高温变比例双向拉伸试验机测控系统研究

获得金属材料高温条件下的双向拉伸力学性能,是研究超高强钢局部加热变截面辊弯成形机理的前提,以材料热双向拉伸试验的核心需求为背景,研发一套能够获取材料在不同温度、不同加载路径下的力学特性实验设备。通过对比不同的加热方式,最终采用PID控制高频电磁加热方式,实现对试件加热区恒温控制;开发视频引伸计,代替接触式引伸计,检测试件测量区的实时形变量;根据实验要求,基于PID算法,对双向四轴进行速度规划,实现变比例载荷控制。对QP1180超高强钢在350℃下进行7组不同加载比例的双向拉伸试验。对试验结果进行误差分析,温度控制平均误差0. 30%,视频引伸计测量标定误差0. 71%,变比例载荷控制平均误差0. 56%。结果表明,该热双向拉伸试验机方案有效,控制精度达到实验要求,具有一定的工程应用价值。

Finite Element Simulation of Flexible Roll Forming with Supplemented Material Data and the Experimental Verification

Flexible roll forming is a promising manufacturing method for the production of variable cross section products. Considering the large plastic strain in this forming process which is much larger than that of uniform deformation phase of uniaxial tensile test, the widely adopted method of simulating the forming processes with non-supplemented material data from uniaxial tensile test will certainly lead to large error. To reduce this error, the material data is supplemented based on three constitutive models. Then a finite element model of a six passes flexible roll forming process is established based on the supplemented material data and the original material data from the uniaxial tensile test. The flexible roll forming experiment of a B pillar reinforcing plate is carried out to verify the proposed method. Final cross section shapes of the experimental and the simulated results are compared. It is shown that the simulation calculated with supplemented material data based on Swift model agrees well with the experimental results, while the simulation based on original material data could not predict the actual deformation accurately. The results indicate that this material supplement method is reliable and indispensible, and the simulation model can well reflect the real metal forming process. Detailed analysis of the distribution and history of plastic strain at different positions are performed. A new material data supplement method is proposed to tackle the problem which is ignored in other roll forming simulations, and thus the forming process simulation accuracy can be greatly improved.

梯度层含量与应变速率对梯度纳米结构铜变形行为的影响

利用表面机械碾压工艺制备了不同梯度层体积分数的梯度纳米结构铜试样,表征了试样横截面上显微硬度和微观组织的梯度分布特征,对比分析了梯度层体积分数和应变速率对梯度纳米结构铜的力学性能与变形行为的影响。结果表明,随着梯度层体积分数的增加,屈服强度逐渐提高,均匀塑性略有降低,强度与塑性之间出现特殊的"倒置"关系。随着应变速率的逐渐增加,梯度结构金属铜屈服/抗拉强度逐渐上升,均匀延伸率呈缓慢降低趋势:当应变速率从2.0×10^(-4) s^(-1)增加到1.0×10^(-1) s^(-1)时,屈服强度从190MPa上升到220MPa,而对应的均匀延伸率则从15.9%下降为12.1%。

FEM simulation of flexible roll forming based on different material models

Flexible roll forming is a new roll forming process that produces parts with variable cross sections. This forming process is proposed to meet the demand of weight reduction of automobile industry. In order to study the mechanisms and material flow rules in this new forming process,the finite element mothod( FEM) model of a nine-step flexible roll forming of an ultra-high-strength steel bumper is established based on deep understanding and reasonable simplification of the process.Given that the material model is an important factor that influences the simulation accuracy,three material models which consist of different yield criteria and hardening models are adopted in the FEM models. Sheet thickness and springback amount calculated with three material models are studied comparatively. According to sheet thickness reduction and springback amounts,it is found that the MKi( Mises yield criterion and kinematic hardening law) model's result is larger than MI( Mises yield criterion and isotropic hardening law) model and HI( Hill's yield criterion and isotropic hardening law) model. Therefore,it is concluded that material models do have influences on the flexible roll forming simulation and need to be determined carefully.

Yield Loci of TRIP590 Advanced High Strength Steel Based on Biaxial Loading Test

The main purpose of the paper is to obtain the experimental yield loci of TRIP590 advanced high strength steel,and to compare it with the theoretical loci in order to obtain the best yield criterion for this material.First,the biaxial loading tests under different loading paths in the method of load control are carried out.Then,the experimental yield loci of different deformation stages are obtained.Finally,the experimental yield loci are compared with the theoretical loci of Mises criterion and Hill48 criterion,the parameters of which are calculated based on the r?value and the yield stress method,respectively.The results show that the accuracy of the theoretical yield loci of Hill48 based on the yield stress is higher than that of Mises criterion and Hill 48 criterion based on r?value method.

Optimization of yield criterion and simulation based on QP980 high strength steel

QP980 is an ultra high strength steel.First,uniaxial and biaxial tension tests have been done in different loading paths.Then QP980 basic mechanical properties have been obtained.And the stress and strain graph has been drawn.Second,according to the equal principle of the unit volume plastics work and yield stress,QP980 plastic work contour map has been drawn.Third,through comparing Mises,Hill'48,Hosford and Barlat89 yield criterion theoretical curves with the experimental plastic work contour map,the result shows that the Hill'48 yield criterion is in good conformity with the QP980 material.Fourth,Hill'48 yield criterion is optimized by introducing an equivalent plastic strain parameter.The result shows that average error of optimized Hill'48 theoretical yield trajectory is reduced by 8.4%.Last,finite element model about variable cross-section roll forming is established,then applying the optimized Hill'48 parameter yield criterion to the ABAQUS for finite element simulation.The simulation result shows that the forming quality is good,and in agreement with the actual forming parts.Therefore,the optimized Hill'48 yield criterion can be used to precisely describe QP980 ultra high strength steel.

基于端对端网络模型的手写公式识别

基于encoder-decoder端到端网络结构,提出一种手写公式识别网络模型。与传统方法相比,该模型可以由数据集驱动。利用稠密残差块建立不同感受野增强特征提取,把握全局信息,对手写公式图片进行不同分辨率特征提取,并通过双向循环神经网络的方式捕获图片特征向量上下文关系,有效捕获词向量间的语义关系。该模型对手写图片中的符号分割识别由注意力机制自动执行并优化。利用CROHME提供的标准数学公式手写数据集来验证算法,结果表明该模型具有较好的识别准确率。

建筑外墙保温技术的应用及实施要点之研究

改革开放以来,我国的经济得到了前所未有的发展,建筑行业也取得了一定的发展和进步。目前,建筑行业仍在进行不断的改革,以便满足现代人们的需求。再者,现阶段在绿色施工和可持续发展理念的影响下,人们对建筑外墙保温施工工艺提出了更高的要求,即在建筑设计中不仅更注重建筑外墙的美观,而且更关注建筑物外墙保温技术和保温性能。因此,建筑行业应努力开发建筑墙保温技术,提升建筑外墙保温技术的运用水平和建筑工程的质量水平。

建筑设计中BIM技术的应用

随着我国经济的快速发展,人们的生活水平也在不断提升,促使我国建筑行业的发展速度也越来越快。建筑工程之中最为重要的部分就是设计部分,将会直接影响建筑工程的整体质量。因此,建筑工程设计的质量对于一个建筑行业来说至关重要。BIM技术正是帮助进行建筑工程设计的主要手段,可以为建筑中的设计部分提供相对准确的信息,通过三维建模等功能,为建筑工程设计提供全面的数据。本文主要对BIM技术在建筑工程设计中的应用进行分析。

定模动辊机电系统动力学分析

动力学分析对定模动辊成形装备的设计具有重要意义。论文基于能量原理,针对驱动电动机、传动机构、模具-轧辊系统与成形高强钢板材组成的机电系统,提出一种包含电磁场、机构驱动力场及高强钢板连续塑性变形过程动态能量场耦合机电系统动力学分析新方法。通过推导系统各部分能量数学表达的理论研究,获得定模动辊机电系统动力学方程。采用有限元法获取定模动辊成形过程中的反力矩,以此作为载荷并用Runge-Kutta法求解系统微分方程,揭示了驱动电动机、传动机构、模具-轧辊系统与先进高强钢板材变形组成的系统运动机理,全方位展示装备动特性规律,求得各轴载荷及电动机驱动力矩等系统性能参数,实现先进高强钢变截面定模动辊成形工况匹配设计与精确运动控制。设计的定模动辊成形机与分析结果进行了可行性实验验证。