Papers by Author: Jian Ping Lin

Abstract: QP steel has great application potential for automotive industry for its ultrahigh strength and good plasticity. In this paper, the forming limit diagram (FLD) of QP steel was experimentally studied using spherical punch test. The forming limit curves (FLC) of QP steel in room temperature under two pressing velocities (20mm/s, 2mm/s) were obtained. It has been found that the deformation velocity affects the FLC obviously; the FLC declines with the increase of pressing velocity. Compared with other AHSS under the same strength grade, QP steel keeps high strength without a significant loss of plasticity.

Abstract: Several studies and design of cooling systems for hot stamping tools have already been made. The phase transformations which occur during the process are known, and numerical simulations are now very close to the reality [1]. However these studies are often related to a specific part and can hardly be extrapolated to other parts. This paper presents several results based on a thermo-mechanical analysis which can be used to make a first design of a cooling system for hot stamping tool. A theoretical study describes the heat transfer from the tools to the cooling pipes related to different flow parameters. Numerical simulation with the software COMSOL Multiphysics has been carried out to obtain results about cooling rate and maximum stress into the tool against geometry parameters. The heat transfer model used for simulation has been validated through experiment. To finish a data analysis describes the relationship between the different parameters, more specifically their impact on the cooling. With this study we can now determine which pipes’ location and size and flow properties are likely to provide the most efficient cooling system, and which parameter we must modify to optimize it.

Abstract: The bonded structures in vehicles are usually in different enclosure conditions. A finite element (FE) model, based on fluid-solid coupling method, has been established for analyzing the temperature distribution of adhesive single-lapped joint when curing in a closed enclosure. The heat transferring process of the adhesive joint in an exposed environment has also been executed for comparison purpose. The FE temperature results of both joints are validated by experiments. It has been found that the joint temperature in a closed enclosure rises much more slowly compared with the joint in an exposed environment within the curing process. Due to the thickness variation along the adhesive joint, it can be observed on both joints the lap area always obtains the lowest temperature while the joint ends obtain the highest ones.

Abstract: The automotive body system is not only a source for directly radiating noise into the vehicle interior space, but also a key component for transmitting various vibrations and noise. The optimization of the modes for body-in-white has significant meanings for improving the reliability and NVH (Noise, Vibration and Harshness) performance of the whole vehicle. Based on the current situation that there is more severe interior vibration and noise problem occurring in driving for a light passenger vehicle, a hybrid modal analysis method combined with experiment and simulation methods is applied to investigate the vibration and noise characteristics of the whole vehicle body. By performing such modal analysis, the modal frequencies of the auto-body are improved effectively by strengthening the vibration sensitive regions in the body structure. The experiment for measuring interior vibration and noise levels under cruise condition is conducted to validate that the structural optimization for body-in-white has significant contribution for improving the whole vehicle NVH performance.

Abstract: To describe the heat transfer of fully-closed adhesive joint in curing process, adhesive joint, enclosure for closing joints and its inner air are simplified as a multi-lumped-heat-capacity system neglecting the heat from adhesive chemical reaction. Based on heat transfer theory, a temperature prediction model of fully-closed joint was proposed. Combining experimental temperature history of the joint with finite difference method, the combined heat transfer coefficients of adhesive under different curing temperatures were obtained according to Newton's heat transfer formula. And the model was validated by the experiments. The results revealed that the model can be used to predict the temperature of fully-closed adhesive joint in curing process.

Abstract: obtaining the law of stress and strain distribution of loaded adhesive joint has significant implication for joint design and its strength prediction. The dynamic FEM model of uniaxial tensile adhesive joint was established, in which strain fracture criteria is adopted. It can be observed from the FEM results that: lapped area of the joint bears shear stress primarily, the adherend areas located away from the lapped area bear steady tensile stress mainly and the adherend areas adjacent to lapped area endure tensile and shear stress simultaneously. Based on stress distribution characters, the joint was divided into three areas (lapped area, stress transfer area and uniform stress area) and an analytical model predicting the length of stress transfer areas was developed. DIC technology was applied to measure the whole field strain of the joint. It can be seen from the DIC results that the joints area division and the model of predicting the length of stress transfer length are feasible.

Abstract: The parent sheet selection in TWB designing is largely dependant on the effect of parent materials parameters on formability of TWBs. Experiments and FE simulations were performed to study the effect of material parameters of TWB’s parent sheets such as t (thickness ratio), k (strength factor of materials), n (strain hardening index), r (anisotropy index) on LDH and weld-line movement of TWB. Orthogonal experiments and range analysis were used to analyze the sensitivity on effect of different parameter on LDH and weld-line movement. The results show that LDH of TWB decreases with increasing ration of stronger sheets parameters to weaker ones, and the rate decreases gradually; in contrary, weld-line movement increases and the increasing rate decreases gradually. Furthermore, different parameters make various contributions to LDH and weld-line movement of TWBs and the effect degree of each parameter changes with different thickness ratios.

Abstract: The forming of tailor-welded blank is an important technology to body light weighting. While it is difficult to predict the forming limits of tailor welded blanks with different base materials or thickness. For the expanding experiments, an analytical method to predict forming limit height of tailor-welded blanks is established based on the deformation characteristic and plastic theory, and verified by simulation results. This method is not only provided a path to predict forming limit of tailor welded blanks but also provided references to the design of tailor weld parts.

Abstract: Tailor-welded blanks (TWB) have been widely used in automobile industry. In this paper, expanding experiments are carried out for tailor-welded blanks both with curved seams and straight seams, and the formability of tailor-welded blanks with curved seams has been studied and compared with tailor-welded blanks with straight seams. The effects of thickness ratios and seam radius on the formability of tailor-welded blanks with curved seams and straight seams are deduced, separately. In the end, the relationships between the shapes of welding seams and forming heights, and relationships between the thickness ratios and forming heights are given, which are valued to the designers and processers of tailor-welded blanks.

Abstract: With the increasing use of finite element analysis method in sheet forming simulations, springback predictions of advanced high strength steel (AHSS) sheet are still far from satisfactory precision. The main purpose of this paper was to provide a method for accurate springback prediction of AHSS sheet. Material model with Hill’48 anisotropic yield criterion and nonlinear isotropic/kinematic hardening rule were applied to take account the anisotropic yield behavior and the Bauschinger effect during forming processes. U-channel forming and springback simulation was performed using ABAQUS software. High strength DP600 sheet was investigated in this work. The simulation results obtained with the proposed material model agree well with the experimental results, which show a remarkable improvement of springback prediction compared with the commonly used isotropic hardening model.