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首页> 外文期刊>Journal of Composite Materials >Influences of friction, geometric nonlinearities, and fixture compliance on experimentally observed toughnesses from three and four-point bend end-notched flexure tests
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Influences of friction, geometric nonlinearities, and fixture compliance on experimentally observed toughnesses from three and four-point bend end-notched flexure tests

机译：摩擦，几何非线性和固定装置的柔韧性对三点和四点弯曲端切口挠曲测试中实验观察到的韧性的影响

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Three and four-point bend end-notched flexure tests, comprising a number of different test geometries, are performed on two different graphite/epoxy composites, and the toughnesses are obtained by a compliance calibration method of data reduction. The coefficient of friction along the crack plane and the flexural modulus of each material are then determined experimentally and used with nonlinear finite-element analyses to simulate these same test configurations. By using the mean experimentally observed critical load, these simulations are used to obtain the materials' toughnesses by three different methods. The first uses a previously developed 'direct energy balance approach,' which is assumed to produce the 'true' toughness. The second is by a simulated compliance calibration procedure, which is used to obtain the perceived toughness for an infinitely stiff fixture. In the third approach, experimentally determined fixture compliances, as a function of the test geometry, specimen, and crack length, are used along with the simulated compliance calibration procedure to obtain a perceived toughness that accurately accounts for the effects of friction, geometric nonlinearities, and fixture, compliance. The perceived toughnesses as obtained by these simulations are shown to accurately recreate the perceived values of toughness that are obtained from the physical tests. Moreover, the finite-element simulations indicate that the true toughness values are essentially constant for a given material, and that the three-point bend end-notched flexure test will provide perceived toughnesses that correspond quite closely to the true value, whereas the four-point bend test often will not. For these reasons, the three-point bend configuration was found to be the more preferable of the two tests.
机译：在两种不同的石墨/环氧树脂复合材料上进行了包括许多不同测试几何形状的三点和四点弯曲的末端切口挠曲测试，并通过数据缩减的顺应性校准方法获得了韧性。然后通过实验确定沿着裂纹平面的摩擦系数和每种材料的弯曲模量，并将其与非线性有限元分析一起使用，以模拟这些相同的测试配置。通过使用实验观察到的平均临界载荷，这些模拟可通过三种不同的方法来获得材料的韧性。第一种使用以前开发的“直接能量平衡方法”，假定产生“真实”的韧性。第二种是通过模拟的柔度校准程序，该程序用于获得无限刚性夹具的感知韧性。在第三种方法中，根据测试几何形状，试样和裂纹长度，通过实验确定的夹具柔度与模拟的柔度校准程序一起使用，以获得可感知的韧性，可以准确地说明摩擦，几何非线性，和固定装置，合规性。通过这些模拟获得的感知韧性被显示为准确地重现了从物理测试获得的韧性感知值。此外，有限元模拟表明，对于给定的材料，真实的韧性值基本上是恒定的，并且三点弯曲的末端切口挠曲测试将提供与真实值非常接近的可感知的韧性，而四点-点弯曲测试通常不会。由于这些原因，发现在两个测试中三点弯曲配置更为可取。

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