An investigation on the bearing test procedure for fibre-reinforced aluminium laminates

Excellent fatigue, static strength and damage tolerance characteristics together with low density make fibre-reinforced aluminium laminates a prime candidate sheet material for application in fatigue- and fracture-critical aircraft structures. Their use requires that mechanical property design allowables be established for incorporation in design handbooks (e.g. MIL-HDBK-5). An experimental programme based on statistical design was conducted to establish a meaningful test procedure for determination of fibre-metal laminate bearing strength design allowables. The test procedures investigated are the pin-type bearing test method (ASTM E-238) and the bolt-type bearing test method, a modified method based on the procedure for bearing strength determinations in plastics (ASTM D-953). Results are presented from an experimental programme which measured the bearing strengths of two grades of S-2 glass-based and one grade of aramid-based aluminium laminates. The influences of lateral constraint and ply orientation on bearing strength and failure mode are shown. The bolt-type bearing test method, which combines the attributes of the two aforementioned methods, is recommended. The study also showed that the bearing properties for edge distance ratio e/D = 2 can be predicted by correlation with the aluminium volume fraction in fibre-reinforced aluminium laminates. In addition, diagrams of joint structural efficiency, shown to be comparable to those of aluminium alloy sheets, have been established.