Joining of aluminum and long fiber thermoplastic (LFT) composites.

摘要

Metal/polymer joints are used in variety of areas: aerospace, automotive, prosthetic devices, electronic packaging, etc. The present study involves a tailcone, which is currently made of aluminum and a new design will involve a joint between aluminum and long fiber thermoplastic (LFT) composite. The new tailcones were processed by insert molding, also called as extrusion-compression molding. Finite element (FE) models were used to obtain a temperature profile during cooling of tailcone from processing and to estimate thermal stresses generated. Experimental verification of the temperature profile was obtained by IR thermography. It was observed that the LFT part of the tailcone cooled faster than aluminum. During the cooling of the tailcone, the aluminum insert acted as a heat sink because of the large difference between the thermal conductivities of aluminum and the LFT composite. Thermal stresses computed were 2.5 MPa and 12 MPa in the case of beaded and threaded insert tailcones, respectively.;Static pullout tests were done to obtain an insight into the failure mechanisms of the joint between aluminum and LFT composite. Both the tailcone configurations, with beaded and threaded inserts, showed about the same average peak load, 96 kN. Radiographic and metallographic studies showed that the damage at the interface between aluminum and LFT composite occurred in the form of microcracks, followed by complete separation normal to the stress axis. The tailcones housed in projectiles were test fired and it was found that the HBTs disintegrated immediately after they came out of the barrel. A new design was proposed to overcome the drawbacks of the HBTs, called filled-back tailcone (FBT). Static pullout tests on FBTs showed no failure of the tailcones, which was in accord with the test firing where tailcone did not fail.;The study of aluminum/LFT composite interfaces was extended into the realm of laminated composites. Laminated composites were made in the form of alternate layers between LFT composite and metal (called as LMLs) such as aluminum by compression molding. Interlaminar shear strength of the laminates was determined by short beam three-point bend tests. It was found that the strength depends on the surface quality of the aluminum. ILSS in the case of mean roughness (Ra) 3.3 mum was 34.5 MPa, whereas 24 MPa in the case of mean roughness of 0.4 mum. Tensile test results showed that average Young's modulus and tensile strength of the laminate were 44.8 GPa and 244 MPa, respectively. Rule-of-mixtures predictions matched closely with the experimental results. Low velocity impact (LVI) tests showed that the specific perforation energy of the LMLs was significantly higher (7.1 J/kg m-2) than that of LFT composite (1.2 J/kg m-2). This new type of hybrid composite, LML, is quite promising for a variety of applications in automotive as well as aerospace industries.