Experimental and Numerical Research on Deformation Behavior of Thin-Walled and Large Expansion Ratio Guide Vane Liner in Hydroforming Process

Some tube hydroforming process tests and further research work were conducted to manufacture hollow guide vane liners( made of super alloy GH3030).The relative thickness( t0/ OD) of the tubular blank is approximately 0. 01,and the maximum expansion ratio( Dmax/ OD) of the needed part is more than 40%,and the length to diameter ratio of the expansion regionis more than 3. 0. It is very hard to manufacture this kind of ultra-thin-wall,curved axis and large expansion ratio tubular part without fracture and wrinkles. The success of the process is highly dependent on useful wrinkles with appropriate internal pressure and axial feeding. A simplified finite element model and a theoretical model are used for detecting the deformation behavior and forming laws. Further study results demonstrate that the useful wrinkles do not appear at the same time and middle-wrinkles need bigger axial force than tube-end-wrinkles and feeding-wrinkles. The wrinkles can transfer bigger axial force after its wave peak has come into contact with the die inner surface. The thickness thinning rate of the element at the peak is bigger than that at the trough. With the increase of the axial and hoop stress ratio,the critical buckling stress also increases. Microstructure examination results show that the grain size in the maximum thinning zone has been stretched and refined after the large deformation and annealing treatment.The process is feasible and the finished part is qualified.

Effect of Loading Paths on Hydroforming Tubular Square Components

The influence of loading path on tube hydroforming process is discussed in this paper with finiteelement simulation. Four different loading paths are utilized in simulating the forming process of square tubular component with hydroforming and the result of different loading path is presented. Among the result. the thickness distribution of bilinear loading path is the most uniform one. It shows that the increase of punch displacement in the stage of high pressure is beneficial to the forming of component for optimized Stress condition.

Numerical Simulation of Failure during Cylindrical Cup Hydrodynamic Deep Drawing

In this paper, a method to combine the mathematical analytic equation and general FEM software has been applied in the simulation of hydrodynamic deep drawing (HDD) cylindrical cup, also the failure types such as fracture and wrinkling are studied and solved. The simulated results are coincided with experimental results.

Hot deformation behavior and strain compensation constitutive model of equiaxed fine grain diffusion-welded micro-duplex TC4 titanium alloy

In this work,two-stage diffusion bonding of micro-duplex TC4 titanium alloy was car-ried out to study the flow behavior and constitutive models of the bonding joint and the base metal after the same thermal cycling during the hot forming process.Microstructure and mechanical properties test were used to verify the good quality of the equiaxed fine grain diffusion-welded TC4 alloy.Quasi-static tensile experiment was carried out at temperatures ranging from 750–900℃and strain rates of 0.0001–0.1 s^(-1).The joint showed the weak dynamic recovery at strain rates of 0.01–0.1 s^(-1)and temperatures of 750–850℃.At strain rates of 0.0001–0.001 s^(-1)and tempera-tures of 850–900℃,the flow stress of joint presented steady-state characteristics.Different defor-mation conditions lead to the remarkable difference of dynamic softening performance between the joint and heat-treated base metal,but the flow stress in elastic and strain hardening stages exhibited similar behavior.The strain compensated Arrhenius-type constitutive models of TC4 joint and heat-treated base metal were developed respectively.The fifth-order polynomial functions between the material property correlation coefficients and strain were obtained.The models have shown good correlation,with correlation coefficient values of 0.984 and 0.99.The percentage average absolute relative error for the models were found to be 10%and 9.46%,respectively.

A visco-elastoplastic constitutive model of aircraft polymethylmethacrylate related to strain rate and temperature

The visco-elastoplastic mechanical behavior related to the applied strain rate and temperature around the glass transition temperature of Polymethylmethacrylate(PMMA)has been systematically investigated.The uniaxial tensile test was performed at strain rate and temperature rangs 1.0×10^(-4)-1.0×10^(-2)s^(-1)and 363-393 K,respectively,and the Dynamic Mechanical Analysis(DMA)test was carried out between 363 K and 413 K at various frequencies.Moreover,the robust complex constitutive model considering the temperature and strain rate effect is proposed.A nonlinear viscoelastic model is established to describe the viscoelastic response on the basis of the Zhu-Wang-Tang(ZWT)model and the time temperature equivalence principle,including the dependence of strain rate and temperature.Considering the yield stress,the cooperative model is adopted.The viscoplastic mechanical response is manifested as the competition performance of the softening deformation and hardening behavior.The predicted mechanical responses maintain good consistency with the experimental results,indicating that the visco-elastoplastic constitutive model proposed can accurately predict the mechanical behavior of PMMA materials within the imposed strain rate and near the glass transition temperature range.

Design of an innovative multi-stage forming process for a complex aeronautical thin-walled part with very small radii

In this paper, an aeronautical thin-walled part with a complex geometry which has several sharp bends and curvatures in different directions was investigated. This kind of part is difficult to be manufactured only in one stage. Therefore, an innovative multi-stage active hydroforming process assisted by the rigid forming method was designed. In addition, an optimized blank geometry is obtained. In fact, the main focused point of this paper is to propose a new small radius rounded corner forming technique and analyze the mechanism. Two kinds of forming modes of changing a big rounded corner into a small one, which are related to different tangential positions of the die in the process of calibration, are analyzed theoretically. Meanwhile, the stress and strain states of the deformation region are compared. The relationships between the minimum relative radii of rounded corners I and II in the first stage and the hydraulic pressure are calculated by the bending theory. Finally, the influences of the tensile-bulging effect and the interface condition of the double-layer sheet on the forming quality of the specimen are investigated. The achieved results can make a foundation for utilizing the proposed method in forming of thin-walled parts with very small radii.

An inverse strategy to determine constitutive parameters of tubular materials for hydroforming processes

This paper is to determine the flow stress curve of 5049-O aluminium alloy by a tube hydraulic bulging test with fixed end-conditions. During this test, several tubular specimens are bulged under different internal pressures before their bursting, and the corresponding bulging height and wall thickness at the pole are measured. An inverse strategy is developed to determine the constitutive parameters of tubular materials based on experimental data, which combines the finite element method with gradient-based optimization techniques. In this scheme, the objective function is formulated with the sum of least squares of the error between numerical and experimental data, and finite difference approximation is used to calculate the gradient. The tubular material behavior is assumed to meet the von Mises yield criterion and Hollomon exponential hardening law. Then, constitutive parameters identification is performed by minimization of the objective function. In order to validate the performance of this framework, identified parameters are compared with those obtained by two types of theoretical models, and tensile tests are performed on specimens cut from the same tubes. The comparison shows that this inverse framework is robust and can achieve a more accurate parameter identification by eliminating mechanical and geometrical assumptions in classical theoretical analysis.