TiB2基陶瓷/42CrMo合金层状梯度材料力学测试与结构设计

在以往超重力场合成梯度材料的基础上，制备出组分含量TiB₂-TiC-Fe呈连续梯度变化的TiB₂基陶瓷/42CrMo合金梯度材料. 对材料进行XRD，SEM，硬度测试以及三点弯曲强度测试，并采用电测法获取陶瓷基体部分的弹性模量，并在此基础上，对中间过渡区的弹性模量进行拟合，最后再采用解析方法计算梯度材料的应力应变分布. 结果表明，TiB₂基陶瓷/42CrMo合金相界呈连续梯度变化，硬度自陶瓷顶部至合金底部呈梯度递减.三点弯曲测试发现TiB₂基陶瓷/42CrMo合金材料具有类似于金属的塑性变形特征，从而出现明显的失效延迟行为. 采用电测法得出纯陶瓷组分的弹性模量约为560 GPa，参数拟合得出中间过渡区的弹性模量变化形式更趋近于三角函数，计算得出的应力表示自金属底部出现损伤，而后裂纹向陶瓷顶部方向扩展，与该材料试验现象契合.     

陶瓷材料的力学性能评价新方法

论述了结构陶瓷材料的非破坏性测试和力学性能评价新技术的系列新技术。包括材料表面局部强度的非破坏性测试，位移敏感压痕技术和痕迹预测。这些新方法可以对服役中的陶瓷材料和部件进行在线测试和可靠性预测，为脆性陶瓷的工程应用和安全检测提供了一种简易的评价手段。     

影响拉伸试验性能数据的主要因素

单向拉伸试验是应用最广的一种力学性能试验,试验可以得到材料最主要的一系列性能数据,如弹性模量、泊松比、屈服强度、抗拉强度、伸长率与断面收缩率等.这些数据是控制生产过程中材料质量,评价新材料和机械设计的主要依据.因此,保证实验数据测定准确十分重要.     

挠度修正法评价碳/碳复合材料的高温弹性模量

作为理想的高温结构材料,碳/碳(C/C)复合材料的高温弹性模量对其高温热应力分析及结构设计至关重要。三点弯曲试验可以采用电感量仪准确测得陶瓷试样的挠度,从而计算得陶瓷室温弹性模量,但三点弯曲试验在高温下的应用由于挠度变形难以准确测量而鲜有报道。本研究基于相对法理论,提出了挠度修正法,可以方便准确地获得其高温弹性模量。采用电感量仪与挠度修正法测试了2D与3D C/C复合材料室温弹性模量,结果表明2种方法的测试结果相近。测试了C/C复合材料在室温至1700℃间的弹性模量,结果表明2D与3D C/C复合材料的弹性模量均在1200℃时达到最大值82.22 GPa、66.73 GPa;而后在1200~1700℃,随着温度的升高,其弹性模量逐渐降低,且2D C/C复合材料的降低幅度更大。本研究显示挠度修正法可以准确、可靠地评价碳/碳复合材料的高温弹性模量,有望推广应用于其它高温结构材料弹性模量测量领域。     

提高纳米复合陶瓷刀具材料力学性能的方法

纳米复相陶瓷刀具材料的研究成功有望从根本上解决陶瓷材料的脆性问题,比起传统刀具陶瓷刀具材料,它具有更高的抗弯强度、断裂韧度等力学性能.介绍了纳米复相陶瓷的增韧补强机理;对研制高性能纳米陶瓷刀具材料需考虑的主要因素进行了探讨.     

含孔隙多相纳米晶体陶瓷的力学性能计算模型

提出一个晶粒与晶界的混和模型，用于计算单相纳米晶体陶瓷的弹性模量，进而结合Budiansky等人的自洽模型计算了含孔隙多相纳米晶体陶瓷的弹性模量。在此基础上，将正割模量替代弹性模量，在等应变假设的前提下，将提出的能计算含孔隙多相纳米晶体陶瓷弹性模量的模型拓展成能描述该类材料在小塑性变形条件下的应力-应变关系的模型，并且确定σ0．2为含孔隙多相纳米晶体陶瓷的屈服强度。大量计算结果与试验数据的对比表明，所提出的模型能较好地反映晶粒尺寸与孔隙率对纳米晶体陶瓷弹性模量与屈服强度的影响。     

陶瓷涂层断裂韧性的表征

由于陶瓷本身的脆性,陶瓷涂层的应用受到了极大的制约。断裂韧性是反映材料抵抗裂纹失稳扩展能力的力学性能指标,陶瓷涂层因为脆性和低维特点,对其断裂韧性的表征存在较大困难,目前主要有临界应力强度因子KⅠC、临界裂纹扩展能量释放率GⅠC和裂纹密度β三种表征方法。本文对上述方法进行了总结、分析。     

LaB_6和La_2O_3添加剂对ZrB_2-SiC超高温陶瓷结构与性能的影响

采用SPS工艺制备添加La_2O_3或LaB_6的ZrB_2-SiC陶瓷,测量试样的密度和力学性能,利用扫描电镜和透射电镜观察试样的微观形貌,研究添加镧的不同化合物对ZrB_2-SiC陶瓷显微结构和力学性能的影响,分析添加量对材料力学性能的影响.同时对ZrB_2-SiC-La_2O_3和ZrB_2-SiC-LaB_6陶瓷进行热处理,考察热处理对其力学性能的影响.结果表明,加入2.5%或5%(质量分数, 下同)的La_2O_3或LaB_6添加剂后,材料的室温强度、高温强度、断裂韧性都比无添加剂时要高;当含量相同时,加入LaB_6比La_2O_3更有利于提高陶瓷材料的室温强度;当添加剂的含量为2.5%时,材料的室温强度比较好,当添加剂的含量为5%时,材料的高温强度和断裂韧性比较高.热处理可以提高ZrB_2-SiC-La_2O_3和ZrB_2-SiC-LaB_6陶瓷材料的高温强度.     

含孔隙纳米晶体材料力学性能的计算模型

针对纳米晶体材料的微观结构,构建了一种复合相本构关系来描述纳米晶体材料的力学性能。纳米晶体材料由晶粒和晶界两部分组成,其中晶界相又包含两部分:晶界第一部分与晶界第二部分。晶界第一部分与晶粒应变相等,这两者的结合体又与晶界第二部分是等应力的,这更符合纳米晶材料的实际变形情况。然后,建立的模型被用以计算含孔隙纳米晶体材料的弹性模量,并将提出的计算含空隙纳米晶体材料弹性模量的模型拓展为描述纳米晶体材料小塑性变形条件下的应力-应变关系。计算结果与试验数据相比较表明,本模型可以较好地反映晶粒尺寸和孔隙率对纳米晶体材料弹性模量与屈服强度的影响。     

无压烧结SiBON陶瓷的组织结构与力学性能

利用熔石英,六方氮化硼和氮化硅陶瓷粉末,通过冷等静压成型和在不同温度下进行无压烧结的方法制备了SiBON陶瓷复合材料,并对其进行了力学性能测试,分析了材料的物相组成与结构。实验结果表明:通过这种简单高效的工艺可以制得性能较好的SiBON陶瓷复合材料,且可通过控制材料组分和烧结温度调整材料的力学性能,其中,材料的致密度在67.3%～98.4%,抗弯强度为60～170 MPa,断裂韧性为0.8～2.1 MPa.m1/2,弹性模量为48～112 GPa。     

机械系统可靠性定量评价方法

随着机械产品结构和工作环境日益复杂,机械系统可靠性的正确评估对产品质量评价和全寿命周期管理具有重要的现实意义。简要介绍机械可靠性定量模型的建模原理、研究现状和存在的问题,指出尽管静态系统可靠性模型相对成熟,对传统应力强度干涉模型进行扩展可解决大部分机械零部件及机械系统的可靠性评估问题,但是,当机械零部件强度退化时,机械系统可靠性分析需要考虑时间因素,传统静态模型无法满足时变可靠性分析要求。因此,着重阐述了机械系统时变可靠性模型建模过程中有待解决的关键问题。     

MSP试验法评价MoSi2系复合材料高温力学性能

采用MSP（Modified Small Punch）试验法对MoSi2系复合材料的高温力学性能进行评价，不仅能方便地得到各组分复合材料高温强度随温度的变化，还能得到各组分复合材料的脆性延性转变温度，其结果和材料的微观结构相对应。对MoSi2系复合材料高温蠕变测试表明，MSP试验法得到的蠕变曲线和传统方法类似，而且随着氧化物添加相含量的增加，复合材料的高温蠕变性能下降。MSP试验法评价陶瓷材料的高温力学性能方便有效。     

Evaluation of mechanical performance of NiCo nanocoated aerospace aluminum alloy using quantitative photo-thermo-mechanical radiometry as a non-contact strain gauge

Non-contact photo-thermo-mechanical radiometry (PTMR) was introduced to evaluate the mechanical properties of an aerospace aluminum alloy with Nickel Cobalt (NiCo) coatings. A home-made small-scale tensile rig was used to apply static uniaxial tensile load on the samples. The strength of nanocoated samples was recorded in terms of strain by an adhesive strain gauge also acting as a PTMR calibration device. For the purpose of non-destructive evaluation, the tests were limited within the elastic regime. Two experimental modalities were used: frequency scan at fixed load and strain scan at fixed frequency. The test results were analyzed with both a three-layer and a more detailed five-layer thermo-mechanical-wave (TMW) model. Both theoretical and experimental results indicated that the presence of the NiCo nanocoating can significantly strengthen the mechanical properties of the coated aluminum substrate. The coating can also provide protection to defective substrates and enhance their mechanical stiffness (strength).     

Evaluation of high-temperature tensile properties of Ti-6Al-4V using instrumented indentation testing

Since materials used in or exposed to high-temperature environments can undergo variation or degradation of mechanical properties, it is important to evaluate mechanical properties at high temperature, in particular for structural applications and aerospace materials. Instrumented indentation testing (IIT) is widely used to evaluate such mechanical properties of materials as tensile properties, residual stress, fracture toughness, etc., exploiting theoretical approaches to indentation mechanics. In this study, we used IIT to evaluate variations in tensile properties with temperature of the Ti alloy Ti-6Al-4V, a candidate material for aerospace applications, using a high-temperature chamber and a modified representation method. Comparison of our results with conventional uniaxial tensile test results showed good agreement (within a 10% error range) in yield strength and ultimate tensile strength. This confirms the potential of IIT for evaluating to evaluate high-temperature tensile properties of metallic materials and for research on material behavior in various temperature conditions.     

Cross-sectional nanoindentation and nanoscratch of compositionally graded mullite films

Nanoindentation and nanoscratch have become well-established techniques for measuring mechanical properties of thin films. Conventionally, these tests are performed on the surface of the films to evaluate their mechanical integrity: elastic modulus, hardness and adhesion strength. However, in complex systems such as compositionally graded thin films, small spatial variations in mechanical properties are difficult to distinguish using this approach. In this work, the evaluation of the above parameters was conducted on cross-sections of compositionally graded mullite coatings, chemical-vapor deposited on silicon carbide substrates. To assess the intrinsic mechanical properties and their spatial variation, nanoindentation tests were carried out on mullite coatings with constant and graded Al/Si ratios. Additionally, transverse nanoscratch tests to evaluate the cohesive and adhesive resistance of the coatings as well as the coating/substrate systems, respectively, were performed. Different damage morphologies were identified within the coating and at the interface by using complementary characterization techniques. In the case of functionally graded coatings a gradual rise in the hardness and elastic modulus with increasing distance from the coating/substrate interface was observed. Nanoscratch tests on the cross-sections allowed determining the critical loads for cohesive and adhesive damage by following this approach. Compositionally graded mullite coatings exhibited the best combination of hardness/stiffness and cohesive/adhesive scratch strength.     

冷却速度对C-Si-Mn系热轧双相钢组织性能的影响

通过实际的热轧实验,研究了轧后冷却速度对C-Si-Mn系热轧双相钢组织形貌和力学性能的影响。研究发现,轧后冷却速度对热轧双相钢的显微组织和力学性能有很大的影响。热轧双相钢具有三种典型的组织形貌,而不同的组织形貌通过不同的强化机制赋予热轧双相钢不同的力学性能。通过不同冷却速度下的双相钢热轧实验,可以使热轧双相钢获得良好的力学性能。     

Rotating strength of forged TiAl alloys

In order to evaluate the rotating strength of TiAl alloys, mechanical and rotating burst testing were conducted on wrought TiAl having various microstructures. The rotating burst strength of the nearly lamellar (NL) structure was greater than near gamma (NG) or fully lamellar (FL) structures. The mechanical properties which have an affect on the rotating strength were yield strength and elongation, and only a slight amount of elongation allows the rotating burst characteristics of TiAl alloys to change from ceramic-like maximum stress dependency to metal-like mean stress dependency. It was estimated that forged NL–TiAl has greater rotating strength above 1000 K than superalloys in current use.     

Structure–property correlation of EN steel and evaluation of mechanical properties through BIT

The present studies deal with the evaluation of mechanical properties through Ball Indentation Technique (BIT) for En steel, having varying microstructure due to specific heat treatment imparted. Investigations have been carried out on four types of failed shaft materials. The dependence of yield strength (YS), ultimate tensile strength (UTS), strength coefficient (K) and strain hardening exponent (n) values on various microstructural features is studied using the BI technique and the results are validated with the standard conventional test results. It is found that indentation diameters (plastic) measured by linear variable displacement transducer (LVDT) are slightly less than the diameters measured by optical microscope and this is due to pile-up/sink-in of materials surrounding the indentations. So the determination of mechanical properties, using LVDT measured depth, requires addition of correction factor for getting actual contact diameter. This structure–property correlation study clearly proved the effectiveness of the BI set-up to find the small changes in mechanical properties due to heat treatment on the same group of material.     

基于神经网络方法的焊接接头力学性能预测

针对焊接过程严重非线性和焊材中多种成分的复杂交互作用使得对接头力学性能的准确估算十分困难的实际问题,论述了神经网络技术在焊接接头力学性能预测方面的应用。研究了神经网络建模方法,提出采用均匀设计法优化设计神经网络参数,在四类17种钢材的焊接热模拟数据基础上,建立了预测焊接接头力学性能的神经网络模型。试验表明该模型可根据钢材成分和焊接规范对焊接接头及其热影响区的冲击韧度、抗拉强度、屈服强度、断面收缩率和硬度等力学性能进行较为准确的估算。试验表明,该预测方法较之传统统计方法,预测精度有了大幅度提高,为实现焊接接头力学性能预测提供了一条有效的途径。     

Modelling and simulation of local mechanical properties of high silicon solution-strengthened ferritic compacted graphite iron

This study focuses on the modelling and simulation of local mechanical properties of compacted graphite iron cast at different section thicknesses and three different levels of silicon, ranging from about 3.6% up to 4.6%. The relationship between tensile properties and microstructure is investigated using microstructural analysis and statistical evaluation. Models are generated using response surface methodology, which reveal that silicon level and nodularity mainly affect tensile strength and 0.2% offset yield strength, while Young′s modulus is primarily affected by nodularity. Increase in Si content improves both the yield and tensile strength, while reduces elongation to failure. Furthermore, mechanical properties enhance substantially in thinner section due to the high nodularity. The obtained models have been implemented into a casting process simulation, which enables prediction of local mechanical properties of castings with complex geometries. Very good agreement is observed between the measured and predicted microstructures and mechanical properties, particularly for thinner sections.