| DU Yu,LIU Chang,YUAN Wen-hui.Effect of Delamination Damage on Tensile Properties and Surface Strain of Open-hole CF/PEEK Composites[J],52(7):239-249 |
| Effect of Delamination Damage on Tensile Properties and Surface Strain of Open-hole CF/PEEK Composites |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.07.021 |
| KeyWord:CF/PEEK composite drilled hole damages tensile properties digital image correlation surface strain |
| Author | Institution |
| DU Yu |
School of Mechanical Engineering, Tiangong University, Tianjin , China;Engineering Research Center of Integration and Application of Digital Learning Technology, Ministry of Education, Beijing , China |
| LIU Chang |
School of Mechanical Engineering, Tiangong University, Tianjin , China |
| YUAN Wen-hui |
School of Mechanical Engineering, Tiangong University, Tianjin , China |
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| Abstract: |
| The work aims to investigate the correlation between delamination damage on drilled hole surface and surface strain distribution of open-hole CF/PEEK composites under tensile load. Drilling experiments were carried out on CF/PEEK composite laminates with twist drill. The effects of different feed speed on the drilling temperature, drilling thrust force, surface delamination of the drilled hole outlet and the surface damage of the hole wall were analyzed. The effects of delamination damage on the tensile properties and surface strain distribution of open-hole CF/PEEK composite laminates were investigated through the combination of digital image correlation (DIC) and tensile experiments. The fracture morphology of the specimens was observed by scanning electron microscope, and the failure mode of the open-hole specimens under tensile load was analyzed. With the increase of feed speed, the time used to drill the workpiece was shorter, the accumulation of cutting heat was reduced, and the drilling temperature was reduced. Lower feed speed led to higher drilling temperature and softer matrix, and lower feed speed could produce relatively lower drilling thrust force. The increase of the feed speed led to the increase of the drilling thrust force, which aggravated the delamination damage of the outlet surface. The cutting surface of each specimen was coated with resin and the hole wall showed delamination, crack, fiber pull out and fiber debonding. As the degree of delamination damage increased, the tensile strength of the laminates tended to decrease and the tensile strength of the specimen was reduced from 558.4 MPa to 525.63 MPa, with a reduction of 5.87%. The maximum negative strain in the x-direction of the specimen increased with the degree of delamination damage under middle and high stress states. It could be seen that the maximum negative strain exhibited sensitivity to the degree of delamination damage under middle and high stress states. The maximum positive strain in the y-direction of the specimen increased with the degree of delamination damage under high stress state. It could be seen that the maximum positive strain exhibited sensitivity to the degree of delamination damage under high stress states. At the macroscopic scale, the fracture mode of matrix cracking, fiber splitting and delamination were mainly observed which was mainly due to fiber breakage after drilling process and the strength of the fiber-matrix interface was poor. With the increasing tensile load, the crack/damage areas began to extend along the fiber direction. The specimen exhibited brittle failure on a macroscopic scale. At the microscopic scale, the transverse fiber was perpendicular to the load direction, and the failure mode of the fiber was shear slip. Fiber debonding and shedding were observed. The longitudinal fiber was consistent with the direction of the load and the failure mode of the fiber was tensile failure. The fracture was characterized by fiber pull-out and unbroken fiber. Delamination damage on the drilled hole surface reduces the tensile strength of CF/PEEK composites. The surface strain distribution of open-hole CF/PEEK composite laminates with different delamination damage degrees shows obvious differences. The research results can provide a reference for the optimization of CF/PEEK composite laminates drilling process. |
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