Effects of constitutive parameters on the accuracy of measured fracture energy using the DCB-specimen

Several methods exist to estimate the fracture energy for adhesive joints using the double cantilever beam specimen and linear elastic fracture mechanics. Since the mechanical properties of all adhesives are non-linear, errors are generated. By use of an exact solution experiments are simulated. These are evaluated with eight different methods. The influence of the constitutive parameters is systematically studied. This influence is small for most methods. The error due to the choice of evaluation method is considerably larger. One of the commonly used methods gives accurate results; the error is less than 3%. However, most methods yield substantial errors.     

用开缺口冲击标样校验冲击机的必要性和有效性--全国冲击试验能力验证结果分析

叙述了发达国家和国际标准化组织对冲击试验机校验及对校验用冲击标样的要求,指出发达国家采用高度纯净和均匀的40CrNiMo钢制作开缺口的冲击标样,成本高,限制了发展中国家大量采用这种标样.提出并用热轧低碳钢板研制成开缺口内控冲击标样,变异系数<3%,且成本低廉,在实际应用中,特别是在2001年中国实验室能力验证委员会组织的冲击试验能力验证工作中,这种试样对于验证冲击机的精度是有效的,证明定期采用开缺口冲击标样校验冲击机是必要的.同时提出,为了有效校验冲击机的精度,至少必须采用一组数量不少于两只冲击功预期值相同的冲击标样.     

内蒙古大兴安岭根河植被覆盖度动态变化及影响因素的分析

研究植被覆盖度（Fractional Vegetation Cover,FVC）动态变化,可增强了解森林群落的抵抗力和恢复力,为森林生态系统定量评价提供科学依据。基于像元二分模型、Landsat-5 TM（2006、2010）及高分一号（GF-1,2016）数据估算了3个时期的根河市FVC,引入变化率和动态度2个指标评价其动态变化情况,并且分析了多因素对该变化的影响。实验结果显示：中度以上等级占总面积80%以上,2016年低、较低、中度、较高、高等级FVC分别为1 645.02、1 655.97、3 536.59、5 556.87、7507.15 km²。采用0.2 m航空CCD影像进行植被/非植被点提取后,针对2016年的FVC估算结果进行交叉验证的精度为0.92。变化分析结果显示：除部分地区外（敖鲁古雅）,2006~2016 年间FVC变化整体上呈增加态,尤其是高等级增加了1 668.78 km²。综合来看,根河市植被覆盖良好,多重因素共同影响其动态变化,局部FVC对火灾干扰的变化极为敏感,低海拔和平坡FVC明显降低,与人类生产生活密切相关。     

Impact stabilizing controller for hydraulic actuators with friction: Theory and experiments

Stabilizing manipulators during the transition from free to constraint motion is an important issue in contact task control design. This paper documents the development, theoretical analysis and experimental evaluation of a Lyapunov-based control scheme to regulate the impacts of a hydraulic actuator that comes in contact with a nonmoving environment. Upon sensing a nonzero force, the controller positions the actuator at the location where the force was first sensed, exerting minimal force on the environment. The scheme does not require continuous measurement of force or velocity during the short period of impacts, making it very useful for practical cases. Furthermore, no knowledge of the impact dynamics, friction effects, servovalve dynamics, or hydraulic parameters is required for control action. Stability of the control scheme is verified via analytical analyses. Due to the discontinuous friction model and the discontinuous nature of the proposed control law, the control system is nonsmooth. The existence, continuation and uniqueness of Filippov's solution to the system are, therefore, investigated. The extension of LaSalle's invariance principle to nonsmooth systems is next employed to prove that all the solution trajectories converge to the equilibria. The controller is finally tested experimentally to verify its practicality and effectiveness in collisions with hard and soft environments and with various approach velocities.     

中国传统文化对于殡葬产品设计的影响

本文从中国传统殡葬观念出发(民族殡葬文化不包含在内),探究了传统与现代相结合的殡葬用品的时代特点,并在我国提倡"绿色殡葬"理念的背景下,结合了世界其他国家的当代殡葬用品发展,分析了中国传统文化对于殡葬产品设计的影响。     

垂直冲击试验机的研制

为满足简便检测塑料产品抗冲击强度的需求,研制了垂直冲击试验机。对垂直冲击试验机的结构进行了设计,基于力学原理进行了受力计算,并对工作原理与相对基准设定问题进行了分析。介绍了垂直冲击试验机的操作方法,并进行了规格校验。     

三种疲劳蠕变交互作用寿命预测模型的比较及其应用

对疲劳蠕变交互作用寿命预测方法进行简单回顾,并分别介绍从能量耗竭、韧性耗竭、延性耗竭角度提出的三种应力控制疲劳蠕变寿命预测方法.通过文献试验数据和1.25Cr0.5Mo钢520℃应力控制、梯形波加载试验数据对上述三种模型的优缺点和适用范围进行评价.三种方法的预测精度都大大高于传统的频率分离法和应变能频率分离法;能量模型对应力应变控制模式都适用,延性耗竭模型预测精度最高,平均应变速率模型形式最简单,适用于应力控制下纯蠕变、纯疲劳或疲劳蠕变交互作用下的各种失效组合模式,拓宽了Monkman-Grant经验关系式的应用范围,因此具有重要的工程应用价值和应用前景.最后阐述平均应变速率模型的应用步骤.     

X60钢级管线钢焊接热影响区的热模拟研究

采用焊接热模拟技术对X60钢级管线钢进行了热影响区模拟试验。研究了该钢在不同的峰值温度和冷却时间下的韧性和组织,测定了其热影响区的硬度。结果表明,峰值温度越高X60钢级管线钢的组织越粗大、韧性越低;在不同的峰值温度下,冷却时间对该钢焊接热影响区组织及韧性的影响是不同的。     

Prediction of mode I fracture toughness of rock using linear multiple regression and gene expression programming

Prediction of mode I fracture toughness(KIC) of rock is of significant importance in rock engineering analyses. In this study, linear multiple regression(LMR) and gene expression programming(GEP)methods were used to provide a reliable relationship to determine mode I fracture toughness of rock. The presented model was developed based on 60 datasets taken from the previous literature. To predict fracture parameters, three mechanical parameters of rock mass including uniaxial compressive strength(...     

爆炸冲击波在巷道内的传播规律

爆炸冲击波在巷道内的传播规律,一直是采矿科学中的重要课题。由巷道现场的测试结果可以看出:随着测点与爆源距离的增大,二次爆炸冲击波与首次波的压力比不断地增加,在一定情况下,其比值可大于1,同时二次波与一次波的峰值间隔在不断地缩小,波的正压力时间加长。小药量的实验结果在一定的程度上也较能真实地反映实际爆炸作业时的情况。