ABSTRACT

Polymer composites are known for many attractive properties but their impact-induced resistance is poor. Impact of a foreign body affects the strength of composites considerably. Compression After Impact (CAI) properties becomes a critical parameter in design of structures especially in the aerospace applications. Thus one needs to perform impact tests on the polymer composite panels under controlled conditions and then determine compressive strength.

An air gun test setup is used to perform the impact tests under controlled conditions. An aluminum striker is used to impact the FRP panels. The velocity of the striker bar is measured with the help of a laser beam intersecting the striker bar and recording the pulse on a digital oscilloscope. The velocity of the striker bar is controlled to have desired impact energy. 

Two types of specimens are used to determine the compressive strength after impact, (i) glassfiber angleply laminate (GAL) and (ii) glassfiber fabric laminate (GFL). After conducting experiments it is seen that the compressive strength of GAL specimens after impact is 15.7 MPa and that of the GFL specimen is 58.5 MPa. In comparison to GAL, the GFL specimens are thus found to possess considerably higher compressive strength after impact.
T-Joints are extensively used to make large FRP structures as one piece especially in aerospace industries. Impact of a foreign body affects the strength of T-Pull specimen considerably. A test facility to determine the tensile strength of T-Pull specimens after it is impacted by a striker bar is designed, fabricated and made functional. One test was performed on an unimpacted T-Pull specimen, supplied by NAL Bangalore  to establish that the setup works well.

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