Citation: Wang, H.; Zhang, X.; Duan,
Y. Investigating the Effect of
Low-Temperature Drilling Process on
the Mechanical Behavior of CFRP.
Polymers 2022, 14, 1034. https://
doi.org/10.3390/polym14051034
Academic Editors: Alberto
Campagnolo and Alberto Sapora
Received: 12 February 2022
Accepted: 1 March 2022
Published: 4 March 2022
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Article
Investigating the Effect of Low-Temperature Drilling Process on
the Mechanical Behavior of CFRP
Hongxiao Wang
1,2,3
, Xiaohui Zhang
2,
* and Yugang Duan
2
1
School of Mechanical and Electrical Engineering, Henan University of Technology, No.100 Lianhua Road,
Gaoxin District, Zhengzhou 450001, China; zzwhx2019@haut.edu.cn
2
State Key Lab for Manufacturing Systems Engineering, School of Mechanical Engineering,
Xi’an Jiaotong University, No.99 Yanxiang Road, Xi’an 710054, China; ygduan@xjtu.edu.cn
3
Henan Weihua Heavy Machinery Co., Ltd., No.18 Shanhai Road, Changyuan 453400, China
* Correspondence: zhangxiaohui@xjtu.edu.cn
Abstract:
Previous research has found that lower temperature drilling is helpful to improve the hole
quality of carbon fiber reinforced polymer (CFRP). However, the influence of the lower temperature
drilling process on the mechanical behavior of composites is yet not fully understood. To examine
the influence of the lower temperature drilling process on the mechanical behavior of CFRP, the
open hole CFRP specimens used for mechanical tests were obtained with three cases: drilling with
−25
◦
C
/uncoated carbide drills/(1000 rpm, 0.02 mm/r), 23
◦
C/coated carbide drills/(4000 rpm,
0.03 mm/r), and 23
◦
C/uncoated carbide drills/(1000 rpm, 0.02 mm/r), respectively; corresponding,
three groups of open-hole specimens are obtained: specimens drilling at low-temperature with
low damage, specimens drilling at room-temperature with low damage and specimens drilling at
room-temperature with low damage; the mechanical behavior of the three groups specimens were
obtained by static tensile, tensile–tensile fatigue cyclic tests and residual tensile strength test. The
results have shown that the mechanical properties of specimens with a low-temperature drilling
process is lower than those of the specimen with a normal drilling process due to the better drilling
quality. The damage accumulation in specimens was increased with the damage degree of the original
hole, the greater the damage degree, the worse the mechanical properties.
Keywords:
lower temperature drilling process; mechanical behavior of CFRP; damage accumulation;
static tensile tests; fatigue cyclic tests
1. Introduction
Carbon fiber reinforced polymer (CFRP) materials are being widely used in aerospace,
automotive and marine industries because of their high stiffness-to-weight and strength-to-
weight ratios [
1
], strong design ability [
2
], good fatigue [
3
], and corrosion performance [
4
,
5
].
Although additive manufacturing is usually used to produce carbon fiber composite parts
in the industry, its link parts need to be machined [
6
]. Drilling is a frequent machining
process in the industry due to the need for component assembly [
7
]. However, due to the
poor thermal conductivity of CFRP, the drilling area’s temperature is always far higher than
the glass transition temperature of the resin matrix [
8
–
10
], causing drilling delamination,
splitting, burr and other damage. According to refs. [
11
], when drilling area temperatures
are higher than the glass transition temperature of the resin matrix, the interfacial shear
strength of CFRP sharply decreases leading to large defects in the drilled hole surface.
Meanwhile, the delamination is easily produced with the matrix degradation under the
high drilling temperature.
To improve the drilling quality, cryogenic machining is used for machining CFRP
and has made certain achievements in recent years [
12
–
14
]. For example, Bhattacharyya
et al. [
15
] investigated the drilling process of composites under cryogenic conditions and
reported that drilling quality was improved by cryogenic cooling. Xia et al. [
16
] investigated
Polymers 2022, 14, 1034. https://doi.org/10.3390/polym14051034 https://www.mdpi.com/journal/polymers
