科创中国

The strain distributions near the interface when the elbow steel fiber is pulled out from the half-mould concrete matrix are directly measured using a combined method of single fiber pull-out test and digital image correlation. Meanwhile, the real-time processes of the bonding, debonding and sliding at the interface are observed. The micro-mechanism of the strain localization in the failure process of interface when debonding occurs and the strengthening mechanism at the imbedded fiber are discussed. The experimental results show that the meso-scale strain localization gives rise to the localization of shear damage near the fiber interface. This strain localization characterized by the debonding process near the interface occurs, develops and moves gradually at an apparently regular interval. At the elbow part of the imbedded fiber, the peak value of the shearing stress occurs. But the primary debonding does not occur at this place because the strength of the shear damage is increased at the local area of the elbow part in the concrete, displaying an apparent reinforced effect at the end of the fiber.

Three dimensional(3D)displacements,which can be translated further into 3D strain,are key parameters for design,manufacturing and quality control.Using different optical setups,phase-shift methods,and algorithms,several different 3D electronic speckle pattern interferometry(ESPI)systems for displacement and strain measurements have been achieved and commercialized.This paper provides a review of the recent developments in ESPI systems for 3D displacement and strain measurement.After an overview of the fundamentals of ESPI theory,temporal phase-shift,and spatial phase-shift techniques,3D deformation measurements by the temporal phase-shift ESPI system,which is suited well for static measurement,and by the spatial phase-shift ESPI system,which is particularly useful for dynamic measurement,are discussed.For each method,the basic theory,a brief derivation and different optical layouts are presented.The state of art application,potential and limitation of the ESPI systems are shown and demonstrated.

Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail.Many studies of wheel-rail frictional heating have been devoted to the temperature field,but few literatures focus on wheel-rail thermal stress caused by frictional heating.However,the wheel-rail creepage is one of important influencing factors of the thermal stress.In this paper,a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method.The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration.The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail.The effect of the creepage on the temperature rise,thermal strain,residual stress and residual strain under wheel-rail sliding-rolling contact are investigated.The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact.Both the temperature and thermal strain of rail increase with increasing creepage.The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile.When the creepage is large,the frictional heat has a significant influence on the residual stresses and residual strains of rail.This paper develops a thermo-mechanical coupling model of wheel-rail rolling-sliding contact,and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.

目的 探讨常规超声按照乳腺影像报告及数据系统(BI-RADS)标准与超声弹性应变率比值法对触诊阴性乳腺肿块的诊断价值.方法 常规超声检查按照BI-RADS-US标准将85例患者91个触诊阴性乳腺病灶进行分级,并于穿刺活检或手术切除前进行超声弹性应变率比值法测定.以病理诊断为金标准,构建受试者应用工作特征曲线( ROC),比较2种不同方法的诊断价值.结果 触诊阴性乳腺恶性病灶弹性应变率比值远大于良性病灶(分别为6.92±5.91和2.49±3.26),两者比较差异显著(P<0.01);弹性应变率比值法与BI RADS-US标准的曲线下面积(AUC)分别为0.891和0.818.两者比较差异无统计学意义(P>0.05);2种方法联合应用构建ROC曲线AUC为0.976,与BI-RADS-US标准比较差异有统计学意义(P<0.01),与弹性应变率比值法比较差异有统计学意义(P<0.05).结论 弹性应变率比值法对触诊阴性乳腺病灶的良恶性评估价值明显;常规超声与超声弹性成像联合应用有助于判断触诊阴性乳腺病灶的良恶性,具有重要的临床应用价值.

目的 应用二维应变技术(2 DS)分析双腔起搏器置入前、后左室局部心肌的应变特点.方法 应用二维应变软件测量33例置入双腔起搏器患者术前、后的心尖四腔长轴左室壁各个节段的心肌纵向收缩期峰值应变(S)与应变率(SR).结果 与术前比较,双腔起搏器患者术后的后间隔中间段及心尖段、侧壁中间段及心尖段的心肌纵向收缩期峰值应变(S)与应变率(SR)均明显升高,差异均具有统计学意义(P均<0.05);其余左室壁节段置入双腔起搏器前、后的应变(S)与应变率(SR)差异均无统计学意义(P均>0.05).结论 置入双腔起搏器后,左室壁各节段心肌纵向运动的形变能力是不完全一致的.

利用第一性原理计算方法密度泛函理论的局域密度近似计算了纤锌矿氮化铝(AlN)、氮化镓(GaN)、氮化铟(InN)及其合金在双轴应变下的电子有效质量.对于GaN和AlN,张应变使电子有效质量增大而压应变使电子有效质量减少,但却使InN电子有效质量在张应变和压应变下都增大.由于三元合金(AlxGa1-xNx InxGa1-xN和AlxIn1-xN)与GaN异质结的新颖特性,同时计算了三元合金在松弛和应变下电子有效质量的变化趋势.受制于GaN基板的平面应力,外延AlxGa1-xN和AlxIn1-xN电子有效质量将减少,而InxGa1-xN电子有效质量增大,且随着In含量变大而更显著.对铟氮化合物应变下电子有效质量异常的机制也做了讨论.

基于沥青路面裂纹扩展行为,设计预切口小梁试件的疲劳试验,以模拟其复合裂纹扩展模式;以疲劳寿命指标来评价沥青混合料的抗裂性能,同时进行沥青混合料的低温弯曲试验和J积分试验,试验混合料采用4种低温性能差异显著的沥青胶结料.判别各项评价指标对试验混合料抗裂性能的鉴别程度,并分析沥青低温临界温度指标、低温弯曲试验指标、J积分试验指标与预切口小梁疲劳寿命的相关性.结果表明:以混合料疲劳性能为基准的混合料抗裂性能排序与沥青胶结料临界温度的排序一致,也与沥青混合料低温弯曲试验和J积分试验中能量指标的排序一致.