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案例“:长方形、正方形面积的计算”教学片段。1.引导猜测。师:我们已经知道,长方形的周长与它的长、宽有关。那么,长方形的面积与什么有关呢?生1:长方形的面积也与它的长、宽有关。生2:长方形的面积与它的周长有关。……师:是吗?我们一起来看一看。(教师在钉子板上用橡皮筋直观演示验证:把长方形的长(或宽)拉长,长方形的面积也变大。使学生确信:长方形的面积和它的长与宽有关,也与它的周长有关。)2.分组操作。师:那么,长方形的面积究竟和它的长与宽有什么关系呢?请各学习小组一起动手,从各组准备的25个1平方厘米的正方形中选出任意几个拼成… 相似文献
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郑建英 《小学教学(数学版)》2014,(6):38-38
前不久．我执教了一节送教下乡课“长方形、正方形面积的计算”。课中。孩子们很快提出“我想知道长方形的面积与长方形的什么有关”的问题．并根据已有的知识经验进行积极的猜想。他们认为：“长方形的面积可能与长方形的长和宽有关系。”随后在钉子板上进行验证,并通过对几个已知长和宽的长方形面积的研究,孩子们发现这几个长方形的面积都等于长×宽。 相似文献
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本文通过对WE-600A型液压万能试验机液压夹紧活塞杆破坏的原因分析,认为破坏是因杆在交变应力作用下,由偏心压缩引起的弯曲正应力与压缩产生的正应力叠加;以及应力集中造成的.针对破坏原因,对活塞杆、推拉板作了改进,效果显著. 相似文献
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为了揭示十字板焊接空心球节点(简称板球节点)常幅疲劳破坏机理并建立其相应计算公式,对板球节点进行疲劳试验.基于自行设计的加载装置,进行了19个节点试件的常幅疲劳试验;采用有限元对节点进行静力分析,并利用扫描电子显微镜对节点疲劳破坏断口进行金相分析.数值模拟和试验结果表明:板球节点中热点位于连接焊缝焊址球面处,且该点应力集中程度严重;节点疲劳裂纹萌生于焊缝焊址处且以板宽为直径沿球面环向扩展直至疲劳断裂.节点初始焊接缺陷及构造细节是构成疲劳失效的主要因素.基于常幅疲劳试验结果线性拟合得到了该节点的S-N曲线,并以热点应力幅为变量建立了其常幅疲劳计算公式. 相似文献
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李冬梅 《广东教育学院学报》2007,27(3):56-58
为了揭示多个表面割口单向纤维增强复合材料叠层板的拉伸破坏机理,预估其破坏规律,基于剪滞理论,建立一种对各单层分划为有限子单元的剪滞分析模型,分析含三个平行的表面割口单向叠层板在拉伸载荷作用下的应力重新分布及各割口之间的相互影响问题,获得了表面割口附近完整纤维的应力集中因子、应力及位移分布规律. 相似文献
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赵宝光 《聪明泉(少儿版)》2004,(1)
<正> 下面给同学们介诏一下移板游戏。做:用厚纸剪出一个长8厘米宽6厘米的矩形板(图一)。用厚纸再剪出一个长8厘米宽6厘米的矩形板,然后在其中间挖掉一个长6厘米宽4厘米的矩形,得出一个 相似文献
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电容器是电器设备中非常重要的元件之一,也是非常普遍的元件,它广泛运用于电子技术与电工技术中.平行板电容器是一种最简单的电容器,在近年高考中,有关平行板电容器的问题频频出现,也由此可看出它在高中物理中的重要性.所以,在物理复习中,教师要注意引导学生理解、掌握平行板电容器的知识,提高学生在平行板电容学习中的分析问题、解决问题的能力.本文结合近几年高考试题中出现的与平行板电容器有关的试题进行归纳总结,供师生参考. 相似文献
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钟健生 《Journal of Zhangzhou Technical Institute》2012,14(2):32-36
以实际工程为例,对现浇楼板跨中产牛的温度收缩裂缝进行了调查研究,结合温度收缩应力计算、应力集中分析,从理论上验证板中预埋线管处应力的集中,引起局部温度收缩应力过大,诱发产生温度收缩裂缝的现象,为今后的楼板裂缝控制提供了有益的参考。 相似文献
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Finite element models were established to analyze the influence of soft filler on stress concentration for a rectangular plate with an elliptic hole in the center. The influence was quantified by means of stress concentration factor (SCF). Seven shape factors of the elliptic hole and three levels of elasticity modulus of the soft filler were considered. The reduction coefficient and sensitivity index of SCF are the two indicators in evaluating the influence of soft filler. It was found that the reduction coefficient of SCF increases significantly as the shape factor and the elasticity modulus of the filler increase, indicating that soft filler can reduce the concentrated stress effectively, especially when the shape factor is great. Analysis for the sensitivity index of SCF indicates that SCF is more sensitive to materials with small elasticity modulus than to materials with large one. 相似文献
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INTRODUCTION For moderate thickness plate containing notches or holes, neither plane stress nor plane strain theory can describe its true deformation states (Jin and Hwang, 1989). This well known drawback has mo- tivated many analytical and numerical studies carried out to determine the effect of plate thickness on the in-plane stress distribution. Pioneering work on the along depth stress components, i.e. the K-M gener- alized plane strain theory was proposed by Kane and Mindlin (1956)… 相似文献
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The finite deformation and stress analyses for a rectangular plate with a center void and center void and made of rubber with the Yeoh elastic strain energy function under uniaxial extension were studied in this paper.An approximation solution was botained from the minimum potential energy principle.The num,erical results for the growth of the cavitation and stresses along the edge of the cavitation were discussed.In addition,the stress concentration phenomenon was considered. 相似文献
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肖志余 《武汉工程职业技术学院学报》2010,22(4):11-14,34
建立中厚板轧制压力计算模型,选取不同的应力状态系数模型对轧制压力进行预报,分析应力状态系数模型对轧制力预报精度的影响。结果表明：应力状态系数模型对轧制压力预报精度存在影响,当轧制较厚板时影响较大;中厚板轧制时,相对其他应力状态系数模型,采用模型Ⅱ计算,精度相对稳定,误差相对较小。 相似文献
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刘海侠 《河北软件职业技术学院学报》2007,9(3):63-65
本文在弹塑性断裂双参数分析方法的基础上,导出了预测压力容器等重要工程结构断裂韧度CTOD要求的理论表达式.只要在实际结构服役条件下,材料断裂韧度高于该表达式要求的韧度值,就可防止结构的弹塑性断裂失效.同时,在该表达式中考虑了应力集中及焊接残余应力的影响,并表明断裂韧度要求随作用应力及板厚的增加而增加.最后给出了两个实例,以考核该理论表达式的实用性. 相似文献
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To analyze the effects of width and thickness of each composition element of mixed steel U-rib-stiffened plates on the welding residual stress distribution, the distribution of the U-rib and the plate residual stress was calculated using a simplified calculation method. The method involved welding the mixed steel U-rib-stiffened plates for a structure with different sizes and different strength ratios of U-rib to plate. Based on a welding residual stress numerical simulation method validated by the blind hole method test, the distribution law of the mixed steel U-rib stiffened plate was studied. The results showed that the change of plate width has little impact on the welding residual stress and that the ratio of the thicknesses of the plate to U-rib stiffeners, the thickness of the plate, and the thickness of the U-rib has a great influence on the distribution of the welding residual stress. The thickness of plate and steel strength also greatly influenced the distribution width of the residual tensile stress. While analyzing the compression capacity of U-rib-stiffened plates, the simplified distribution of welding residual stress was used. 相似文献
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研究了温度、NaCl浓度以及溶液的pH值等环境因素对WDH36NF油船货油舱内底板用钢腐蚀速率、腐蚀形貌的影响。结果表明:油船货油舱内底板用钢的腐蚀速率随温度升高而增加。NaCl浓度由5%增大到10%,内底板用钢的腐蚀速率随浓度增大而增加,NaCl浓度由10%增大到15%,内底板用钢的腐蚀速率减小。pH值由0.5增大到0.85,内底板用钢的腐蚀速率随pH值增大而增加,pH值由0.85增大到1.2,内底板用钢的腐蚀速率减小,并趋于平缓。 相似文献
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The analyses of finite deformation and stress for a hyperelastic rectangular plate with some voids under an uniaxial extension were conducted. The governing differential equations were given from the incompressibility condition of the material. The solution was approximately obtained from the minimum potential energy principle. The growth of voids was discussed. One can see that an initial central circular-cylinder void becomes an elliptic-cylinder void, but an initial non-centeral circular-cylinder void becomes an elliptic-like cylinder void and the center of void has a shift. The stress distributions along the edges of voids were given and the phenomenon of stress concentration was observed. The influences of the distribution manner and size of voids, as well as the distance between them on the growth of voids were analyzed. 相似文献
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采用MP-PIC (multi-phase particle in cell)方法模拟了三维多段气化炉（上部快速床,下部鼓泡床）多粒径煤粉的循环流化过程,研究了分布板不同进气方向对气化炉内颗粒分布的影响。结果表明:分布板开孔与水平方向夹角越大,物料进入快速床并形成流化状态越快,但对成形后的流化形态影响较小;分布板进气方向对分布板处的轴向颗粒浓度分布影响较大,对快速床内轴向颗粒浓度分布影响较小;随着分布板进气方向与水平夹角的减小,鼓泡床下部颗粒浓度增大,固相颗粒通量增大;分布板进气方向对旋风分离效率影响较小。因此,工程上可根据需要适当减小分布板进气方向与水平方向的夹角来增加分布板上部颗粒浓度分布。 相似文献