Development and testing of an intelligent hybrid polymeric composite beam embedded with Ni-Ti shape memory alloy with crack growth retarding ability

摘要

Hybrid Polymeric Composites (HPC) structural materials pose a challenge of developing microcracks and delaminations under impact and dynamic loads. This paper presents the development and testing of an Intelligent Hybrid Polymeric Composite (IHPC) beam embedded with Ni-Ti Shape Memory Alloy (SMA) with crack growth retarding ability. Upon heating to austenite finish temperature (Af), Ni-Ti SMA wire contracts as a result of detwinned martensite-austenite phase transformation. The contraction of the SMA was utilized to stiffen and retard crack growth in the IHPC beam, hence resulting to an increase of mode I fracture stress intensity factor (KIC). The SMA wire specimens were aged at 250°C, then prestrained at 3% in order to stabilize austenite start (As) and austenite finish (Af)transformation temperatures. The values of Asand Affor Ni-Ti SMA were determined. The IHPC and Polymeric Virgin (PV) notched beams were fabricated from epoxy resin. A four point bending test was performed on the beams to determine the effect of actuated Ni-Ti SMA on mode I fracture stress intensity factor KIC. The test was done at two temperatures, at T1 (below As) and at T2 (Af). Results showed that actuation of the Ni-Ti SMA increased the value of KICfor IHPC beams at T2 by 189% over the value of KICfor PV beams at T1. Actuation of the Ni-Ti SMA increased the value of KICfor IHPC beams at T2 by 41% over the value of KICfor IHPC beams at T1. Results showed that at T1 the loaded PV and IHPC beams fractured with unsteady crack propagation, while at T2 the loaded IHPC beams fractured with steady crack propagation. An increased value of KICand steady crack propagation at T2 indicated that the SMA improved the crack retarding ability of the HPC beam.