共查询到20条相似文献，搜索用时 218 毫秒
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在物理学中，一般主要讨论滑动摩擦力，滚动中的摩擦力讲座较少，在滚动中，由于情况不同，轮子与接触面间的摩擦力方向不同，作功也要具体分析。 相似文献
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“老师,我不想坐后面,因为我的视力下降,看不清板书,XX老师上课声音太小,我听不清,我想坐到前面去……”“老师,坐在前面我好不自在,老师好象总盯着我,我头都不敢抬,在老师的眼皮底下,我感到有压力,喘不过气来。老师,我不愿坐在前面,我想让自己的心情放松……”……每次安排座位后不久,总有学生在周记上反复表示对现在座位的不满,大谈自已座位的弊端,让我耳根难有清静。要知道排一次座位可真不容易,要考虑高矮,要考虑成绩,要考虑性格,还要考虑班干部的比例等等,真可谓是绞尽脑汁,费尽心机,牵一发而动全身。如何让学生安心座位而不言其他呢?… 相似文献
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针对现行使用的普物力学教材中圆柱体无滑滚动条件的应用范围进行了明确,并强调了无滑滚动条件标量方程中各量的符号。 相似文献
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谢华明 《数理天地(初中版)》2013,(11):25-25,27
几何图形可以沿着一条直线尢滑动地翻滚,也可以沿另一图形内部边缘无滑动翻滚,还可以沿另一个图形外部边缘无滑动翻滚．下面举例谈谈儿何图形沿着一条直线无滑动地翻滚问题． 相似文献
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为了提高高速货运列车转向架弹簧的耐疲劳性能,对两个炉号的棒状60Si2CrVAT弹簧钢用相同工艺热处理后,在MTS880材料试验机上进行了三点弯曲疲劳寿命对比试验,实验载荷采用阶梯式增加法;用扫描电镜对弹簧钢的疲劳断口和基体组织进行观察。疲劳实验结果表明,不同炉号的弹簧钢疲劳寿命相差很大。组织分析表明,疲劳寿命较低的弹簧钢中,淬火加热前存在颗粒状碳化物,奥氏体化时未溶入奥氏体而残留在淬火组织中,并在局部聚集,导致疲劳寿命降低。 相似文献
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Improving the Fatigue Performance of the Welded Joints of Ultra-Fine Grain Steel by Ultrasonic Peening 总被引：2，自引：0，他引：2
Contrast tests were carried out to study the fatigue performance of the butt joints treated by ultrasonic peening, aiming at the improvement of ultrasonic peening treatment(UPT) on welded joints of a new material. The material is a new generation of fine grain and high purity SS400 steel that has the same ingredients as the traditional low carbon steel. The specimens are in two different states:welded and ultrasonic peening conditions. The corresponding fatigue testing data were analyzed according to the regulation of the statistical method for fatigue life of the welded joints established by International Institute of Welding(IIW). Welding residual stress was considered in two different ways: the constant stress ratio R = 0.5 and the Ohta method. The nominalstress-number (σ-N) curves were corrected because of the different plate thickness compared to the standard and because there was no mismatch or angular deformation. The results indicated that: 1 ) Compared with the welded specimens, when the stress range was 200 MPa, the fatigue life of the SS400 steel specimens treated by ultrasonic peening is prolonged by over 58 times, and the fatigue strength FAT corresponding to 106 cycles is increased by about 66％; 2) As for the SS400 butt joint ( single side welding double sides molding) , after being treated by UPT, the nominal S-N curve (m = 10) of FAT 100 MPa(R =0.5) should be used for fatigue design. The standard S-N curves of FAT 100 MPa (R = 0.5, m = 10) could be used for fatigue design of the SS400 steel butt joints treated by ultrasonic peening. 相似文献
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根据工厂的实际水平情况实现生产设备与生产流程的优化匹配,在符合实际生产要求的情况下最大限度地降低生产成本。针对蒸汽锅炉过热汽温和压力对象较差的动态特性,基于PLC和触摸屏技术的GCr15SiMn轴承钢铸造温度与工艺控制系统,显著细化了GCr15SiMn轴承钢铸造后的显微组织,改善了GCr15SiMn轴承钢铸造后的力学性能和耐磨损性能,具有较好的工业应用价值。 相似文献
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滚动轴承最小油膜厚度的分析计算研究 总被引：1，自引：0，他引：1
滚动轴承最小油膜厚度的准确计算对于滚动轴承疲劳寿命的精确估算非常重要,考虑影响滚动轴承最小油膜厚度的参数并对其进行了研究,通过Matlab回归分析得出了在热弹流润滑条件下新的接触点处的滚动轴承最小油膜厚度计算公式,并对此公式进行了显著性检验,证明此公式在一定条件下是正确可行的。 相似文献
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In the proposed system for online inspection of steel balls, a diffuse illumination is developed to enhance defect appearances and produce high quality images. To fully view the entire sphere, a novel unfolding method is put forward based on geometrical analysis, which only requires one-dimensional movement of the balls and a pair of cameras to capture images from different directions. Moreover, a realtime inspection algorithm is customized to improve both accuracy and efficiency. The precision and recall of the sample set were 87.7% and 98%, respectively. The average time cost on image processing and analysis for a steel ball was 47 ms, and the total time cost was less than 200 ms plus the cost of image acquisition and balls’ movement. The system can sort 18 000 balls per hour with a spatial resolution higher than 0.01 mm. 相似文献
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针对内、外焊缝余高过大导致焊缝处应力集中,抵抗动载荷能力下降等影响焊管力学性能的问题,在充分分析焊缝滚压冷轧处理工作流程的基础上,以西门子S7—200PLC为系统核心,EasyView触摸屏为人机界面,提出能够自行调节滚压行程、滚压速度、回程速度、加减速和比例阀控制死区等设置的一整套电气控制方案,完成对小口径不锈钢焊管的内、外焊缝的滚压冷轧处理,解决了以往设备需要依赖进口或调试困难、故障率高、维修难的问题,提高了产品成材率和品质,满足了生产大型电站、锅炉换热器用小口径不锈钢焊接管的生产工艺要求。 相似文献
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Fatigue and fracture behavior of nickel-based superalloy Inconel 718 up to the very high cycle regime 总被引：2，自引：0，他引：2
Xian-feng Ma Zheng Duan Hui-ji Shi Ryosuke Murai Eiichi Yanagisawa 《浙江大学学报(A卷英文版)》2010,11(10):727-737
The fatigue and fracture behavior of nickel-based superalloy Inconel 718 was investigated up to the very high cycle regime under rotary bending tests at room temperature. It was found that this superalloy can still fracture after exceeding 107 cycles. Fractographic analysis revealed that there was a transition from fatigue crack initiation at multi-sites to single initiation with decreasing stress levels. The fracture surface can be divided into four areas according to the appearance, associated with fracture mechanics analysis of the corresponding stress intensity factors. The fracture mechanism dominant in each area was disclosed by scanning electron microscope examination and analyzed in comparison with those obtained from the crack growth tests. Subsequently, life prediction modeling was proposed by estimating the crack initiation and propagation stage respectively. It was found that Chan （2003）＇s model for initiation life and the Paris law for growth life can provide comparable predictions against the experimental life. 相似文献
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A significant temperature raise within hydrogen vehicle cylinder during the fast filling process will be observed, while the strength and fatigue life of the cylinder will dramatically decrease at high temperature. In order to evaluate the strength and fatigue of composite hydrogen storage vessel, a 70-MPa fatigue test system using hydrogen medium was set up. Experimental study on the fatigue of composite hydrogen storage vessels under real hydrogen environment was performed. The experimental results show that the ultimate strength and fatigue life both decreased obviously compared with the values under hydraulic fatigue test. Furthermore, fatigue property, failure behavior, and safe hydrogen charging/discharging working mode of onboard hydrogen storage vessels were obtained through the fatigue tests. 相似文献
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INTRODUCTION A number of experimental fatigue studies were conducted on plain concrete as well as on steel fibre reinforced concrete (SFRC) beams of different sizes under different loading conditions. Murdock and Kesler (1958) investigated the effect of stress ratio on the fatigue strength of plain concrete. Batson et al.(1972) reported fatigue strength of 74% and 83% of the first crack static flexural strength at 2 million cycles of complete reversed and not-reversed loads respectively… 相似文献
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Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be employed to analyze the influence of variable-amplitude fatigue both in the elastic and plastic ranges. To evaluate the effect of the strain ratio on G20Mn5QT cast steel, the fatigue tests of smooth specimens were carried out at the strain ratio of 0.1. The cyclic deformation and the relationships between the strain amplitude, the stress amplitude, the Smith, Watson and Topper(SWT)parameter and fatigue life were studied and compared with those at the strain ratio of -1. Compared with other methods, Basquin formula and Solonberg formula provide reliable and appropriate ranges of S-N curve and fatigue limit at different strain ratios respectively. The SWT parameter can be used to predict the fatigue life at other strain ratios accurately. 相似文献