船用钢Q345D中温塑性成形本构方程建立及分析

采用SANS-CMT万能材料试验机,在温度为473~973K和变形速率为0.001~0.1s~(-1)范围内对Q345D钢板试样进行拉伸实验,并对应力应变实验数据进行分析。结果表明:温度对Q345D钢中温塑性成形影响较大,而应变速率对成形影响较小。随着温度的升高,材料屈服强度σ_s和抗拉强度σ_b出现直线下降,较低温度下,拉伸应力应变曲线出现明显的屈服平台;塑性变形过程中存在着明显的加工硬化现象,加工硬化指数n随温度的上升而下降;延伸率δ随温度的升高近似线性增长;应变速率敏感系数m随温度的升高线性下降。     

轨道横向动力特性振型叠加法分析

本文对包括两根钢轨、轨枕、道床的点支承欧拉梁轨道横向振动力学模型,用振型叠 加法进行了分析,得到了20一500比频率范围内的位移响应.它与轨道实际情况有良 好的一致性。计算结果表明,本方法分析频率范围广,计算量小,是分析软道横向动力 特性的有效方法。      

钢-铝石墨半固态铸轧复合的数值模拟

铸轧区的温度分布直接影响着铸轧过程的稳定性和复合板材的质量.针对实验室复合板半固态铸轧试验的特点建立了数学模型,采用有限元法对钢-铝石墨半固态铸轧复合过程的热流耦合问题进行了数值模拟计算,分析了不同浇注温度和铸轧速度下熔池内温度场变化的情况.模拟结果表明,当浇注温度为620℃,铸轧速度在0.6～0.8 m/min的范围内可保证铸轧稳定进行,此结论与试验数据相吻合.该模型可以有效预测凝固前沿位置,为半固态铸轧复合工艺的进一步研究和钢-铝石墨复合板的数字化生产提供了依据.     

二维薄板在超音速气流作用下的热弹性颤振

根据von-Karman几何非线性应变位移关系建立了二维薄板在超音速气流作用下的非线性动力学模型,其中气动力根据一阶准静态活塞理论计算.用假设模态法和伽辽金方法使方程离散化,然后用Runge-Kutta方法计算.分析结果用分叉图和相图描述.结果表明,温度效应降低了板的稳定性;随动压增大,系统经历稳定运动、周期运动和混沌运动状态.     

13CrMo44钢及焊缝金属的疲劳裂纹扩展速率

本文根据美国ASTM F647-81标准,采用紧凑拉伸试样,对13CrMo44钢及用P5(E309Mo)焊条的手弧对接焊缝金属的疲劳裂纹扩展速率进行了测定.试验采用表面直读法测量裂纹长度、并采用抛物线回归法对大量试验数据进行微机处理.基于Paris公式,得到了13CrMo44钢和焊缝金属的裂纹扩展速率的表达式.     

强度等级对混凝土动态抗压特性的影响分析

混凝土的动态与静态力学特性有很大的不同.为了明确混凝土在动态荷载作用下的抗压特性,以及强度等级对其动态抗压特性的影响,通过试验得出各等级混凝土在高应变速率下的力学性能相较于静态时力学性能的变化,为建立动态作用下的混凝土力学本构关系打下基础.     

改良废旧轮胎混合材料动力特性试验研究

为深入研究冻融循环条件下废旧轮胎颗粒材料的改良方法及动力特性,通过室内试验,确定了废旧轮胎颗粒材料的改良配比.利用改良后的废旧轮胎混合材料制备了若干试样进行动三轴试验,获得了不同温度、冻融循环次数和循环加载次数下试样的动应力-动应变关系曲线.试验结果表明:在动应变5％以内,混合材料试样的动应力-动应变关系曲线无明显峰值点,具有显著的应变强硬化特征;在-15～20℃范围内,试样的破坏强度随温度降低而增加,随冻融循环次数和循环加载次数增加而降低,而且两者对常温试样破坏强度影响较小,对冻结试样影响较大.     

5A06铝合金板材热态本构模型及韧性断裂准则

为了获取材料在不同条件下成形性能指标,对5A06铝合金板材进行了热态单向拉伸试验,结合热态单向拉伸试验和韧性断裂试验结果,提出了一种修正Misiolek模型;利用修正模型的外插性能预测颈缩后板材流变应力,应用径向基函数神经网络算法建立了Cockroft-Latham韧性断裂阈值预测模型,并对该模型进行了预测精度评估.结果表明,流变应力对温度及应变速率敏感,对比径向基函数网络模型预测误差小于10.6%.      

基于桁梁实桥试验的钢管混凝土界面传力机制

为分析钢管混凝土桁梁桥的承载性能和钢-混凝土组合作用机理,进行了桁梁上、下弦钢管混凝土界面传力行为实桥试验和全桥板壳-实体有限元参数分析;以主跨71 m的简支半穿式钢桁梁桥为依托,沿其上、下弦杆节间长度范围内共布设102个应变测点,测试并分析了加载车作用下钢管轴向应变分布和钢-混凝土界面传力特征;采用ABAQUS软件建立了试验桥板壳-实体有限元模型,经实测挠度与应变数据验证模型的可靠性后,进行了界面连接状态、界面抗剪刚度、钢管厚度、管内混凝土强度等对钢管混凝土界面传力性能的参数影响分析。分析结果表明:钢管轴向应变分布规律可反映钢管混凝土界面传力的基本特征;钢管混凝土桁架上、下弦杆节点区域均出现界面剪力不均匀分布现象,钢-混凝土界面有效传力范围内钢管轴向应变呈负指数函数分布,其他区域钢管轴向应变保持不变;完全脱黏的钢管混凝土桁架弦杆的钢管轴向应变在节点一定范围内呈二次抛物线函数分布;钢管轴向应变因界面连接状态所表现出的不同应变分布规律和剪力传递长度可用于评价钢管混凝土组合作用强弱和界面工作状态;桁架弦杆的剪力传递长度随钢管厚度和管内混凝土强度的增加而增大,钢管厚度的影响更显著;在钢管混凝土桁架弦杆内设置抗剪连接件可缩短剪力传递长度。      

纵向冲击下高速列车车体承载极限数值模拟

进行了高速列车车体6005A-T6、6082A-T6铝合金的静态拉伸和动态压缩试验，识别了0.001~2 500 s-1应变率范围内2种铝合金的材料应变率效应，建立了对应的Johnson-Cook本构模型；构建了高速列车典型车辆的显式动力分析模型，完成了刚性墙冲击车体过程仿真，研究了车钩稳态载荷、冲击速度、加载方式对车体承载极限的影响；分析了高速列车一号车和二号车车体在冲击载荷下的变形演化，通过应力变化临界点确定了车体的承载极限，并对列车在更高能量配置模式下的车体承载性能进行了验证。研究结果表明:在0.001~2 500 s-1应变率范围内，6005A-T6和6082A-T6铝合金应变率敏感系数分别为2.9×10-3和8.5×10-3，应变率效应不明显；纵向动态冲击载荷下，应变率强化对铝合金车体结构承载力影响不明显，惯性效应是其承载能力高于静态极限的主要原因；纵向冲击载荷从车钩位置传递时，一号车和二号车车体的动态承载力水平显著高于车体许用静态压缩载荷；冲击载荷下的车体结构承载力可为高速列车碰撞各界面能量分布问题中吸能元件平台力取值提供上界；可适当考虑提高车体许用压缩载荷以扩大列车端部吸能部件力学参数设计域，以满足更苛刻需求下的列车被动安全性能。      

Static softening characteristics and static recrystallization kinetics of aluminum alloy A6082 after hot deformation

The static softening behavior of aluminum alloy A6082 was investigated by interrupted hot tests conducted on Gleeble-1500 simulator at deformation temperatures from 573 to 773 K and strain rates from 0.1 to 10 s⁻¹, with a pre-strain from 0.3 to 0.7 and variable inter-pass delay times. The offset method was applied to convert the changes in flow stress between two passes to static softening fraction. The microstructural changes were characterized by the quantitative metallography of quenched specimens. The results showed both static softening and static recrystallization curves exhibited a simple sigmoidal shape; the static softening is related to the static recrystallization in a nonlinear manner with 50% static recrystallized volume fraction corresponding to 80% static softening fraction; an increase in temperature, strain rate or pre-strain yields a decrease in the time for 50% static recrysallized volume fraction, on which the temperature has the most remarkable influence; Si and Mn additions accelerate the process of static recrystallization. Finally, the equations of static recrystallization kinetics of this alloy were developed with a good agreement between the predicted and experimental results.     

在室温及低温下316L、316LN不锈钢单轴低周疲劳特性的研究

本文在室温及低温下对316L、316LN奥氏体不锈钢进行了单独拉压低周疲劳试验及其微结构观察，利用穆斯堡尔谱方法，间接地证实了至今尚未得到试验证实的在316LN不锈钢中存在IS结合体的假设，基于宏观微观试验研究结果，深入研究了不锈钢的单轴低周疲劳特性对合金元素氮和试验温度依赖性的微观机理。     

Effects of cooling rates on microstructures and mechanical properties of Nb-Ti microalloyed steel

The mechanical properties and microstructure of as-cast Nb-Ti microalloyed steel at different temperatures and cooling rates are investigated in this paper. The III brittle zone (700?C900°C) is revealed. The reduction of the hot ductility is due to the film-like proeutectoid ferrite or the Nb(C, N) precipitates along the austenitic grain boundaries. In the temperature range of 850?C1 000°C, with the increase of the cooling rate, the hot ductility decreases. However, in the range of 650?C850°C, the appearance of large volume fractions of ferrite on austenite grain boundaries minimizes the effect of cooling rate on hot ductility. When the cooling rate is 10°C/s, austenite transforms more quickly to ferrite and at a lower temperature a larger amount of ferrite nucleates and precipitates in the grain, which leads to a sharper improvement in the hot ductility at 650°C.     

Dynamic recrystallization behavior and microstructural evolution in SPHC steel

The dynamic recrystallization(DRX) behaviors in SPHC steel were investigated with hot compression tests at deformation temperatures of 950-1 150,strain rates of 0.1-15 s-1,and initial austenite grain sizes of 86-232 μm.The effects of deformation temperature,strain,strain rate and the initial austenite grain size on the microstructural evolution during DRX were studied in detail.The results show that DRX is observed under the condition of the Zener-Hollomon parameter being less than 1.07×10 13 s-1.The deformation activation energy for SPHC steel is calculated to be 299.4 kJ/mol by regression analysis.Austenite grain size of DRX is refined with decreasing temperature and increasing strain rate under steady state conditions,but it is not influenced by the initial grain size.The mathematical equation of DRX grain size of SPHC steel is obtained.     

Influence of soaking temperature on microstructure of multi-pass compression deformation for low carbon steels

The influence of soaking temperature on microstructure of high temperature multi-pass compression deformation for two low carbon steels (steel A: w _C = 0.032% and w _Mn = 0.25%; steel B: w _C = 0.165% and w _Mn = 0.38%) is studied on the thermal-mechanical simulator in order to rationalize the hot-rolling schedule of low-carbon steel and to promote the low-temperature heating technology. The results show that the microstructures of steel A are almost not affected by reducing soaking temperature, but the acicular ferrite forms in steel B when the soaking temperature is reduced from 1 200 to 1 170°C, due to its smaller initial austenite grain size according to recrystallization kinetics theory.     

氮对奥氏体不锈钢氢脆敏感性的影响

本文研究了气相充氢条件下,氮对２１—６—９奥氏体不锈钢力学性能的影响,以及不同牌号的Ｃｒ─Ｎｉ—Ｍｎ系奥氏体不锈钢充氢后力学性能的变化。结果表明,不同牌号奥氏体不锈钢的抗氢脆能力随其层错能的增加而提高,氮含量的增加则使２１—６—９钢的抗氢脆能力下降。由此推论氮可能具有降低奥氏体钢层错能的作用。     

北京地区不同类型土壤的吸附和降解性能

在静态条件下,研究了北京地区4种不同类型土壤对氨氮和有机物的吸附和降解效果,在室内进行了15℃和24℃情况下的静态吸附实验,以及室内静态降解实验．实验结果表明：氨氮在不同类型土壤中的吸附过程基本符合线性模式,有机物在不同类型土壤中的吸附过程基本符合指数模式,黏土和重粉质黏土试样对氨氮和有机物的吸附规律都是随着温度升高吸附量反而下降,氨氮和有机物在不同类型土壤中的降解过程符合一级动力学方程模式．     

Microstructure Evolution of Different Forging Processes for 12％Cr Steel During Hot Deformation

Five forging experiments were designed and conducted to investigate the effect of process parameters on microstructure evolution during hot deformation for X12CrMoWVNbN10-1-1 steel.The experimental results indicated that average grain size became finer with the increasing number of upsetting and stretching.Especially,the size of stretching three times with upsetting twice had the most remarkable effect on refinement,and the size was only 27.36%of the original one.Moreover,the stress model was integrated into the software and finite element models were established.Simulation results demonstrated that the strain at center point of workpiece was far larger than critical strain value in each process,so that dynamic recrystallization(DRX) occurred in each workpiece,which implied DRX could occur for several times with the increasing number of upsetting and stretching,and uniform finer microstructure would be obtained.However,the results also showed that higher temperature was an unfavorable factor for grain refinement,so the times of heating should be limited for workpiece,and as many forging processes as possible should be finished in once heating.     

Investigation on Zener-Hollomon Parameter in the Warm-Hot Deformation Behavior of CF53

The warm-hot deformation behavior of CF53 steel was studied with hot compression tests at temperature of 1 123 ~1 273 K and strain rate of 0.1~20 s -1 . The activation energy for warm-hot deformation is 274.816 kJ/mol. The influences of Zener-Hollomon parameter, strain and grain size imposing on the flow stress were analyzed in the temperature range of warm-hot forging. Based on the creep theory and mathematic theory of statistics, mathematical models of flow stress were obtained. The results provide a scientific basis for controlling microstructure of forging process through Zener-Hollomon parameter.