A display and analysis system for hermetical flow field in water tunnel is developed based on the particle image velocimetry(PIV)technology.It consists of some subsystems,such as lamp-house,imaging,image processing and analyzing,control and particles putting.Taking the flow fields around a sphere and a cylinder model as an example under higher Renolds number 5.8×105 in water tunnel,we inquired into the application of the system to water tunnel experiment by cross correlation algorithm.The measure error is less than 2%.The test results show that the developed system can measure and display the flow field accurately in complex flow field without touching and disturbing.The research work indicates that PIV has lots of potential applications in the underwater flow field measurement.
The effect of strain rate on fracture behavior of poly(methyl methacrylate) was investigated.The uniaxial tensile rupture tests for the poly(methyl methacrylate) samples were carried out at different strain rates at ambient temperature.It is found that the elastic modulus of the material increases with increasing strain rate,while the elongation is reversal with strain rate.Simultaneously,there exists a critical strain rate within which the stress-strain curves overlap one another,and beyond which the curves depart from each other.The amount of energy added to the system due to work done by the imposed load was calculated,and the strain energy stored in the material at each strain rate was calculated by the current stress integral with respect to strain.The complementary strain energy,which is the difference between the work and the strain energy,was obtained and was considered to supply the surface energy to create a new crack surface in the polymeric material.It is found that the work done by the imposed load,which is needed for the fracture of poly(methyl methacrylate) sample,decreases with increasing strain rate,and the strain energy decreases with strain rate as well,which demonstrates that the polymeric material at high strain rate is easier to fracture than that at low strain rate.As the strain rate increases,the fracture mode changes from ductile,semi-ductile to brittle mode.The complementary strain energy almost sustains a constant at any strain rate.The density of surface energy,which characterizes the energy per unit area needed for creating crack surface,is a strain rate-independent material constant.
