Background

The effect of loading rate on the fracture properties of materials had been the subject of interest for more than four decades. However, the effect of loading rates on Mixed-mode fracture, involving Modes I and III, is known little due to the complexity of loading conditions and the inertia effect at a high loading rate.

Objective

The main objective is to develop a framework to investigate the relationship between loading rate and fracture parameter under Mixed-mode (I/III) loading conditions using a novel laboratory setup.

Methods

Experimentally, a modified spiral Notched specimen, stereo-digital image correlation, and a torsional Hopkinson bar apparatus are employed to characterize the dynamic fracture response of materials subjected to a combined torsion and tension loading. Specimens with different gauge lengths were used to generate low, intermediate, and high loading rates associated with Mixed-mode (I/III) notch tip conditions. Numerically, finite element analyses were performed to calculate the dynamic stress intensity factor using the dynamic interaction integral approach.

Results

The fracture initiation time was seen to be related to the spiral angle. It was found that the Mixed-mode fracture initiation toughness increase with the loading rate. For Aluminum 2024-T3, the dynamic fracture initiation toughness under Mode-III is threefold smaller than the Mode-I condition.

Conclusions

The proposed approach, dynamic tension–torsion loading of a spirally notched specimen, successfully generates a range of loading rates on Mixed-mode fracture involving Modes I and III conditions. The dynamic integral method was effectively used to extract fracture parameters at different loading rates and conditions. Therefore, the proposed approach is a promising method for investigating the dynamic Mixed-mode fracture of materials involving Mode I and III conditions.

中文翻译：

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发生混合模式 I/III 断裂的缺陷的加载速率效应

背景

四十年来，加载速率对材料断裂性能的影响一直是人们感兴趣的主题。然而，由于加载条件的复杂性和高加载速率下的惯性效应，加载速率对混合模式断裂（包括模式 I 和 III）的影响知之甚少。

客观的

主要目标是开发一个框架，以使用新型实验室设置研究混合模式 (I/III) 加载条件下加载速率与断裂参数之间的关系。

方法

实验上，采用改进的螺旋缺口试样、立体数字图像相关和扭转霍普金森杆装置来表征材料在组合扭转和拉伸载荷下的动态断裂响应。具有不同标距长度的样品用于产生与混合模式 (I/III) 凹口尖端条件相关的低、中和高加载率。在数值上，进行有限元分析以使用动态相互作用积分方法计算动态应力强度因子。

结果

断裂起始时间被认为与螺旋角有关。发现混合模式断裂起始韧性随着加载速率的增加而增加。对于铝 2024-T3，模式 III 下的动态断裂起始韧性比模式 I 条件小三倍。

结论

所提出的方法，即螺旋缺口试样的动态拉伸扭转加载，成功地在涉及模式 I 和 III 条件的混合模式断裂上产生了一系列加载速率。动态积分法有效地用于提取不同加载速率和条件下的裂缝参数。因此，所提出的方法是研究涉及模式 I 和 III 条件的材料的动态混合模式断裂的有前途的方法。