability of aluminum web plate under bending/shear and the bearing capacity of aluminum I section beams under the condition that the post buckling strength of web is taken into account, could be obtained to provide more rational and efficient designs. The proposed design method is different from the current Eurocode but acts in accordance with Chinese code for design of steel structures (Chinese steel code) in order to satisfy applicability.

Progress in Theory and Application Research on Microscale Laser Shock Peening

Micro-scale laser shock peening (μLSP) is a novel surface modification technique utilizing mechanical effect of shock wave induced by high intensity pulsed laser with micron spots. μLSP can introduce the beneficial residual compressive stress distribution in surface layers of metal with micron-level spatial resolution, and thus enhance wear resistance and fatigue performances of metallic micro-structures. The characteristics and influence factors of μLSP were briefly introduced, and progress in μLSP research fields was reviewed and presented, including laser induced shock pressure, material constitutive relation, changes of mechanical properties and microstructure evolution of materials. Finally, proposals on further investigations of μLSP were brought forward. The systematical characterization will lay the ground work for better understanding the effect of μLSP in microlength level and developing a more practical simulation method.

Numerical Simulation on Adiabatic Shearing Behavior of Vanadium Alloy V-5Cr-5Ti Hat-Shaped Specimen

In this work, LS-DYNA program was adopted to simulate the loading process of Vanadium Alloy specimen conducted on the Split Hopkinson Pressure Bar (SHPB) in two dimensions. Based on the Johnson-Cook material constitutive relation and criterion of Johnson-Cook failure, the initiation, propagation process of an adiabatic shear band (ASB) and the corresponding distribution of temperature field in the vanadium alloy V-5Cr-5Ti hat-shaped specimen are analyzed. The field of stress, strain and temperature in the tip of an ASB, and the spread speed, the width as well as the type of the ASB are all studied. It is shown that the formation of the ASB is related to the loading velocity and the size of the hat-shaped specimen. And formation of mircocracks and their interlinkage are primary shearing failure mechanism of hat-shaped specimen.

A FEM Study on Chip Formation in Orthogonal Turning Nickel-Based Superalloy GH80A

The nickel-based superalloy GH80A is a typical difficult-to-cut material. It has been used in a good many kinds of aeronautical key structures because of its high yield stress and anti-fatigue performance at high temperature. But selection of cutting parameters in actual machining process mainly depends on experience and lacks of scientific utterance. In this paper, finite element method (FEM) was introduced to study the chip formation process when machining nickel-based superalloy GH80A. By the way of lagrangian finite element approach and material failure, adiabatic shear band (ASB) and periodic fracture were simulated with the help of former researchers’ studies on the material constitutive relation. Both the mechanism of adiabatic shearing phenomenon at primary shear zone and periodic crack in the free surface were analyzed, chip formations under different cutting parameters were got and compared carefully. The root cause of saw-tooth chip formation under different cutting speeds was discussed.

Direct Tensile Performance of UHPCC Element Based on Damage Mechanics

Direct uniaxial tension test of ultra high performance cementitious composites I shape specimens have been investigated in this paper. A nonlinear analytical model based on continuum damage mechanics is developed to characterize tensile stress-strain constitutive response of UHPCC. Basic governing equations of damage evolution and material constitutive relation are established considering random damage which conforms to a modified Weibull type distribution proposed in this paper. Calculation suggests that Weibull distribution can describe damage evolution of UHPCC and predict the constitutive relation and damage evolution equation.