钢板表面纵向裂纹的金相检验和分析

在连铸轧制的钢板表面有沿轧制方向的裂纹。采用化学成分分析,宏、微观检验等方法对裂纹进行了分析。结果表明,裂纹中存在氧化物及其脱碳等缺陷,这说明连铸坯表面在轧制前已存在裂纹并在轧前加热中裂纹内发生氧化和脱碳,导致轧制后的钢板表面出现裂纹。     

高层建筑用Q345GJC钢板表面裂纹成因分析

采用宏观分析、化学成分分析、金相检验、扫描电镜观察和能谱分析等方法对某批轧制后表面存在纵向裂纹的高层建筑用Q345GJC钢板的裂纹形成原因进行了分析。结果表明:钢板表面裂纹在连铸板坯上就已经存在,裂纹产生的主要原因是在连铸过程中结晶器涂层严重磨损致使铜板外露,从而使铜元素渗入到连铸板坯中,降低了钢的热塑性,导致了裂纹的产生;在随后的轧制过程中,裂纹沿轧制方向进一步扩展形成纵向裂纹。     

轧制组织对镁合金AM60疲劳性能的影响

研究了AM60轧制后挤压镁合金的组织对其机械性能和疲劳裂纹扩展性能的影响。实验表明:轧制使晶粒细化,强度显著提高。沿纵轴轧制方向出现大量等轴李晶组织,而在横向原来的孪晶组织消失。对于存在大量孪晶组织的方向,其抗拉强度明显低于其它方向。轧制AM60的横向疲劳裂纹扩展速度(FCPR)明显地高于纵向。当疲劳裂纹尖端塑性区的尺寸与组织的晶粒度接近时,挤压AM60组织中晶粒大小的不均匀引起裂纹分叉,裂纹分叉和粗糙度诱发的裂纹闭合对疲劳裂纹扩展产生严重的阻滞作用在挤压镁合金AM60的疲劳裂纹扩展速度(da/dN)与应力强度因子范围(△K)的关系曲线上出现拐点(△K=64～7.5 MPa·m~(1/2))。疲劳裂纹扩展为沿晶和穿晶混合方式。     

60kg／m级钢轨表面起皮缺陷分析

60kg／m钢轨在使用一段时间后表面出现起皮缺陷。采用金相检验和低倍检验等方法对表面起皮钢轨的显微组织和低倍特征等进行了分析和研究。结果表明,起皮缺陷的形成是由铸坯角部裂纹和中间裂纹所引起的。并提出了改进措施。     

高速齿轮轴齿表面凹坑产生原因分析

高速齿轮轴在经过渗碳和淬、回火热处理后的喷丸过程中,其齿部表面出现多处凹坑。利用光学显微镜、扫描电子显微镜、直读光谱仪和显微硬度计等对齿部表面的凹坑进行了失效分析。结果表明：齿部表面的凹坑区域存在沿晶扩展的微裂纹,另还存在沿晶界分布的碳化物;表面出现凹坑是由于在渗碳后的空冷过程中表面产生了“⊥”型裂纹,在随后的停放期间和等温淬火时“⊥”型裂纹沿轴向或径向进一步扩展形成剥离裂纹,继而于喷丸过程中表层断裂脱落,产生凹坑。     

中厚板材表面纵裂纹成因分析

用光学显微镜和电子显微镜对中厚板轧后出现的表面纵裂纹进行了观察和分析。发现钢板横截面上的裂纹都有向内扩展的趋势．在裂纹面和裂纹周围都存在夹杂物，且夹杂物成分中有结晶器保护渣的特有成分钠和钾；裂纹面上有大量气泡，沿轧制方向呈簇状分布。因此认为，凡影响初生坯壳凝固均匀性的因素对纵裂纹的产生都有影响，其中保护渣的性能和皮下气泡是钢材产生表面裂纹的主要原因。     

铜／铝冷轧复合板剥离性能及界面摩擦分析

采用同步轧制方法制备铜／铝复合板,研究了轧制变形量对于铜／铝复合板结合强度和剥离表面形貌的影响,分析了轧制复合界面摩擦机理。研究结果表明,复合板结合强度、剥离表面粘铝、铜基体表面裂纹数都随着轧制变形量的增大而增大。变形量为50％时,结合强度为2N／mm,变形量为60％时,结合强度为7N／mm,变形量为70％时,结合强度为14N／mm。轧制过程中,新鲜金属从结合面裂纹中挤压出来,受界面摩擦力剪切作用,两新鲜金属搓合在一起形成良好结合。     

圆钢纵裂分析

针对进口的45铜在连铸坯轧制大规格圆铜(≥Ф160mm)时产生的纵向裂纹．借助扫描电镜，从裂纹形态等方面进行了观察和分析。结果表明，圆钢的裂纹内部有夹杂物，两侧有脱碳现象，裂纹末端沿铁素体偏析带延伸．偏析带内部也存在夹杂物，由此证实，原材料中存在的成分偏析带以及偏析带内的夹杂物是导致轧制后圆钢纵裂的根本原因，     

42CrMo钢蜗杆开裂原因分析

42CrMo钢蜗轮蜗杆在装配时发现蜗杆表面开裂,通过宏观分析、化学成分分析、淬火表面残余应力测试、微观分析、金相检验、能谱分析、硬度测试等方法对蜗杆开裂的原因进行了分析。结果表明:该42CrMo钢蜗杆表面裂纹为淬火应力裂纹,蜗杆材料中的锰的质量分数偏高以及淬火过程中热应力与组织应力叠加导致蜗杆沿轴线方向开裂。     

65Mn直缝焊管开裂原因分析

本文对65Mn钢带在制作直缝焊管时出现开裂的原因进行了分析。采用金相显微镜和扫描电镜对开裂部位和未开裂部位试样的组织、断口形貌进行观察,结果表明：钢带在纵剪分条时边缘出现微裂纹,该微裂纹在弯管成型过程中进一步扩展导致开裂。     

Effect of thermal mismatch induced residual stresses on grain boundary microcracking of titanium diboride ceramics

The effect of thermal mismatch induced residual stresses on grain boundary microcracking in titanium diboride (TiB₂) ceramics has been studied by finite element method. A cohesive zone model was used to simulate the microcracking initiation in four-point bending specimens. In particular, the microcracking was assumed to occur at a grain boundary which is located in the center of the specimen, surrounded by a thermally anisotropic area. The predicted failure strength appears to be significantly reduced by the presence of residual stresses when the cohesive energy of the microstructure is small. The failure load from experiments has been used to determine the critical damage parameters for microcracking initiation in both pristine and aluminum-infiltrated TiB₂. A viscous regularization technique is employed in the simulations to improve the rate of convergence of the solution and the effect of the value of the viscosity parameter on the simulation results, has been investigated. The effect of grain size, grain orientation, and number of employed thermally anisotropic grains, on the microcracking is also discussed.     

The extent of microcracking and the morphology of microcracks in damaged bone

Strain-induced damage in bovine laminar bone has been examined using laser scanning confocal microscopy (LSCM). The specimens were loaded in a fluorescein solution, which penetrated the newly formed cracks in the specimen. The microcracking, and the larger cracking, induced by strain were very clearly visible. The microcracking occurred diffusely in regions of high strain (stress), but was particularly obvious in the vicinity of large machined stressconcentrators. The microcracking could be shown not to be artefactual, that is, it was produced by strain, and not by specimen preparation. The microcracking interacted with the structure of the bone, often having a wavy appearance related to the histology. Microcracks seemed to be particularly associated with the most highly mineralized parts of the bone. LSCM is a technique holding great promise for the investigation of the initiation and development of damage in mineralized hard tissues, and other translucent materials.     

Microcracking and porosity in calcium phosphates and the implications for bone tissue engineering

Calcium phosphates including hydroxyapatite (HA) have been widely studied as bone scaffold materials. However their mechanical properties are highly variable and may be a function of thermal expansion anisotropy (TEA) induced stresses and microcracking. There is confusion concerning the mechanisms and microscopic identification of microcracks in HA. This study presents clear evidence of microcracking from micrographs of as-sintered HA surfaces which avoids the complications of identifying TEA-induced microcracks on fracture surfaces. Additionally, the existing literature of TEA-induced microcracking is briefly reviewed and pertinent papers involving likely microcracking in HA are analyzed. The recent realization in the biomedical literature notes that microcracks are of critical importance in remodeling and repair of damaged bone tissue. Hence, the similarities between microcracking in HA used for scaffolds in bone tissue engineering and that in the normal bone repair process is of importance in designing HA scaffolds with improved mechanical properties and biocompatibility.     

On the phenomenon of curved microcracks in [(S)/90n]s laminates: Their shapes, initiation angles and locations

A variational analysis of the stress state in microcracked cross-ply laminates has been used to investigate the phenomenon of curved microcracking in [(S)/90_n]_s laminates. Previous investigators proposed that the initiation and orientation of curved microcracks are controlled by local maxima and stress trajectories of the principal stresses. We have implemented a principal stress model using a variational mechanics stress analysis and we were able to make predictions about curved microcracks. The predictions agree well with experimental observations and therefore support the assertion that the variational analysis gives an accurate stress state that is useful for modeling the microcracking properties of cross-ply laminates. An important prediction about curved microcracks is that they are a late stage of microcracking damage. They occur only when the crack density of straight microcracks exceeds some critical value-the critical crack density for curved microcracking. The predicted critical crack density for curved microcracking agrees well with experimental observations.     

Observation of fracture process zone by laser speckle technique and governing mechanism in fracture of concrete

Fracture tests with a wedge-loading device are carried out on mortar and concrete specimens so as to have stable crack growth. Using laser speckle technique the length of macrocrack and the distribution of crack opening displacement are measured. Results are compared with those obtained by the boundary element method (BEM) analysis for a Dugdale-Barenblatt-type model of a fracture process zone. The governing mechanism in fracture of concrete and the mechanism which is represented by the model are discussed with special attention to the microcracking zone. It is deduced that a Dugdale-Barenblatt-type model does not represent the microcracking zone, thus implying that the microcracking zone and the bridging zone correspond to the pre-peak nonlinear part of the stress-strain curve in a uniaxial tension test and the post-peak tension-softening curve, respectively. It is concluded that the effect of microcracking on the maximum load is less significant than that of bridging. Possible models which include the effect of microcracking in addition to that of bridging are proposed.     

Mechanism of surface microcracking of matrix in glass-reinforced polyester by artificial weathering

The first stage in the deterioration of glass-fibre reinforced polyester (GRP) composites, fibre prominence, has been reported. The mechanism of the second stage, surface microcracking, is now described. Under controlled conditions GRP sheets were subjected to cyclic variation of moisture and temperature and to radiation. It is proposed that surface microcracking takes place under the combined action of radiation-induced tensile stresses in the surface region and physically-induced stress-fatigue. Tensile stresses in the surface region are caused by shrinkage of the matrix that results from cross-linking induced by the ultra-violet portion of radiation. Stress fatigue is imposed on the composite system by physically-induced alternating stresses produced by cyclic variation of temperature and, probably, moisture resulting from thermal and moisture gradients and inhomogeneities. Stress-fatigue probably plays a dominant role in microcracking induced by artificial weathering, whereas radiation-induced stresses in the surface region are more important in microcracking occurring in outdoor weathering.     

The thermal diffusivity and conductivity of transformation-toughened solid solutions of alumina and chromia

The thermal diffusivity of a series of solid solutions of alumina and chromia transformation toughened with a dispersed phase of unstabilized zirconia was measured by means of the laser-flash method from room temperature to 1400° C. It was found, in general, that the thermal diffusivity could be decreased significantly by the combined effects of solid solution alloying, microcracking and by the presence of the low conductivity dispersed phase of zirconia. The decrease in thermal diffusivity by microcracking was found to be present in the solid solution with low chromia content which underwent extensive grain growth. The effectiveness of solid solution formation and microcracking on thermal diffusivity was found to be greatest at the lower and intermediate ranges of temperature. The decrease in the thermal diffusivity due to the zirconia inclusions was found to be effective over the total temperature range. A numerical example is presented for the thermal conductivity calculated from the thermal diffusivity multiplied by the volumetric heat capacity.     

多方法融合的柑橘自动剥皮设备创新设计

目的设计一种能提高一次剥净率、降低果肉破损率的柑橘自动剥皮设备。方法提出一种多方法融合创新设计模型,并将其应用于柑橘自动剥皮设备的创新设计中。首先,根据Kano模型得到柑橘自动剥皮设备的用户需求属性;然后,结合公理设计理论完成域间映射,得到设计矩阵;由独立公理判断出设计矩阵类型,得到设计矩阵是准耦合设计,运用TRIZ理论进行解耦设计,得到柑橘自动剥皮机的创新设计方案;最后,结合层次分析法和模糊综合评价法对设计方案进行评价。结果利用该创新设计模型得到的柑橘自动剥皮机创新设计方案,在功能属性、安全属性和经济属性等3个方面都要优于现有的柑橘自动剥皮设备。结论设计的柑橘自动剥皮设备满足设计要求,验证了该创新设计模型的可行性及合理性。     

Matrix and fiber influences on the cryogenic microcracking of carbon fiber/epoxy composites

Cryogenic cycling effects on symmetric carbon fiber/epoxy laminates were examined using model prepreg systems. The properties of the composite materials studied were altered through the introduction of variations in their structure and composition. The curing agent used, matrix backbone flexibility, toughening agents, and longitudinal coefficient of thermal expansion of the reinforcing fibers were changed to investigate their role in cryogenic microcracking. Examination of the laminates after cycling provided insight into the mechanism and origins of thermal stress-induced microcracking. Matrix properties and fiber tensile modulus were shown to have a significant impact on the response of the composite materials to cryogenic cycling. It was found in this study that higher glass transition temperatures of the laminates and the presence of toughening agents in the matrix decreased the microcracking propensity of these laminates. Higher tensile moduli and linear coefficients of thermal expansion of the fibers were found to increase the microcrack density in the laminates studied.     

硅烷偶联剂对 EVA 太阳能电池封装膜 / 玻璃粘接性能的影响

研究了硅烷偶联剂类型以及层压温度对EVA太阳能电池封装膜/玻璃剥离强度的影响。发现含双键的硅烷偶联剂直接加入EVA胶膜可以有效提高剥离强度,但是剥离强度较低,对层压温度比较敏感,随着层压温度的提高而降低。然后采用底涂方法,即预先将玻璃表面用不同类型的偶联剂处理,再与不含硅烷偶联剂的EVA太阳能电池胶膜进行热压复合的方法,研究了硅烷偶联剂类型对剥离强度的影响。实验结果表明,含双键的硅烷偶联剂KH-570和Z-6032能非常有效地提高EVA胶膜与玻璃之间的剥离强度,而且其效果要明显好于未经硅烷偶联剂处理的玻璃与含硅烷偶联剂的EVA胶膜之间的剥离强度。同时发现,KH570等疏水性较好的硅烷偶联剂,能够有效地提高湿热老化(双85实验)条件下,EVA胶膜与玻璃之间的剥离强度。