The Establishment of Surface Roughness as Failure Criterion of Al–Li Alloy Stretch-Forming Process

Jing-Wen Feng,Li-Hua Zhan,Ying-Ge Yang

doi:10.3390/met6010013

Abstract

Taking Al–Li–S4–T8 Al–Li alloy as the study object, based on the stretching and deforming characteristics of sheet metals, this paper proposes a new approach of critical orange peel state characterizations on the basis of the precise measurement of stretch-forming surface roughness and establishes the critical criterion for the occurrence of orange peel surface defects in the stretch-forming process of Al–Li alloy sheet metals. Stretching experiments of different strain paths are conducted on the specimens with different notches so as to establish the Al–Li–S4–T8 Al–Li alloy, forming limit diagram and forming limit curve equation, with the surface roughness of characteristic critical orange peel structure as the stretch-forming failure criterion.

Highlights

Aircraft skin serves as the shape part of an aircraft and constructs the aerodynamic configuration of the aircraft, featuring big size and direct contact with air
In order to conduct synchronization tests on stress-strain and orange peel surface defect in the stretch-forming process of Al–Li alloy, a stretch-forming test and testing system are established to obtain the critical strain state of orange peel of the product, in which the optical deformation measurement instrument and the universal testing machine operate in collaboration, as shown in measurement instrument and the universal testing machine operate in collaboration, as shown in measurement instrument and the universal testing machine operate in collaboration, as shown in
Al–Li alloy metal morphology and true strain of the specimen at different speeds, when tiny orange peel phenomena sheet can be measured with the results shown in

Summary

Introduction

Aircraft skin serves as the shape part of an aircraft and constructs the aerodynamic configuration of the aircraft, featuring big size and direct contact with air. It requires an accurate shape, smooth streamline, and no surface defects, etc. Compared with other approaches to aircraft skin forming, the stretch-forming technology might cause surface defects such as orange peel. Orange peel affects the appearance of the aircraft skin, and damages its surface integrity. In the case of mirror skin, orange peel appears due to mirror skin’s internal structure and polished surface, seriously affecting its service life, which is usually the main reason for the scrapping of parts [8]

Methods

Results

Conclusion