几个强度理论的屈服实验研究

根据多种塑性金属的二向和三向拉伸与压缩组合主应力屈服强度实验数据,对Tresca强度理论、Mises强度理论、Mohr-Coulomb强度准则、Beltrami最大能量理论、极限应变能强度理论等几个强度理论计算的相对误差进行了比较分析。结果表明极限应变能强度理论计算的误差在10%以内,为最小。Tresca强度理论、Mises强度理论和Mohr-Coulomb强度准则计算的误差分别为-36%、-27%、-23%,计算结果比试验结果偏保守。Tresca强度理论和Mises强度理论都不适用于拉伸屈服强度和压缩屈服强度相等的材料,该材料的理论剪切屈服强度为拉伸屈服强度的倍。极限应变能强度理论可用于二向和三向拉伸与压缩组合主应力强度计算,在全拉伸和全压缩主应力状态下与Rankine强度理论一致,具有工程应用前景和价值。     

模拟点腐蚀油气管线钢的力学性能

通过计算机产生随机数确定点腐蚀孔的位置,利用小钻头打孔的方法模拟X60管线钢基体多孔特征进行拉伸试验,测得其弹性模量、屈服强度和抗拉强度,并将理论计算值与前二者比较,给出了三者与孔隙率的函数关系.结果表明,多孔材料的弹性模量试验值随其孔隙率的变化在低孔隙率时与理论预测基本吻合;实测材料的屈服强度也随着孔隙率的增加而递减,与理论预测也基本吻合,特别是较高孔隙率时相近或相同;实测材料的抗拉强度随孔隙率的变化拟合曲线与屈服强度相似,但受孔隙率影响较大.     

沉淀强化镍基合金屈服强度的理论计算EI

本文提供了依据合金的化学成分、显微组织参数定量计算合金屈服强度性能的理论方法。具体计算了一组镍基合金的室温屈服强度，计算值与实测值很好地符合。     

金属FCC-Al热容的研究

用OA理论结合Debye-Grüneisen模型,计算了FCc-Al从0K到熔点(933.47K)的热容曲线.将计算结果与实验值进行比较,发现理论值偏低,对其原因进行了系统分析.对理论模型计算值进行适当修正,发现修正后的数据和实验值较吻合.与SGTE数据库绘制的热容曲线比较,得知SGTE给出的FCGAl的热容数据不完善.最终由理论计算的修正值并结合SGTE数据库,给出了从0K到沸点FCC-Al的热容曲线,实现了对金属元素Al热容的完整描述.     

钢筋砼梁与柱的抗剪强度理论解

本文采用协调桁架模型与钢筋砼受剪单元的修改受压屈服理论，推导了钢筋砼梁、框架柱的抗剪强度理论计算式，该式由三部分组成，即箍筋的抗剪、剪压区砼的抗剪和砼拉应力作用的抗剪。计算式与５７个试件的实测值对比，表明具有较高精度。     

钨合金细观参数对其宏观屈服强度的影响

通过细观分析,给出钨颗粒相的形状、组分和两相力学参数对钨合金宏观屈服强度的影响.其中,钨颗粒看作基体上的夹杂,在小变形条件下假设钨颗粒仅发生弹性变形,而钨合金的宏观屈服强度决定于基体相的屈服强度.在该假设基础上,利用Eshelby方法及Mori-Tanake平均应力概念计算分析了不同钨合金材料,特别是不同变形量工艺处理的钨合金材料的宏观屈服强度,计算结果与实验结果基本一致.     

油气输送管典型应力状态下的屈服行为研究

准确计算油气输送管的实际屈服强度对合理确定输送压力有重要影响。该文分析了4种应力状态下对屈服强度有明显影响的钢管轴向应力,发现管材横向小试样试验时,轴向应力为零,工厂静水压试验时,轴向应力小于零,裸露钢管静水压试验时,轴向应力为环向应力的一半,埋地服役状态时,轴向应力为0.3倍环向应力。并从理论和试验两方面分析了实物钢管屈服强度与管材小试样屈服强度的差别。理论计算表明,4种应力状态下,屈服时vonMises理论计算的钢管环向应力值大于或等于Tresca理论计算值,其中裸露钢管受内压状态下,vonMises理论计算的管道屈服环向应力为1.15倍管材屈服强度,Tresca理论计算值为1.0倍,6根钢管爆破试验及小试样拉伸试验表明,该值为1.18倍。vonMises理论比Tresca理论更适合油气输送管的屈服计算。     

基于双剪统一屈服准则的混凝土矩形板极限荷载的研究

采用双剪统一强度理论（俞茂宏,1991）求出了矩形板的塑性极限荷载的统一解,得出了不同参数b值对极限荷载的影响曲线,从而得出了一系列从Tresca的单剪屈服准则解到双剪应力屈服准则（俞茂宏,1961）的矩形板极限荷载。文献中己有的Tresca解为本文的一个特例。将其用于混凝土矩形板的极限荷载计算,得出了满意的结果。双剪统一强度理论可以给出更符合于各种不同材料特性的合理解。     

强度理论的发展和展望

强度是各种地上、地下、水下和上天结构的共同的最基本要求。强度理论是研究材料在复杂应力下屈服和破坏规律的学科。由于各种土木、水利、机械、航空、军工等工程结构中的材料,大多处于复杂应力作用下,因此强度理论得到广泛的研究和应用。强度理论是各种工程结构强度计算和设计必需的基础理论。它们也是固体力学、材料强度学研究从弹性到塑性,从弹性到软化或硬化,从弹性到脆塑性,以及从线性到非线性的开始。对材料在复杂应力状态下强度理论(屈服准则、破坏准则等)的发展进行了总结。给出了 80 多种准则的方程式,反映出强度理论研究的“百花齐放,百家争鸣”。讨论了各种准则的分类和它们之间的关系,以及在研究和工程应用中的合理选择破坏准则问题。还总结了三大系列强度理论、统一屈服准则、统一强度理论和其他各种强度理论。 最后讨论了强度理论的发展展望,包括:真三轴试验和假三轴试验;强度理论的经济效益;各向异性材料和复合材料的破坏准则;多孔隙材料和多相材料的破坏准则;其它各种特殊材料的强度理论;安定性、多轴疲劳、蠕变、损伤、断裂和相关现象;强度理论的计算机程序实施和角点奇异性;特殊环境下的强度理论问题;强度理论的美;强度理论研究的不同层次。 在连续介质和工程应用的框架下     

收发分置式声纳系统混响仿真方法

给出了收发分置式声纳系统混响的一种仿真方法,首先推导出收发分置式声纳系统的体积混响、海面混响、海底混响的等效平面波混响级公式,并由等效平面波混响级公式计算出平均声强度衰减规律,与由声线法计算平均声强度衰减规律相比,仿真实现时计算更简单。并对仿真结果进行了平均混响强度衰减规律分析和统计特性与时间相关特性检验,与理论值相比较具有一致性,为收发分置式声纳系统的目标检测、信息传输技术研究提供理论依据。     

基于液氦温区测试高真空多层绝热性能的量热器设计

设计了一个用于测试液氦温区的多层绝热材料的量热器平台,对量热器进行了结构设计、力学分析和理论漏热计算以验证平台可靠性。力学分析的结果表明,量热器最大的位移变形量为0.16 mm,位于下保护胆底部封头;应力最大为49 MPa,位于液氮冷屏的顶部封头处。理论漏热计算的结果表明,当稳定测试时间为8 h时,所设计的容器容量均满足需求。基于力学分析和理论漏热计算的结果,得知所设计的量热器满足测试多层绝热性能的要求。     

Thermophysical Properties of Automotive Metallic Brake Disk Materials

The temperature distribution, the thermal deformation, and the thermal stress of automotive brake disks have quite close relations with car safety; therefore, much research in this field has been performed. However, successful and satisfactory results have not been obtained because the temperature-dependent thermophysical properties of brake disk materials are not sufficiently known. In this study, the thermophysical properties (thermal diffusivity, the specific heat, and the coefficient of thermal expansion) of three kinds of iron alloy series brake disk materials, FC250, FC170, and FCD50, and two kinds of aluminum alloy series brake disk materials, Al MMC and A356, were measured in the temperature range from room temperature to 500 °C, and the thermal conductivity was calculated using the measured thermal diffusivity, specific heat capacity, and density. As expected, the results show that the two series have significant differences in respect of the thermophysical properties, and to reduce the thermal deformation of the brake disk, the aluminum alloys with a high thermal conductivity and the iron alloys with low thermal expansion are recommended.     

高温合金热处理工艺研究进展

高温合金是一类在高温及一定应力条件下长期工作的高温金属材料,具有良好的综合性能,被广泛地应用于航空航天等领域。适当的热处理工艺通过改变合金的微观组织来提升其性能。总结了近几年高温合金热处理工艺的研究进展,详细论述了变形高温合金、铸造高温合金和粉末高温合金的热处理工艺及热处理对其组织和性能的影响,并阐述了高温合金热处理工艺的发展趋势。     

强动载荷下焊接钢板力学性能及本构模型研究

为研究强动载荷下船用焊接钢板的力学性能。开展了典型船用焊接钢板母材、焊缝和热影响区的准静态拉伸试验、高温拉伸试验及SHPB动态压缩试验,分析了焊接钢板材料在不同应力状态下的力学行为,基于力学性能试验结果拟合了焊接钢板母材、焊缝和热影响区材料的本构模型。结果表明:准静态条件下,与母材相比,焊缝和热影响区材料的屈服强度与抗拉强度偏大,延伸率偏小;高应变率下,热影响区材料抵抗塑性变形的能力明显强于其他两种材料,且随着应变率的增加抵抗塑性变形的能力呈增强趋势;焊接板母材、焊缝与热影响区材料均表现出应变率效应和温度效应;热影响区是焊接板抗冲击性能相对薄弱的区域。建立的Johnson-Cook模型可以描述强动载荷下焊接钢板的力学性能。     

5083铝合金热压缩流变应力曲线修正与本构方程

在Gleeble-3800热模拟机上采用等温压缩实验研究5083铝合金在变形温度为523~723K、应变速率为0.01~10s-1、真应变为0~0.7条件下的高温流变应力行为。基于热传导对合金变形热效应的影响,对流变应力曲线进行了变形热修正。结果表明:热传导对变形过程中产生的温升影响不可忽略,其影响随着真应变的增加而更加显著;修正后的流变应力对峰值应力影响不大,但稳态流变应力软化趋势得到一定程度的减弱。建立了Zener-Hollomon参数的本构方程,可对5083铝合金在不同变形条件下的流变应力进行预测,温升修正后的流变应力值与本构方程的预测值吻合较好,平均相对误差仅为5.21%。     

Theoretical assessment of influence of deformation induced heating on mechanical behaviour at elevated temperatures

Abstract

When a material is deformed, most of the work done by the applied stress is dissipated as heat. For low rates of deformation or for small blocks of material, the loss of heat to the surroundings is rapid relative to the rate of heat generation and the temperature rise is therefore minimal. Under the opposite conditions however, a significant temperature profile can develop within the material. For thermally activated deformation at elevated temperatures, this can have a significant effect on the mechanical response. This is investigated theoretically in the present work. It is evident that the creep of materials in the presence of a temperature profile is central to the understanding and an analysis of this forms the first part of the paper, where creep under uniaxial stress, in bending and in torsion are treated. In the next section, deformation heating under adiabatic conditions is considered and finally, numerical analyses are given for cases where deformation heating occurs with concurrent conduction to the surroundings. Some examples where deformation self-heating is likely to be important are discussed. These include superplastic behaviour, thermal fatigue, rapid stress rupture tests, depressurisation of nuclear reactors, and the deformation of planetary material.     

Effect of low temperature on plastic deformation in structural materials in a complex state of stress

The results of experimental studies of elastoplastic deformation in structural materials of different grades in a complex state of stress at low temperatures are analyzed. It is shown that the degree of the effect of temperature and force conditions on the character of materials’ strain hardening at low temperature depends on their nature and structural state. The principal hypotheses and postulates that form the basis of the modern plasticity theories are examined for low temperatures. Two new models are introduced to describe the elastoplastic deformation of quasi-brittle and metastable materials under the simple loading with consideration for the effect of low temperatures on their structural state and mechanical properties.     

Application of digital-image-correlation techniques in analysing cracked cylindrical pipes

Cracks induced by external excitation on a material that has defects may generate the stress concentration phenomenon. The stress concentration behaviour causes local buckling, which will induce the damage of the members made of this material. Thus, developing techniques to monitor the strain variation of a cracked member is an important study. The traditional technique (such as strain gauge) can only measure the average strain of a region. The strain variation within this region cannot be determined. Therefore, it cannot sufficiently reflect the mechanical behaviour surrounding the crack. The Digital image correlation technique recently developed is an image identification technique to be applied for measuring the object deformation. This technique is capable of correlating the digital images of an object before and after deformation and further determining the displacement and strain field of an object based on the corresponding position on the image. In this work, this technique is applied to analyse the mechanics of a cylindrical pipe experiencing crack destruction. The fixing device is used to avoid shaking the specimen during the pressurizing process. The image capture instruments are fixed on the stable frame to measure the deformation of specimen accurately. Through the cylindrical pipe cracking test, the capacity of the digital image correlation technique for surveying the strain variation in a tiny region is validated. Then, the experimental results obtained using the digital image correlation analysis is used to demonstrate the crack development tendency in defect materials and the stress concentration zone.     

含孔洞聚合物材料破坏过程中的热量生成

对含孔洞聚合物材料表面应力拉伸失效过程中由于不可逆变形引起的热量生成进行了实验研究，利用上测温技术观测，记录和初步分析了孔洞局域温度场的形成和演变规律，研究表明，聚合物材料的损伤与断裂过程是热力耦合的，在我们的具体实验中，材料宏观破坏时的生成热约为外力功的４４％，可见，它对材料失效的影响是不可忽略的，同时，结合形变的微观和细观物理机制，对实验中观测到的变浊规律作了初步的定性解释。     

Study on plastic deformation behavior of hot splitting spinning of TA15 titanium alloy

The plastic deformation behavior of hot splitting spinning of TA15 titanium alloy is a complex metal forming problem with multi-factor coupling interactive effects. In this paper, on condition of considering various thermal effects, a three-dimensional (3D) elastic–plastic coupled thermo-mechanical finite element (FE) model of hot splitting spinning of TA15 titanium alloy is established using the dynamic, temp-disp, explicit module of FE software ABAQUS. Based on the analysis of flow behaviors of TA15 titanium alloy, the mechanism and influence of materials plastic deformation behavior during the forming process are studied. The results show that, the flow stress of TA15 titanium alloy generally decreases with the increase of deformation temperature; at the same strain rate, the higher temperature is, the lower flow stress is. The temperature distributions along the circumferential direction of disk blank are even and the temperature of plastic deformation area is about 984 °C. The heat from plastic deformation and friction at local plastic deformation area is less than the dissipated heat, so the temperature just falls into approximately 945 °C. Radial spinning force as the driving force of plastic deformation increases gradually and reaches about 35 kN at the end. The maximum value of equivalent stress is presented in fillet part between disk blank and two mandrels. The distributions of equivalent plastic strain appear the large strain gradients and the obvious characteristics of inhomogeneous deformation. When friction factor on interfaces between disk blank and dies ranges from 0.4 to 0.6, the forming quality and precision are highest.