Background

Nowadays there is no currently accepted test specimen to measure the mode III fracture toughness of rigid monolithic and composite materials.

Objective

To propose and evaluate a new and simple test specimen called the Transverse Shear Cracked Plate to characterize the mode III fracture toughness of an epoxy resin.

Methods

The proposed specimen consists of a cantilever 38 mm × 38 mm square plate with a centered crack subjected to a transverse deflection. Specimens with two thicknesses (2.5 and 4 mm) and six crack lengths were tested, \(72\) in total. Finite element analysis was performed to calculate the energy release rates.

Results

A linear force–displacement behavior was commonly observed prior to fracture. The crack extension was typically longitudinal, uniform and unstable, splitting the specimen in halves. Radial patterns of prominent twist hackles that tend to curve toward outside the fracture origin were observed in the fractured surfaces and river markings appeared near one specimen edge as indication of mixed mode I/III loading. Analysis of the energy release rates showed a dominant parabolic-like mode III component along the crack front, although minor mode I and II components appeared near the edges.

Conclusions

Except for two cases that exhibited fragmentation, there is no apparent effect of the crack length on the fracture toughness, averaging 2.04 and 2.15 kJ/m² for 2.5 mm and 4 mm thick samples. Based on the simulations and measurements, the proposed test specimen is suitable to measure mode III fracture toughness.

中文翻译：

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使用横向剪切裂纹板试样的模式 III 断裂韧性测量

背景

目前还没有公认的测试样品来测量刚性整体材料和复合材料的 III 型断裂韧性。

客观的

提出并评估一种称为横向剪切裂纹板的新型简单试样，以表征环氧树脂的 III 型断裂韧性。

方法

建议的试样由一个悬臂 38 mm × 38 mm 方形板组成，带有一个受横向偏转的中心裂纹。测试了两种厚度（2.5 和 4 毫米）和六个裂纹长度的试样，总共\(72\)。进行有限元分析以计算能量释放率。

结果

在断裂之前通常观察到线性力-位移行为。裂纹扩展通常是纵向的、均匀的和不稳定的，将试样分成两半。在断裂表面观察到倾向于向断裂起点外弯曲的突出扭曲裂纹的径向图案，并且在一个试样边缘附近出现河流标记，作为混合模式 I/III 加载的指示。能量释放率的分析表明，沿裂纹前沿主要是抛物线状的 III 型分量，尽管在边缘附近出现了次要的 I 型和 II 型分量。

结论

除了出现碎裂的两种情况外，裂纹长度对断裂韧性没有明显影响，2.5 mm 和 4 mm 厚的样品平均为 2.04 和 2.15 kJ/m ²。基于模拟和测量，所提出的试样适用于测量 III 型断裂韧性。