慢加载时拉伸速率与球墨铸铁的塑性

对于慢加载时拉伸速率对金属材料塑性影响的问题,目前尚无统一的认识.为此,在3.3×100～3.3×10-5s-1范围内连续调整拉伸速率,测定了几种球墨铸铁的力学性能.结果发现,对于通常认为是韧性、介韧性及脆性的球铁,其延伸率均随拉伸速率的减小而呈同一规律改变,即先是逐渐增大,至某一最大值后又逐渐减小,所得曲线呈峰状.正常状态下材料的韧性不同,峰的形状、大小及位置也不同.对于脆性材料,仅在拉伸速率3.3×10-4s-1时呈现出一定的塑性,却也表明在小应变作用下其力学性能的潜力.     

根据拉伸性能预测铝合金板材的疲劳裂纹扩展速率

本文在郑修麟和Hirt提出的疲劳裂纹扩展公式基础上’结合铝合金疲劳裂纹扩展门槛值的经验公式,提出了一个根据拉伸性能预测铝合金板材疲劳裂纹扩展速率的新方法。大量实验数据与估算结果对比表明,本文提出的疲劳裂纹扩展速率估算式是可行、实用的。此外,本文还强调了疲劳裂纹扩展门槛值△K_(th)在疲劳寿命估算中的重要性和工程中的实用性。     

拉伸速率对FGH95缺口小试样断裂性能的影响

研究了不同加载速率和不同的缺口形状对粉末冶金FGH95缺口小试样拉伸断裂性能的影响.结果表明:名义断裂应力σnom随着加载速率的增大而减小;仅对具有相同缺口深度的缺口试样,σnom随着名义应力集中因子Kt的增大而减小,缺口深度对断裂应力的影响远大于缺口形状,当缺口深度达到某一数值,将产生缺口强化现象.随着加载速率的增大,缺口敏感系数Cm呈下降趋势,应力集中因子越大的试样,缺口敏感性越强.γ′沉淀粒子的强化作用和高温动态回复对FGH95高温变形起主要作用.     

超高性能轻质混凝土的循环拉伸力学性能

超高性能轻质混凝土(ultra-high performance lightweight concrete,UHPLC)是一种具有高拉压比和拉伸应变强化特性的轻质水泥基材料.为了阐述UHPLC与钢筋在钢筋屈服点之前的协同受拉机制,针对一种密度为1789 kg/m3、抗压强度为63.1 MPa、极限拉伸应变约为2.4×1...     

渗铸法生产泡沫铝合金的模具设计参数的确定

设计了一套适合制造小孔径泡沫铝合金的渗铸装置，并且生产出了泡沫铝试样。确定了铸型的结构形式和压头与压室间的间隙值，以及铸型所用的涂料，并确定了铸型的最小壁厚。分析了铸型在压渗时存在的应力，指出模具所受切向压力是引起模具破坏的主要力，适当增加壁厚可保证模具在压渗铝合金时不被胀形和弯曲。探讨了食盐粒子的预处理工艺。散状粒子的预处理工艺是将食盐粒子加热至４５０℃，并保温９０￣１２０ｍｉｎ。     

加载速率对缺口前应力、应变分布的影响

用动态有限元法，计算了一种低合金钢在不同加载速率下四点弯曲缺口试样缺口根部应力、应变和应变率的分布．结果表明：缺口前各点的应变率和试样整体屈服载荷Pgy随加载速率的增加而增加；在相同的P／Pgy下，缺口前各点的正应力随加载速率的增加而增加，而应变基本不变．加载速率对缺口前应力、应变分布的影响是由于其引起了缺口前应变率的变化，从而使材料力学性能发生变化所引起的．     

冰的力学性能试验研究

为解决冰凌灾害防治研究中冰的力学参数取值问题,在传统力学试验方法的基础上,通过改进试验设备、控制试验条件,测得了冰体在不同温度(-5、-15、-25、-30、-35、-40℃)及不同加载速率(0.05、0.10、0.30、0.50、0.80 k N/s)下的强度、变形和弹性模量.通过分析,比较不同条件下冰体破坏特征和应力-应变曲线,得出了冰体力学参数及其材料性能,为冰凌灾害防治、冰凌爆破及数值模拟等研究提供了数据参考.     

紧凑拉伸试样加载孔对裂纹的干涉作用

通过增量理论弹塑性有限元计算,对比分析了带和不带加载孔ＣＴ试样Ｊ积分之间的差异,提出裂纹长度与试样宽度之比大于等于０．６时,可完全忽略加载对Ｊ积分的干涉作用,另餐,采用ＣＴ试样讨论失效评定曲线时也应考虑加载孔的干涉作用。     

加载速率对CA砂浆抗压强度的影响

CA砂浆中沥青的大量存在使得其力学性能具有较强的时间依赖性.首先研究了CA砂浆抗压强度在不同加载速率下的变化规律及沥青乳液与水泥的相对质量比、砂的细度模数与外掺料硅灰(SF)和橡胶粉(CR)对CA砂浆抗压强度时间依赖性的影响.结果表明:CA砂浆的抗压强度随加载速率的升高呈增加趋势,沥青的相对含量越低,增加趋势越明显;砂的细度模数越小,CA砂浆的抗压强度对加载速率的稳定性越好,但同时会导致CA砂浆的流动性损失过大.SF和CR对CA砂浆表现出的时间依赖性有不同程度的改善作用.同时提出了沥青在CA砂浆中的理想分布模型,对其力学性能的时间依赖性进行了解释.     

双辊铸轧超高强铝合金有限元数值模拟

采用有限元法对双辊铸轧7075和7050铝合金的工艺过程进行了数值模拟,研究了合金成分和铸轧速度对铸轧熔池内温度场、流场和凝固场的影响规律。结果表明,在同一铸轧速度条件下,随着合金的等效比热增大,合金在铸轧熔池内的温度梯度随之减小,凝固速率减慢;对于同一种合金,随着铸轧速度增加,合金的速度梯度随之增大,熔池内所形成漩涡的位置下降。模拟结果为下一步的铸轧实验提供了理论依据     

挤压铸造ZA27合金的力学性能及摩擦磨损性能

研究了挤压铸造对ZA27合金力学性能的影响,挤压铸造可以显著地提高ZA27合金的常温力学性能和高温力学性能.随着比压的增加,其综合力学性能提高.比压为750 MPa时,与金属型重力铸造合金相比,抗拉强度提高了约19.2%,硬度提高了约25.5%,伸长率增加了12.3%.采用MM-W1立式万能摩擦磨损试验机研究了比压对ZA27合金的摩擦磨损性能的影响,结果表明,在转速为200 r/min,载荷为100 N,摩擦副为45钢,20号机油润滑条件下,挤压比压为750 MPa时,合金的摩擦磨损性能较好.     

低频电磁铸造铝合金结晶器材料优化设计

低频电磁场作用下铸造铝合金过程中结晶器设计的好坏对保证铸坯质量起到很重要的作用,而在结晶器设计时数值模拟技术是一个重要有效的工具.优化的结晶器应该是在电源频率相同较低的电流下在铝熔体内部能够获得所需要的磁场强度.基于这种思想,根据生产实际情况,设计出工业上实用的低频电磁铸造铝合金结晶器.在结晶器外套材料不同情况下,对低频电磁铸造铝合金过程的电磁场进行了三维有限元数值模拟.模拟结果表明,当结晶器外套为软磁材料时,铝熔体内部磁场强度得到明显加强.     

Squeeze casting of Al-Cu alloy

In order to use the cast method to replace forge method in producing the load-bearing wheel used in certain heavy duty vehicle, simplified and reduced size load-bearing wheels were squeeze cast and studied using Al-Cu alloy. Tensile properties, hardness, microstructures and morphologies of the squeeze-cast wheels were investigated. The results show that the finer microstructure, higher density, strength, toughness and hardness were achieved through the squeeze casting. Ultimate tensile strength of 428 MPa, yield strength of 360 MPa, elongation of 13.1% were achieved for T5 heat-treated squeeze-cast wheels. The Brinell hardness of squeeze-cast wheels is from HB 120 to HB 137.     

挤压铸造对ZA27合金组织及性能的影响

研究了挤压铸造对ZA27合金组织及性能的影响.挤压铸造可以显著提高合金的综合力学性能，抗拉强度指标提高了约19.2%，硬度指标提高了约25.5%，延伸率比重力铸造合金增加了近2倍.挤压铸造使合金的组织细化，并使组织中共晶体的数量明显增多，尺寸减小.共晶体由粗大的长条状变成细小的层片状，ε相由棒状或块状变成细小的点状弥散分布于枝晶间.电子探针分析表明，挤压铸造明显改善了合金元素的显微偏析，使试件整体成份均匀.     

直接冷却半连续铸造铝合金圆锭水冷边界试验研究

通过试验方法测定直接冷却半连续铸造铝合金圆锭凝固过程的温度变化曲线,利用逆向法计算出铸锭表面换热系数,并进行理论分析.研究表明,水冷换热系数与铸锭表面温度的关系曲线可作为直接冷却半连续铸造过程数值模拟的水冷边界条件.     

Rheological behavior of continuous roll casting process of aluminum alloy

The rheological behavior of aluminum alloy and its influencing factors in physical simulation of continuous roll casting process were studied by using a Gleeble-1500 thermal-mechanical simulation tester with a set of special clamp system. The relationships between the flow stress and the strain rate in the deformation process of simulating roll casting experiment were obtained. The results show that four different characteristic stages exist in the temperature range of the whole rheological process. The first occurs when the temperature is higher than 600℃, which belongs to the creep deformation stage; the second occurs when the temperature lies in the range of 500 - 600℃, and it can be regarded as the high temperature and low stress level deformation stage; the third occurs when the temperature decreases to the range of 300 - 500℃, it is considered to be the middle stress level deformation stage; the last occurs when the temperature is less than 300℃ and the strain rate is less than 1.00 s^-1 , it belongs to middle stress level deformation stage. But when the strain rate is larger than 1.00 s^-1, it belongs to the high stress level deformation stage. And the relative constitutive models suitable for the four different stages of continuous roll casting process were established through multivariate linear regression analysis of the experimental data.     

Effect of ultrasonic power and casting speed on solidification structure of 7050 aluminum alloy ingot in ultrasonic field

With the experiment and finite element simulation, the influences of power ultrasonic on the solidification structure of 7050 aluminum alloy ingot in semi-continuous casting were researched, and the effects of casting speed on solidification structure in ultrasonic field were also analyzed. The experiment and simulation results show that the solidification structure of the ingot is homogeneously distributed, and its grain size is obviously refined at ultrasonic power of 240 W. The average grain sizes, which can be seen from the Leica microscope, are less than 100 μm. When the casting speed is 45-50 mm/min, the best grain refinement is obtained.     

Mechanical properties of directionally solidified lead-antimony alloys

The Pb-17wt％ Sb alloy was directionally solidified under two solidification conditions:with different temperature gradients (G=0.93-3.67 K/mm)at a constant growth rate(V=17.50 μm/s)and with different growth rates(V=8.3-497 μm/s)at a constant temperature gradient(G=3.67 K/mm)in a Bridgman furnace.Microstructure parameters,such as primary dendrite arm spacing(λ1),secondary dendrite arm spacing(λ2),and dendrite tip radius(R),were measured.The microhardness(Hv)and ultimate tensile strength(σ)of the directional solidification samples were also measured.The influences of solidification and microstructure parameters on Hv and σrwere investigated.The results obtained in this work were compared with similar experimental researches in literatures.It is shown that the Hv and σrvalues increase with the increase of G and V,but decrease with the increase of λ1,λ2,and R.