Development of LSTM networks for predicting viscoplasticity with effects of deformation, strain rate and temperature history

In this paper, long short-term memory (LSTM) networks are used in an original way to model the behavior of a viscoplastic material solicited under changing loading conditions. The material behavior is dependent on history effects of plasticity which can be visible during strain rate jumps or temperature changes. Due to their architecture and internal state (memory), the LSTM networks have the ability to remember past data to update their current state, unlike the traditional artificial neural networks (ANNs) which fail to capture history effects. Specific LSTM networks are designed and trained to reproduce the complex behavior of a viscoplastic solder alloy subjected to strain rate jumps, temperature changes or loading-unloading cycles. The training datasets are numerically generated using the constitutive viscoplastic law of Anand which is very popular for describing solder alloys. The Anand model serves also as a reference to evaluate the performances of the LSTM networks on new data. It is demonstrated that this class of networks is remarkably well suited for replicating the history plastic effects under all the tested loading conditions.

Key Techniques in Simulating Comprehensive Anchor Behaviors by Large Deformation Finite Element Analysis

With the application of innovative anchor concepts and advanced technologies in deepwater moorings, anchor behaviors in the seabed are becoming more complicated, such as 360 deg rotation of the anchor arm, gravity installation of anchors with high soil strain rate, and keying and diving (or penetration) of anchors. The anchor line connects the anchor and the anchor handling vessel (AHV) or floating moored platform. With moving of the AHV or platform, anchor line produces a space movement, and forms a reverse catenary shape and even a three-dimensional (3D) profile in the soil. Finite element analysis on the behaviors of anchor lines and deepwater anchors requires techniques that can deal with large strains and deformations of the soil, track changes in soil strength due to soil deformation, strain rate and strain softening effects, appropriately describe anchor–soil friction, and construct structures with connector elements to conform to their characteristics. This paper gives an overview of several key techniques in the coupled Eulerian–Lagrangian (CEL) analysis of comprehensive behaviors of deepwater anchors, including construction of the embedded anchor line and the anchor line in the water, installation of gravity installed anchors (GIAs), keying or diving of drag anchors, suction embedded plate anchors (SEPLAs) and GIAs, and implementation of the omni-directional arm of GIAs. Numerical probe tests and comparative studies are also presented to examine the robustness and accuracy of the proposed techniques. The aim of this paper is to provide an effective numerical framework to analyze the comprehensive behaviors of anchor lines and deepwater anchors.

Key Techniques in Simulating Comprehensive Anchor Behaviors by Large Deformation Finite Element Analysis

With the application of innovative anchor concepts and advanced technologies in deepwater moorings, anchor behaviors in the seabed are becoming more complicated, such as 360-degree rotation of the anchor arm, gravity installation of anchors with high soil strain rate, and keying and diving (or penetration) of anchors. As a very important component of the installation or mooring system, anchor line connects the anchor and the anchor handling vessel (AHV) or floating moored platform. With moving of the AHV or platform, anchor line produces a space movement, and forms a reverse catenary shape and even a three-dimensional profile in the soil. Numerical analysis on the behaviors of anchor lines and deepwater anchors requires techniques that can deal with large strains and deformations of the soil, track changes in soil strength due to soil deformation, strain rate and strain softening effects, appropriately describe anchor-soil friction, and construct structures with connector elements to conform to their characteristics. Being an effective tool of large deformation finite element analysis, the coupled Eulerian-Lagrangian (CEL) method is advantageous in handling geotechnical problems with large deformations, where a traditional Lagrangian analysis is coupled with an Eulerian phase of material advection. This paper gives an overview of several key techniques in the CEL analysis of comprehensive behaviors of deepwater anchors, including construction of the embedded anchor line and the anchor line in the water, installation of gravity installed anchors (GIAs), keying or diving of drag anchors and GIAs, and implementation of the omni-directional arm of GIAs. Numerical probe tests and comparative studies are also presented to examine the robustness and accuracy of the proposed techniques. The aim of this paper is to provide a numerical framework to analyze the comprehensive behaviors of anchor lines and deepwater anchors.

Modelling of Recrystallization Curves of Porous Copper-Titanium Powder Materials

In this paper, modelling and plotting of recrystallization curves of copper-titanium powder materials with titanium content of 0.5%, porosity 5% and 10%. The mathematical model that describes an influence of temperature, degree of deformation, strain rate, initial grain size and porosity to grain size after deformation has developed. The interconnection of deforming parameters and structure has presented by function of several variables with analytical expression obtained by method of undetermined coefficients based on experimental data. Theoretical recrystallization curves for copper-titanium powder materials with different porosity have plotted. It has established that porosity decelerates the kinetics of structure formation during dynamical softening of porous powder materials.

Superplastic Behavior and Constitutive Equation of AZ31B Magnesium Alloy

To study the superplasticity of AZ31B magnesium alloy, hot compression tests were performed in forming temperature range from 280°C to 440°C and strain rate range from 0.001s-1 to 0.1s-1. The influence of deformation strain rate and forming temperature on flow stress was also analyzed detailed. It was shown that the flow stress of AZ31B was very sensitive to formpng temperature and stain rate, and was decreased with deformation temperature increasing, and was increased with stain rate increasing. However, no significant change of flow stress was observed at the temperature of 440°C and the strain rate below 0.01s-1. The activation energy of AZ31B in superplastic deformation was 141.6KJ•mol-1 and its constitutive equation was established also.

Study on Impact Crushing Properties of High Strength Steel Sheets

The purpose of this study is to verify the validity of sheet buckling design based on the effective width theory investigation of impact crushing properties in high strength steel sheets. We clarify the need to make full sections effectively without elastic buckling occurring and consider the application of the effective width theory under high speed deformation. We report our findings of our investigation into the sheet buckling phenomenon with numerical simulation by varying deformation strain rate, mechanical property of material and member configuration. The results demonstrate that, with increasing crush speed, the cross section of a steel sheet become effective, while there is a high possibility of the buckling phenomenon that does not function as efficient impact absorption and is not evaluated with the existing theory.

The Superplastic Deformation and Microstructural Analysis of Fine-Grained 1420 Al-Li Alloy

The superplasticity of fine-grained 1420 Al-Li alloy which was prepared by two-stage aging and turning rolling process was studied by constant-strain-rate tensile test. The results showed that: good superplasticity was attained at temperature range of 460°C~520°C and deformation strain rate 1×10-4s-1~5×10-3s-1. An elongation of 650% was obtained at the temperature of 650°C and strain rate of 1×10-4s-1. Furthermore, the microstructures of material before and after deformation were examined using OM and TEM. Equiaxed grains were still kept, and the second-phase particles and dislocations were observed in the deformed samples.