Estimation of fatigue crack growth behavior for small-sized C-shaped inside edge-notched tension (CIET) specimen using compliance technique

Being restricted by the relative larger size requirement, traditional and standard fracture specimens are not applicable for the estimation of fatigue crack growth behavior of some very finite-sized components and precious materials. This study develops a small-sized C-shaped inside edge-notched tension (CIET) specimen which has an advantage of specimen minimization and a wide range of adaptability. A systemic compliance technique for estimating fatigue crack growth behavior of CIET specimen has been successfully constructed and experimentally verified. Groups of fatigue crack propagation rate tests of both CIET specimen and CT specimen for 5083-H112 aluminum alloy were carried out. The resulted da/dN ∼ ΔK curves are heavy affected by specimen configuration and load ratio, and the difference between these da/dN ∼ ΔK curves has been successfully removed by introducing the correction of plasticity-induced crack closure effect. Consequently, the feasibility of CIET specimen for estimating fatigue crack propagation behavior for small-sized components and precious materials has been evidently confirmed.     

辐照用小尺寸样品力学性能表征技术研究进展

由于辐照空间尺寸限制、降低样品放射性和提高辐照参数精度等原因，小尺寸样品被广泛应用于核反应堆材料的辐照后力学性能表征。本文就国内外小尺寸拉伸、冲击、断裂韧性、疲劳、蠕变和小冲杆等测试表征技术的研究现状进行了综合论述，分析了小尺寸样品测试中的关键影响因素以及数据归一化方法，总结了小尺寸样品存在的问题，并结合我国需求对小尺寸样品技术的发展进行了分析和展望，以期为小尺寸样品技术及测试分析数据进一步规范化和工程应用发展提供参考。     

Shear Plugging and Frictional Behaviour of Composites and Fabrics Under Quasi‐static Loading

Experimental studies are presented on the shear plugging and frictional behaviour of composites and fabrics under quasi‐static loading. The primary focus is on the effect of specimen thickness on quasi‐static shear plugging behaviour. In the present study, quasi‐static shear plugging and through‐the‐thickness frictional tests are carried out on three types of materials. The materials investigated are 2D plain weave E‐glass/epoxy, 2D plain weave T300 carbon/epoxy and 2D plain weave E‐glass fabric. Typical results on shear plugging strength and frictional behaviour are presented. Effect of specimen thickness on quasi‐static shear plugging behaviour is also investigated.     

影响水泥抗压强度的成型条件研究

水泥抗压强度的测定过程有成型、养护、破型三个主要环节。各环节的试验条件不同,将直接影响抗压强度的测定结果。研究了水泥试件成型过程中流动度、试件尺寸、表面状态等试验条件对试件抗压强度测定结果的影响。结果表明：在一定范围内水灰比与抗压强度呈正相关关系,即水灰比越大,其流动度越好,抗压强度越高,当超过这个范围后,随着水灰比的增大,抗压强度逐渐减小;随着试件尺寸逐渐变大,抗压强度依次降低;试模涂油量多少不同,导致试件表面状态存在差异,涂油量过多或过少都会使抗压强度的测定结果偏低。     

Evaluation of Tensile and Fatigue Properties of Metals Using Small Specimens

Small specimens are increasingly being used in getting mechanical properties directly when there are limited materials to facilitate standard specimens, which play a great role in the rapid measurement of mechanical properties and residual life assessment of in-service reactor components. Although tensile and fatigue properties of the small specimens are investigated extensively, theoretical models for describing the mechanical properties of small specimens need to be established. Here, we conduct a systematic investigation of tensile and fatigue properties of pure Cu specimens with thicknesses ranging from 3 to 0.2 mm. The results show that the decrease in uniform elongation of the 0.2 mm-thick specimens is mainly due to the effects of grain boundary and free surface on the strain hardening rate. A modified theoretical model correlated with the ratio of the surface grain layer thickness to the grain size is proposed to predict variation in yield strength of the small specimens more accurately. Furthermore, the mechanism for the difference in fatigue life between the 0.2 mm-thick specimen and other thicker specimens is elucidated. The Basquin equation-based model is presented as a potential way to evaluate the fatigue life of metals using small specimens.     

后置翼墙加固框架柱抗震变形能力研究

为考察后置翼墙加固混凝土框架柱的抗震性能,结合已有研究中试验轴压比为0.31、0.36、0.40,原柱纵筋配筋率为0.82%~1.23%的18个后置翼墙加固试件的低周反复荷载试验,采用ABAQUS软件进行了675个后置翼墙加固试件在水平反复荷载下的有限元模拟。试验和有限元分析结果表明：由于后置翼墙作为原柱的耗能及加固部件有效保护了原柱,后置翼墙加固试件中原柱损伤相对较轻;后置翼墙一字形加固柱的损伤主要发生在两片后置翼墙端部区域,T形及L形加固柱原柱损伤主要发生在未后置翼墙一侧,且损伤区域较小;建立了翼墙加固柱极限层间位移角关于原柱轴压比、剪跨比、翼墙钢筋配筋率等关键参数的计算式。     

用短棒试件测试无烟煤准静态断裂韧度试验研究

根据国际岩石力学学会建议采用的岩石断裂韧度测定方法,用短棒试件在Instron 1342型电液伺服控制材料试验机上测定了无烟煤准静态I型断裂韧度,其断裂韧度值在位移速率较低时提高较大,但随位移速率的提高有逐渐趋于稳定的趋势。从载荷-COD曲线图中分析了无烟煤断裂时,载荷出现跳动的原因,根据载荷跳动情况可以确定三角形韧带开始起裂时间。根据计算结果得出:试件加工几何上的误差对无烟煤断裂韧度值影响不大,造成的误差最大只有2.4%;但对弹性模量值的影响较大,造成最大的误差达到13.3%,同时用图解法得到了无烟煤的非线性度大于0.4。     

普通混凝土配合比设计及其强度检测问题的探讨

结合工程实例,从试验检测的角度,分析了普通混凝土配合比设计、试件取样及其现场强度检测方法取舍等方面存在的问题与所应采取的基本措施.     

离心成型钢纤维混凝土抗冻性试验研究

通过对离心成型钢纤维混凝土试件的抗冻试验,研究了基体混凝土强度和钢纤维体积率对离心成型混凝土抗冻性能的影响规律,探讨了试件尺寸对抗冻试验结果的影响。研究结果表明:单纯提高基体混凝土强度不能明显改善离心成型混凝土的抗冻能力,掺入钢纤维则显著提高了离心成型混凝土的抗冻能力,并且钢纤维掺量的增大使离心成型混凝土的抗冻能力增强。结合离心成型钢纤维混凝土构件的纤维分布规律,对上述试验结果进行了分析讨论。     

用平台巴西圆盘试样确定脆性岩石的弹性模量、拉伸强度和断裂韧度——第一部分:解析和数值结果

用平台巴西圆盘试样在一次试验中同时测定脆性岩石的弹性模量E、拉伸强度ts和张开型断裂韧度IcK。根据应力分析的结果和Griffith 强度准则,为了保证试样在加载过程中由中心部位起裂,平台对应的加载角必须大于一个临界值(a2≥20°),并以此条件确定平台的最小相对宽度。理论分析表明,可以根据记录的载荷-位移破坏全过程曲线(包括最大载荷之后过程的记录),由初始直线段确定E,由最大载荷确定ts,由紧随其后的最小载荷确定IcK。给出E,ts和IcK相应的计算公式,公式中的关键参数由严格的有限元分析标定。还给出了一些基于弹性力学的近似解析公式,它们的精度也用有限元分析做了验证,因此,利用这些公式所得的结果是可靠的。