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Parameter optimization and compressive property of the TC31 titanium alloy X‑type lattice structure by the superplastic forming/diffusion bonding process

Wu Dipeng, Chen Minghe, Fan Ronglei, Xiao Wenchao, Wu Yong

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 2

art. no. e137, 2023

EN

The superplastic forming and diffusion bonding (SPF/DB) process was investigated for the manufacture of the TC31 titanium alloy X-type lattice structure. The finite element (FE) model was used to simulate the SPF process and compression behavior of the X-type lattice structure, and the deformation and compression failure modes were analyzed. A theoretical model was revised to predict the structural compressive strength. The results showed that the material processed by heat treatment still had great plasticity with the maximum elongation of 142.5% at 920 °C. The bonding rate, thinning rate and shear strength of the TC31 alloy joint bonded at 920 °C/3 MPa/60 min were 97.1%, 5.56% and 364 MPa, respectively, which indicated it was suitable for the X-type lattice truss structure to formed in the process parameter. Based on the result of the fundamental test and FE simulation, the X-type lattice structure could be fabricated by DB at 920 °C/3 MPa/60 min and SPF at 920 °C with a target strain rate of 0.001 s-1. Thickness measurements indicated that the area with a maximum thinning rate of 32.9% was located at the transition filet between the bonding areas and the ribs. The surface compressive strength of the X-type lattice structure was 1.51 MPa with a relative density of 0.015 when rib width was 5 mm, and the rib plastic buckling was considered as the failure mode of the TC31 titanium alloy lattice structure formed by SPF/DB. The surface compressive strength of the simulation results is 1.59 MPa with an error of 5.3%. The decrease of material properties and rib local thinning affect the accuracy of the theoretical predictions, and the revised theoretical result is 1.52 MPa with an error of 0.7%.

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Bi-axial stress state hot bulging behavior and plane-stress visco-plastic material modelling of TA32 sheets

Peng Heli, Luo Zhiqiang, Qu Shuguang, Shi Wenzhan, Fu Kunning, Xiao Wenchao, Zheng Kailun

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no e167, 2023

EN

Bi-axial state is the dominant stress state experienced by the sheet metal during various forming processes, which requires a thorough understanding and modelling for process designs. In this paper, effects of equal bi-axial stress-state on the hot deformation behavior of titanium alloys are thoroughly investigated using hot bulging tests, and is further compared to the uniaxial stress state. Firstly, a specific hot bulging test device enabling a uniform temperature field and constant control of strain rate was established, using which, systematic hot bulging tests at various temperatures (750–850 °C) and strain rates (0.001–0.1 s−1) of the near-alpha phase TA32 sheets were conducted to determine the hot equal bi-axial bulging behavior. Based on the testing data of force and geometry variations of bulged domes, the equivalent stress–strain curves were calculated. Secondly, a plane-stress visco-plastic plane-stress model of near-alpha TA32 sheets was developed for the first time, enabling both the uniaxial and biaxial flow behavior and forming limits to be precisely predicted. The prediction accuracies for uniaxial and biaxial cases are 93.5% and 89%, respectively. In the end, the uniform deformation resulting from the strain and strain rate hardening was determined, which contributes to the understanding of the stress-state effect on hardening preliminarily. The plane stress visco-plastic model provides an efficient and reliable material model for finite element (FE) simulations of hot forming titanium alloy sheets.

3

Constitutive modeling of softening mechanism and damage for Ti–6Al–4V alloy and its application in hot tensile simulation process

Yang Xiaoming, Wang Baoyu, Zhou Jing, Xiao Wenchao, Feng Pengni

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

479--491

EN

In this paper, a unified viscoplastic constitutive model for Ti–6Al–4V alloy coupling with damage and softening mechanisms was established to predict the flow behaviors and damage evolution in hot tensile process. To obtain the flow behaviors of Ti–6Al–4V alloy, the hot tensile tests were performed at temperatures between 750 °C and 850 °C and strain rates of 0.01–1 s−1. Then the evolution of microstructure was investigated by scanning electron microscope (SEM) under hot tensile conditions. Otherwise, the macro-fracture morphology of the tensile specimen was observed by SEM. The flow stress and microstructure evolution were predicted based on the set of constitutive model. The constitutive model was embed in ABAQUS by coding a user-defined material subroutine. The results show that the flow stress increases with the temperature decreasing and the strain rate increasing. By comparing the experimental and calculated results, the flow stress and damage evolution can be accurately predicted by the constitutive model. The fracture due to damage can be well predicted by the simulation model, indicating the good predictability of the constitutive model.

4

A physically based constitutive model of Ti-6Al-4 V and application in the SPF/DB process for a pyramid lattice sandwich panel

Wu Yong, Wu Dipeng, Ma Jia, Xiao Wenchao, Zheng Kailun, Chen Minghe

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

366--382

EN

The physically based constitutive modeling, simulation and experimental of a superplastic forming and diffusion bonding (SPF/DB) process were studied for the manufacture of a pyramid lattice Ti-6Al-4 V sandwich panel structure. The high-temperature deformation behaviors of Ti-6Al-4 V were studied using uniaxial tensile tests at various temperatures 860 – 950 °C and strain rates 0.0001 s−1 ~ 0.01 s−1, corresponding microstructures were observed using optical microscope (OM) and Electron Backscattered Diffraction (EBSD). Based on obtained flow behavior and microstructure, a set of physically based constitutive equations of the Ti-6Al-4 V was established and used to simulate the superplastic forming for a pyramid lattice sandwich panel. The thinning ratios, dislocation densities, grain sizes and damage distributions of the sandwich panels were successfully predicted by the finite element (FE) simulation. A pyramid lattice Ti-6Al-4 V alloy sandwich panel with good dimensional accuracy and mechanical properties was manufactured by the SPF/DB process at 920 °C with a gas loading path of 0.0005 MPa/s. The maximum thickness thinning ratio, damage factor and relative grain size at the ribs of the sandwich panel were 26.3%, 6.7% and 0.94, respectively. The established constitutive model aids the FE simulations of SPF/DB manufacture of sandwich panels’ structure enabling both macro- and micro-properties to be synergistically controlled and guides the practical process optimizations.

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Experimental characterization of heat transfer coefficients for hot stamping AA7075 sheets with an air gap

Xiao Wenchao, Zheng Kailun, Wang Baoyu, Yang Xiaoming

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

429--438

EN

The heat transfer coefficient (HTC) is critical for hot stamping and in-die quenching. The air gap at interface is a dominant factor affecting the HTC, which is normally resulted from initial tooling clearance and thinning of deformed aluminum sheet. To precisely determine the HTCs under different air gaps, this research performed a comprehensive investigation on determining HTCs between an AA7075 blank and H13 tool steel. Hot stamping experiments were performed with different air gaps enabling HTC values were determined. Using the experimentally calibrated HTC, a finite-element model for hot stamping a door beam was established, which was successfully verified using the experimentation. The good predictions showed the reliability of the HTC values under different air gap conditions.

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Behaviors and modeling of thermal forming limits of AA7075 aluminum sheet

Xiao Wenchao, Wang Baoyu

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 1

134--143

EN

The aluminum hot stamping process has been widely studied to produce lightweight parts in automobile industry. As forming limit of aluminum sheet at elevated temperatures plays a vital role in judging stamping formability, this study aims at experimentally investigating the forming limits and establishing a constitutive model to predict them. In this study, isothermal deformation test (Nakajima test) of AA7075 was conducted to determine its forming limits at temperatures of 300–450 °C and stamping speeds of 13–40 mm/s. Based on the experimental results, a constitutive model considering continuum damage mechanics was established to predict the forming limits under different deformation conditions. It was found that the formability of the material is best at 400 °C, and a higher strain rate can improve formability slightly. The comparisons between model predictions and experimental results were evaluated; results indicated a good prediction accuracy of the model in describing forming limits of AA7075 at elevated temperatures. Moreover, comparison between different studies on the thermal forming limits of AA7075 was discussed in detail.