The effect of hole‐making process on the performance of CFRP/Ti multi‐bolt joints and load distribution

Abstract The CFRP/Ti multi‐bolt joints are commonly used in important structural parts of aircraft. These structure often adopts an integrated drilling method to improve manufacturing efficiency and avoid assembly problems. However, significant differences in material properties between CFRP and titanium alloy can affect hole accuracy, leading to deviations in hole‐size that impact joint performance. In response to these challenges, this study conducted experiments on the hole‐making process for CFRP/Ti laminated multi‐bolt joints and analyzed hole‐size characteristics and precision. The research investigated the effect of hole‐making processes on the static tensile and fatigue performance of CFRP/Ti three‐bolt single‐lap joints specimens and revealed the influence of hole‐size characteristics on load distribution among bolts. Results indicated that titanium alloy chip formation during CFRP hole drilling induced a microcutting effect on CFRP hole walls, resulting in stepped holes. The use of low‐frequency vibration‐assisted drilling improved chip removal and enhanced hole‐making precision. The use of the LDR‐LDR‐CD combined hole‐making process can mitigate the secondary bending phenomenon of critical bolt in CFRP/Ti three‐bolt, single‐lap joints specimens, thereby reducing local stress concentrations. This process combination effectively distributes bolt loads evenly, resulting in a reduction of the bolt load ratio in critical holes by 6.2%, and increases ultimate load and fatigue life by 6.7% and 47.7%, respectively. Therefore, in the hole‐making process of CFRP/Ti multi‐bolt joints, it is crucial to ensure that the precision of critical holes is lower than that of auxiliary holes to decrease the bolt load ratio in critical holes and enhance structural joint performance. Highlights Novel method for uniformly distributing load based on controlling drilling precision. The formation process of CFRP/Ti hole diameter characteristics in different processes. The LDR‐LDR‐CD can optimize load distribution, improve ultimate load and fatigue life.