Evolution Law of Deformation Field of Short Crack Tip under High-Frequency Resonant Loading Using a Microscope DIC System

doi:10.12382/bgxb.2022.0153

Abstract

Abstract:

To study the propagation mechanism of short fatigue cracks, a method is proposed to measure the displacement field, strain field, and plastic zone of the short crack tip of plastic metal materials under high-frequency resonant loading using microscope Digital Image Correlation (micro-DIC). And the evolution law of the displacement field, strain field, and plastic zone are studied. First, short crack images of the specimen under maximum resonant loading during fatigue crack growth (FCG) are collected by a microscope camera system. Second, data of the displacement field and strain field at the crack tip region are obtained using the DIC method. Third, the coordinates of the crack tip during short crack propagation are obtained by the virtual extensometer along with the displacement field evolution data. Then, based on the von Mises yield criterion and strain field data, evolution law of the size of the plastic zone is studied and compared with the Irwin model. Last, grain size distribution on the crack tip of 316 stainless steel, a typical plastic metal material, is measured by EBSD technology. The evolution law of displacement and strain along the grain scale in the short crack tip region under high-frequency resonant loading is further studied. The research results show that the proposed method can successfully obtain the micron-scale deformation field evolution data of short cracks, providing experimental and theoretical support for further examination of short fatigue cracks and fatigue life prediction of plastic metal materials under high-frequency resonant loading.

Key words: resonant fatigue growth, micro-DIC, short crack, deformation field, plastic zone, evolution

SHAN Xiaofeng, GAO Hongli, HUANG Xinwei, LIN Zhiyuan, SHANG Hongbin. Evolution Law of Deformation Field of Short Crack Tip under High-Frequency Resonant Loading Using a Microscope DIC System[J]. Acta Armamentarii, 2023, 44(5): 1482-1492.

Figures/Tables 21

Fig.1 Dimensions of a CT specimen

Fig.2 Dimensions of a dog-bone shaped specimen

Table 1 Material parameters of 316 stainless steel

弹性模量/GPa	泊松比	屈服强度/MPa
195	0.3	335

Fig.3 Orientation distribution of stainless steel 316

Fig.4 Micro-image acquisition system of resonant fatigue short cracks

Table 2 Main hardware parameters

硬件	型号	主要参数
相机	acA4112-30μm	分辨率:4096(H)×3000(V) 靶面尺寸:1.1″ 最大帧率:30帧/s 最短曝光时间:2μs 像元尺寸:3.45μm×3.45μm
镜头	Rodagon 5.6/105metal	焦距:105mm 最大成像圆直径:102mm 工作距离:292~1853mm

Fig.5 Schematic diagram of DIC

Fig.6 Setup of thevirtual extensometer

Fig.7 Schematic diagram of fitting curve derivation

Fig.8 Equivalent strain field and plastic zone distribution at the crack tip

Fig.9 Micro-image acquisition system for capturing short fatigue cracks under resonant loading

Fig.10 Prepared speckle specimen

Fig.11 Crack images under different fatigue cycles

Fig.12 Vertical displacement nephogram

Fig.13 Extensometer tensor curves at different positions

Fig.14 Displacement curve at different positions of the vertical line of the crack tip

Fig.15 Estimation of plastic zone at the crack tip

Fig.16 Crack-tip plastic zone in the equivalent strain field

Fig.17 Layout of measuring points near the crack tip

Fig.18 Displacement curves at measuring points

Fig.19 Equivalent strain curves at measuring points

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