h i g h l i g h t sLow-speed and high-speed direct tensile tests were performed on PVB material. Stress-strain curves were derived at strain rates from 0.008 s À1 to about 1360 s À1 . The strength was found to increase with strain rate; but PVB becomes less ductile. The testing results with available testing data were summarized and analyzed.
a b s t r a c tPolyvinyl Butyral (PVB) has been largely used as an interlayer material for laminated glass to mitigate the hazard from shattered glass fragments, due to its excellent ductility and adhesive property with glass pane. With increasing threats from terrorist bombing and debris impact, the application of PVB laminated safety glass has been extended from quasi-static loading to impact and blast loading regimes, which has led to the requirement for a better understanding of PVB material properties at high strain rates. In this study, the mechanical properties of PVB are investigated experimentally over a wide range of strain rates. Firstly, quasi-static tensile tests is performed using conventional hydraulic machine at strain rates of 0.008-0.317 s À1 . Then high-speed tensile test is carried out using a high-speed servo-hydraulic testing machine at strain rates from 8.7 s À1 to 1360 s À1 . It is found that under quasi-static tensile loading, PVB behaves as a hyperelastic material and material property is influenced by loading rate. Under dynamic loading the response of PVB is characterized by a time-dependent nonlinear elastic behavior. The ductility of PVB reduces as strain rate increases. The testing results are consistent with available testing data on PVB material at various strain rates. Analysis is made on the testing data to form strain-rate dependent stress-strain curves of PVB under tension.
Carbon fiber reinforced polymer (CFRP) has been extensively used to strengthen structures owing to its outstanding mechanical properties. With an increasing threat from terrorist bombing attacks and accidental explosions, the application of CFRP has been extended to mitigate the effect of blast loading on structures. A better understanding of the dynamic material properties of CFRP/epoxy laminates at high strain rates is therefore needed for more reliable analysis and design of CFRP strengthened structures under dynamic loadings. In this study, the unidirectional tensile properties of CFRP (SikaWrap®-230C) and epoxy resin (Sikadur®-330) laminates is investigated experimentally over a wide range of strain rates. Quasi-static and low-speed tensile tests are conducted at strain rates varying from 7x10-5 s-1 to 0.07s-1. Then, high-speed tensile tests are performed using a high-speed servo-hydraulic testing machine at strain rate from about 10s-1 to 240s-1. The testing results show that both the tensile strength and the stiffness of the CFRP/epoxy laminates are insensitive to loading speed when the strain rate is less than 50s-1. However, when strain rate is over 50s-1 , both the tensile strength and the coupon stiffness increase with the increase of strain rate. Highspeed camera images are used to assist inspecting the failure modes of CFRP/epoxy laminates. It is found that under high-strain rate tension CFRP/epoxy laminates fail differently from that at low-strain rate. The different failure mode is believed to contribute to the increment of laminate strength. The testing data are analyzed together with available testing results on CFRP/epoxy laminates at various strain rates. Empirical formulas of dynamic increase factor for CFRP material are derived for better prediction of material strength at various strain rates.
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