Abstract
Retrofitting steel plates with shape memory alloy fiber-reinforced polymer(SMA/FRP)patch has become an attractive research direction,which may create reliable retrofitting of existing structures.
The considerations of the most important experimental rest results were obtained from the experimental studies,so the synthesis of research results is divided into the following macro-themes,such as the bond between SMA(wires)and FRP,recovery stress of SMA,influence of materials and surface treatment,and the fatigue life of SMA/FRP/steel plate composite.
SMA/FRP composite has shown its superiority in strengthening cracked components.All of these tests were under pull-out tests,and these patches related to bonding single,three,ten and a sandwich of SMA wires embedded FRP patches[1-3].To strengthen or retrofit any steel plates,it is very important to understand the common failure modes because debonding was considered to be a major failure mode in SMA/FRP patches,and to improve fatigue life.
The FRP composite patches can bond with cracked metal structures to decrease the stress range near the crack tip and increase the fatigue life.It was proposed to use SMA material to achieve this prestressing effect embedded FRP patch by using the electric current,heating source and water heating.Subsequently,a novel strengthening technique was proposed by El-tahan M et al.[1]using SMA/FRP composites as partially activating prestress by SMA wires which obtained the maximum stress.To make nice performance active hybrid SMA/FRP composites,it is very essential to study the ef fect of SMA prestress to apply these patches to steel elements.
Properties of materials are very important for the improvement of bond properties.Among the composites has FRP,SMA,epoxy adhesive and steel plate.Also,the reinforcing effect of FRP with different elastic modulus provided dif ferent results of fatigue life studied by many authors.According to previous researches,the fatigue life was the same when the tensile stiffness of FRP was identical[4],however,the higher elastic modulus,the higher fatigue life.Moreover,the number of the SMA wires provided the improvement of fatigue life.A lot of SMA wires can increase the fatigue life ratio that experiments were done with the quantity of SMA wires proposed[3,5].Then,the surface treatment used for bond of composites with steel plate that had been conducted by many researchers.On the other,the effect of surface treatment of steel plate through means of grit blasting,needle gun,wire brushing,and rotary wheel,and from the results the advantageous effect on the fatigue life shown.
In general,SMA/FRP patch-steel reinforcement methods include bond the patch to the steel surface with structural epoxy adhesives.Then,there are several failure modes of SMA/FRP patches which was bonded with steel plates under tension fatigue load.Among of these failure modes,the new findings were SMA and adhesive interface debonding,and SMA pull-out[3,5],as shown in Figure 1.Additionally,epoxy adhesives are a very important connection between steel plate and SMA/FRP patch to grow fatigue life.The study conducted by Li et al.[6]used different adhesives with FRP to investigate the central inclined cracked steel plates that applied a prestressed and non-prestressed system as well as El-tahan M et al.[2]compared both adhesives which were tested to evaluate mechanical properties.The results demonstrated that they powerfully contributed to the failure modes that were the main factor of fatigue performance for applications in any structures.Therefore,epoxy adhesive bonded steel plates to SMA/FRP patch which provided structural strengthening,and analyzed failure modes were essential to improve the cycles of fatigue life in this composite.
Figure 1 Failure modes of SMA/FRP patch repaired specimens
Finite element method(FEM)was utilized in this study.Moreover,many researchers have studied the fatigue life of all steel plates bonded with SMA/FRP patches analyzed by ABAQUS predicted and tested[3,4,7].The finite element results showed that the SMA/FRP patch had good agreement observed between the predicted and the experimental test which had the longest fatigue life performance.Therefore,all these findings are summarized in Figure 2 and Table 1.
Figure 2 The fatigue life of steel plates
Table 1 Finite element methods
Furthermore,SMA/FRP/steel composite materials need the following contents to study including stress transfer regularity of SMA/FRP composite with steel members after activation,and crack initiation direction and crack propagation law of steel members withⅠ/Ⅱcracks strengthened by SMA/FRP composite under axial tension fatigue load.All of the central point focus on future work.
Based on the review demonstrated shows the SMA/FRP patch can be effectively utilized as a retrofit system.The summaries of SMA/FRP/steel plate composite are followed by experimental test results,numerical methods and future research directions depending on the state-of-the-art.