RESPONSE OF A COMPOSITE CRUCIFORM SPECIMEN UNDER BI-DIRECTIONAL LOADING

Som R. Soni, Charles Cross, Gary Terborg

ABSTRACT

Integrated High Performance Turbine Engine Technology program (IHPTET) and Versatile, Affordable, Advanced Turbine Engines (VAATE) goals are very challenging and cannot be met without the innovative use of fiber reinforced composites. Because of unique light weight and high strength thermomechanical properties of composites, their use is increasing in different engine component applications. The challenge lies in the proper selection of the material, fiber and material constituents/ ratio, loading direction and environmental protection mechanisms. There are numerous materials available in market with different characteristics. Some of them are better characterized than others. We have selected Glass/VCAP-75, Glass/AMB-21, AS4/3501, A193-P/3502, IM7/5250 and NCT-350-TR50 composites for this investigation. The main reason of selecting these materials is to leverage the materials from different past and current projects.

Glass/VCAP-75 and Glass/AMB-21 woven fabric, polymer matrix composites (PMCs), are potential high temperature materials being considered for aircraft engine duct applications. Both of these material systems have been subjected to a considerable amount of mechanical testing, including bi-directional combined tension and bending as well as bi-directional in plane loading. For both material systems, the 12-ply laminate orientation is (0/45)3S. A number of effective material properties including compressive, tensile and shear moduli of these materials have been measured by researchers at AdTech [1]. These properties are utilized for predicting the response of cruciform laminate [4].

AS4/3501, A193-P/3502, IM7/5250 and NCT-350-TR50 composites are widely characterized material systems and have found place in airframe, aircraft engine, rocket systems, and satellite applications. Most of the experimental work done has been under unidirectional loading conditions. Very little work is done under multidirectional loading.

This paper deals with the stress and strength analysis of cruciform specimen shown in Figures 1 and 2. Both analytical and experimental studies are conducted. A general purpose FEA software (SDRC I-DEAS) is used to develop a finite element model to conduct the stress analysis of a composite specimen under bi-directional loading conditions. The loading is in the x and y directions of the specimen. At the intersection of the cruciform legs, two types of curvatures are considered to create different stress concentrations. One increases the stress concentration while the second decreases the stress concentration at the intersection. The representative case finite element results for maximum stress components for both kinds of specimens are given in bar chart form [4]. These results give an indication of the possible in-plane mode and location of failure. The experimental results are compared with the FEA predictions. Failure loads for specific loading is calculated by using the computer code [2] called, “Automated System for Composite Analysis”, (ASCA). The newly developed unique multi-axial testing system in the Turbine Engine Fatigue Facility of the Propulsion Laboratory, Air Force Research Laboratory (AFRL/PRTC) at Wright Patterson Air Force Base is used. A comparison between experimental and predicted results has been done. To clarify the difference between the predicted and observed load values, further investigation in determining the interlaminar stresses is carried out. The interlaminar stress components along the width of the cruciform arms are given in this paper. Also the relevant work to be done in the future is also given.