Cold expansion technology of connection holes in aircraft structures:A review and prospect

As one kind of key anti-fatigue manufacture approaches with simplicity and effectiveness, the hole cold expansion technology satisfies the increasing needs for light weight and durability of aircraft structures.It can improve the fatigue life by several times at no additional weight conditions.The hole cold expansion technology has been widely used in manufacturing and repairing of both fighters and commercial aircraft, and has become a research hotspot in the strengthening technology.In recent years, hole cold expansion process methods, residual stress around expanded holes, the behavior of fatigue crack initiation and propagation, and fatigue lives after cold expansion are researched extensively through lots of experiments and finite element simulations.A review on the hole cold expansion technology research status in the last twenty years is presented in this paper.Via the analysis of the current characteristics and defects of the hole cold expansion technology, combined with the actual needs in design and manufacture of new-generation aircraft, development trends and novel research directions are presented for realizing precise and high-efficiency anti-fatigue manufacture.

Residual stress around rail bolt holes after cold-expansion

Focused on rail bolt hole cold-expansion, the theoretical prediction models and results of residual stress analysis on related Problems are summarized. And a stress analyzing method based on both of the strain measurement duringthe Process of cold expansion and elastoc-plastic theory is developed. By the method proposed and the magneto-elasticmethod as well as the stress relief measurement detailed experimental study on the residual stress surrounding the coldexpanded tail bolt hole is performed. Relationship between the distribution of residual stress and cold expansion rateare established. The adaptability and limitation of theoretical predichon are also analyzed by comparing the theoreticaland experimental results.

A novel hole cold-expansion method and its effect on surface integrity of nickel-based superalloy

Preferred surface integrity around the hole wall is one of the key parameters to ensure the optimized performance of hole components for nickel-based superalloy.The novel hole cold expansion technique introduced in this work involves the laser texturing process(LTP)followed by the Hertz contact rotary expansion process(HCREP),where the cylindrical sleeve is the critical component connecting the abovementioned two processes.The purpose of LTP is to obtain the most optimized strengthened cylindrical sleeve surface,preparing for the following HCREP.Hereafter,the HCREP acts on the nickel-based hole components by the rotary extruding movements of the strengthened sleeve and conical mandrel tools.As compared to the as-received GH4169 material,the surface integrity characterization for the strengthened hole shows that a plastic deformation layer with finer grains,higher micro-hardness,deeper compressive residual stress(CRS)distribution and lower surface roughness is formed at the hole wall.In addition,transmission electron microscope(TEM)observations reveal the microstructure evolution mechanism in the strengthened hole.Grain refinement near the hole wall is regarded as the fundamental reason for improving the surface integrity,where the aggregated dislocations and recombined dislocation walls can be clearly observed.