延性断裂韧度JⅠC测试中的钝化线方程

钝化线是描述裂纹试样在钝化过程中J积分与伸张区宽度(stretch zone width,SZW)间关系的一条直线,在J积分测试中,有效数据区的左右界限线以及确定延性断裂韧度JⅠC的偏置线都是建立在钝化线基础上的,因而钝化线在J积分测试中至关重要。通过对裂尖钝化过程的分析,基于D-B模型和J积分的路径无关性原理推导出一种钝化线方程。与现行标准中的钝化线相比,此方程与试验结果吻合得更好。     

对J积分测试方法中几个问题的讨论

针对延性断裂韧度JIC测试中遇到的困难，讨论现行，积分测试标准中关于最小裂纹扩展线和对裂纹扩展阻力JR值的上限限制及JIC的定义.研究认为，不同金属具有不同的裂纹钝化特征，钝化线方程取决于材料的强度、塑性和应变强化能力。测试标准中规定的钝化线方程只与材料强度水平有关，而且斜率太低，不能准确描述裂纹的钝化行为，进而以此钝化线为基础设置最小裂纹扩展线，并用它排除裂纹未真实扩展的试验数据势必造成某些不准确判断。因此，在提出合理的钝化线方程之前，建议采用下列原则处理J积分测试结果：J=1．5(σa σb)△α作为钝化线方程；由钝化线向右偏置0．03mm的平行线作为最小裂纹扩展线；Ja≤b0σY／15作为测试数据的有效性条件。另外对饱和伸张区(critical length of the stretched zone width，SZWC)的测试结果表明，钝化线与JR曲线交点所对应的J值即Ji可定义为延性断裂韧度JIC。文中还比较了不同研究者报告的16Mn钢测试结果的差别，并分析造成差别的原因。     

对JⅠC测试标准的部分修订内容的合理性讨论

讨论现行JⅠC测试标准中存在的不适应性,认为裂纹试样受力后的钝化过程不仅取决于材料的强度,而且还受材料形变强化特性的影响;钝化线方程应充分考虑裂纹钝化过程中裂尖材料的形变强化特性,钝化线的合理性决定于其在多大程度上能够真实反映裂纹的实际钝化过程,指出修订的GB/T 2038-1991在实际J积分测试中遇到困难的主要原因不仅在于规定的钝化线斜率太低,而且还与以钝化线为基础设置最小裂纹扩展线的偏置量太大、规定的有效数据范围稍嫌苛刻等因素有关.文中还对不同研究者采用的JⅠC测试技术进行对比分析,对JⅠC测试方法的进一步完善提出一些建议.     

对J1c测试标准的部分修订内容的合理性讨论

讨论现行J1c测试标准中存在的不适应性,认为裂纹试样受力后的钝化过程不仅取决于材料的强度,而且还受材料形变强化特性的影响;钝化线方程应充分考虑裂纹钝化过程中裂尖材料的形变强化特性,钝化线的合理性决定于其在多大程度上能够真实反映裂纹的实际钝化过程,指出修订的GB/T 2038-1991在实际J积分测试中遇到困难的主要原因不仅在于规定的钝化线斜率太低,而且还与以钝化线为基础设置最小裂纹扩展线的偏置量太大、规定的有效数据范围稍嫌苛刻等因素有关.文中还对不同研究者采用的J1c测试技术进行对比分析,对J1c测试方法的进一步完善提出一些建议.     

一种确定延性金属静动态启裂点的新方法

在静动态J积分试验的基础上,应用曲线分析技术确定该钢的静动态启裂点.研究表明,在静动态J积分试验中,预制裂纹钝化、启裂到稳态扩展的过程是裂纹前沿由塑性滑移变形主导的钝化阶段与由微孔形核、长大与连结主导的延性断裂阶段发展的连续过程,启裂点实际上是这两个阶段之间的过渡点,它与lg J-lg Δa曲线上的转折点相对应.由此方法确定的静动态启裂位置均与断口上实测的临界伸张区宽度吻合得较好.     

计算贯穿裂纹疲劳J积分范围和蠕变J积分范围简化方法的改进

为了检查表征疲劳和蠕变疲劳裂纹特征的J积分计算方法精度进行了一系列试验。结论为:(1)在计算疲劳J积分中,用循环应力应变方程代替Kumar的J积分方程中的稳态应力应变方程,可提高简化方法的精度。(2)在计算蠕变疲劳J积分中,用循环载荷保持过程中近似表征蠕变行为的蠕变方程代替Norton形式的蠕变方程,可提高简化方法的精度。     

关于动态钝化线方程与J-R法确定JId的讨论

在摆锤式示波冲击试验机上采用小角度冲击方法测试了某船用低舍金钢的动态弹塑性断裂韧度JId。针对多试样,R阻力曲线法因钝化线的不易确定性常造成测试结果JId误差较大的情况,考虑了加载速率对塑性流变应力的影响,给出了一新的动载争件下的钝化线方程：J-2NK（0．5Er）^nΔα。在J-R阻力曲线法测定材料的JId时,用该方程可得到与小角度冲击方法相一致的测试结果。     

用线弹性和弹塑性方法确定断裂韧性

用线弹性和弹塑性方法测定了二种Ni-Cr-Mo钢的断裂韧性,从对线弹性/理想塑性的载荷位移曲线的计算以及从实验结果得知:应该采用Merkle和Corten关系来计算紧凑拉伸试样的J积分。用来确定临界J值的外推法,含有某些问题。作为一种选择,建议测定离钝化线一个固定距离的J。从J计算的以及从线弹性方法计算的应力强度因子之间的比较表明:线弹性断裂力学可以使用比金属材料平面应变断裂韧性试验方法ASTM(E 399-74)所规定的尺寸小得多的试样。等价能量法和用不同的夹式仪在离裂纹尖端的不同距离处测定的裂纹尖端张开位移给出了与J积分方法一致的应力强度因子。     

焊接接头断裂性能的试验研究

为了理解材料及几何组配，对不同应力状态条件下不同几何构形的焊接接头试件的J积分的作用和影响，对单边裂纹板远场均匀拉伸条件下焊接试件的临界J积分进行实际测试。结果表明，试件未开裂之前，在同一载荷的作用下，焊接接头的J积分参量、加载点位移△以及裂纹嘴张开位移CMOD值介于全母材和全焊缝材料测试值之间，并且低组配焊接接头的J积分参量依照全母材、焊接接头和全焊缝的次序依次递减，而高组配则与低组配正好相反。不同材料组配焊接接头的J积分值，在焊接疑宽度较小时，与其全母材的J积分测试结果较为接近；而在焊缝宽度参数较大时，与全焊缝材料结果的差别较小。因此，在进行焊接接头的J积分值测试时必须考虑焊缝宽度参数的影响。     

ASTM和ISO标准断裂韧度测试方法比较研究

ASTM E1820-11和ISO 12135-2002标准是测试断裂韧度的主要标准,然而这两个测试标准在钝化线、有效数据区间和阻力曲线拟合等方面存在较大的差异,导致断裂韧度测试结果的较大不同。研究这两个测试标准钝化线的依据,比较它们的差异。ASTM标准采用理想弹塑性材料假设,ISO标准基于材料的真应力应变关系满足幂次定律,ISO标准钝化线斜率比ASTM标准钝化线斜率大;ASTM标准采用两参数方程阻力曲线,而ISO标准采用三参数方程阻力曲线。提出根据材料应力应变特性来选择合适的试验标准,对于带屈服平台的材料可选用ASTM标准,不带屈服平台的材料可选用ISO标准。选取Q345R钢进行断裂韧度试验,用ASTM和ISO两个标准对试验结果进行评估,试验结果表明:Q345R的应力应变曲线在屈服阶段存在屈服平台,ASTM钝化线能更好反映裂纹尖端钝化。ASTM和ISO两个标准测得的断裂韧度分别为235.29 kJ/m~2和179.37 kJ/m~2,两者相差24%。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.