International Journal of Material Forming

It is worthy to investigate how it will affect the parameters calibration using an average stress state variable before the practical application of a ductile fracture criterion. In order to study this problem, ten notch specimens of AA7075-T6 sheet were designed to implement the tension tests and a parallel simulation of each test was run to obtain the variation of related variables such as stress triaxiality, Lode parameter and fracture strain. The Lou-Huh criterion was selected to research the prediction error through the difference between the damage value calculated by integral expression and that calculated by analytical expression. Based on the error analysis method, a clear answer was given on how to choose the tension tests of notch specimens in the calibrating process of fracture parameters. The studying results show that the stress state variation of notch specimens has a significant influence on the calibration result. It turns out that how to choose specimens from the ten notch specimens to calibrate the fracture parameters also has big influence on the result. Therefore, it is necessary to conduct an error analysis after the calibration of fracture parameters. Based on the error analysis results, the fracture parameters of AA7075-T6 sheet were optimized and its forming limit diagram (FLD) was deduced based on the optimized parameters. The predictive result of FLD is safe compared with the experimental forming limit results.

This paper in particular deals with the integrated modeling of a pultruded NACA0018 blade profile being a part of EU funded DeepWind project. The manufacturing aspects of the pultrusion process are associated with the preliminary subsequent service loading scenario. A 3D thermo-chemical analysis of the pultrusion process is sequentially coupled with a 2D quasi-static mechanical analysis in which the process induced residual stresses and distortions are predicted using the generalized plane stain elements in a commercial finite element software ABAQUS. The temperature- and cure-dependent resin modulus is implemented by employing the cure hardening instantaneous linear elastic (CHILE) model in the process simulation. The subsequent bent-in place simulation of the pultruded blade profile is performed taking the residual stresses into account. The integrated numerical simulation tool predicts the internal stress levels of the profile at the end of the bending analysis. It is found that the process induced residual stresses have the potential to influence the internal stresses arise in the structural analysis.

In this work, we discuss the derivation and the numerical implementation of a finite strain material model for plastic anisotropy and nonlinear kinematic and isotropic hardening. The model is derived in a thermodynamic setting and is based on the multiplicative split of the deformation gradient in the context of hyperelasticity. Introducing the socalled structure tensors as additional tensor-valued arguments, plastic anisotropy can bemodelled by representing the yield surface and the plastic flow rule as functions of the structure tensors. The evolution equations are integrated by a recentlydeveloped form of the exponential map that preserves plastic incompressibility and uses the spectral decomposition to evaluate the exponential tensor functions in closed form. The model has been validated based on experimental data and its applicability for earing prediction has been demonstrated by performing simulations of cylindrical cup drawing and comparisons with experiments.

The paper shows a new method for three-dimensional bending especially of profiles. The bending process only works in one plane according to the machine geometry. To leave the two-dimensional bending plane, the profile cross-section is turned by an overlaid torsional moment. By this process very long symmetrical and asymmetrical profiles can be bent three-dimensionally without surface damage and the unwanted torsion of asymmetrical profiles can be prevented by means of a similar compensation moment. The paper focuses on the bending method which is realized in the new experimental setup. The device consists of a hybrid machine design of hydraulic and electrical drives, both numerically controlled. The new device realizes a new roll-bending method that uses 6 transportation rolls and also a roll-based bending head. The bending moment is applied in the profile by a transverse force driven by the bending head and a servohydraulic cylinder. The turning of the cross-section during the process is realized by a special machine design, making it possible to turn the guiding rolls and the bending rolls of the machine synchronistically.

During the production of multi-base propellants, in order to identify both the optimal and safety conditions to be used at processing these rubber-like compounds, its rheological behaviour is considered as a key factor. Thus, an analysis of their rheological moduli at the end of the mixing stage and prior to the non-continuous extrusion (ram extrusion) is required so as to predict the optimum parameters to be assumed for both the mixing and extrusion processes. The rheological analysis of this multi-base propellant is carried out by means of a DHR-1 rotational rheometer of TA Instruments, and the complex modulus is proposed as a generalized indicator of the rheological response of these special materials. The complex interrelations among the main parameters of the extrusion process (steady extrusion pressure and extrusion ram velocity) together with the rheological properties of these multi-base propellants, will serve to deduce useful technical guidelines for improving the manufacturing system productivity, safety processing conditions and final product quality.

The paper is linked to the investigation of lubricants for massive hot forging. It was observed temperature range of 200-470°C and screw press was used for tests. The research on friction has been done for Al-Mg and Al-Cu-Mg-Fe-Ni aluminium alloys. In this connection, physical and numerical investigation of friction are performed. On the basis of the ring upsetting technique, the effect of temperature on the friction factor value has been investigated. The regressions for the relationship between friction factor and temperature for all lubricants under study have been obtained. Moreover, the sets of calibration curves were drawn. Each set of calibration curves corresponds to the definite type of aluminium alloy as well as definite conditions of deformation. Some practical recommendations were given.

In the original publication of this paper, an incorrect image of Figure 3 was used in error.