Effect of Thickness and Lay-up Sequence on Spring-in for L-shaped CFRP Beam

Abstract

The use of composite material is increasing now a days, especially in space applications, aeronautical industries and sports equipment because of their high strength to weight ratio. This study focuses on manufacturing of Carbon Fiber Reinforced Plastic (CFRP) L-shaped part. While making CFRP parts with oven curing process dimensional control is difficult because of residual stress induced in parts and distorts the part when part is removed from mold. This deformations are known as spring-in in angled parts and warpage in flat parts. There are several parameters like part thickness, lay-up sequence of laminate, applied pressure, curing cycle, tool material, surface roughness of tool, etc. affecting spring-in and warpage. In this dissertation, how thickness and lay-up sequence affects spring-in of L-shaped beam of CFRP is discussed. The design of experiment has been carried out and results are compared and analyzed using Minitab 17. The experiments have been performed for 4 and 8 layers of Hin-preg with different lay-up sequences. The aluminum is used as tool (mold) material to get more spring-in because of higher difference of coefficient of thermal expansion (CTE) between tool and part materials. The final L-shape parts have been prepared using oven heating curing process. Spring-in is measured using profile projector and Mitutoyo universal bevel protector. The thickness for laminate is measured using digital micrometer. The optimum value for thickness and lay-up sequence for minimization of spring-in has been determined. The experimental results shows that as thickness of part increases spring-in decreases whereas symmetric and balanced lay-up sequence used, spring-in decreases compared to unsymmetrical lay-up sequence.