Experimental Investigation on Spall Fracture of 30CrMnSiNi2A Steel

Spall fracture is a damage that occurs in a body when two rarefaction waves interact and produce enough dynamic tension breakage,and then the spall zone is founded in the interior of the target.Behavior of materials in the spall phenomenon is strongly affected by the stress level,time of loading and so on.The spall properties of 30CrMnSiNi2A steel loaded by a gas gun were investigated using the planar impact experiment and the two-wave structural profiles of free surface velocities of specimens were recorded by velocity interferometer system for any reflector （VISAR） techniques.The Hugoniot elastic limit （HEL）,spall strength,spall thickness and strain rate were obtained in the plate impact experiments of 30CrMnSiNi2A steel specimens with different thickness.The result indicates that the values of HEL and spall strength increase with the increasing strain rate.The dynamic spall fracture and corresponding microscopic mechanism of 30CrMnSiNi2A at different strain rates were evaluated through the fracture analysis and fractography using a scanning electron microscope （SEM）.

Peeling behavior and spalling resistance of CFRP sheets bonded to bent concrete surfaces

In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer （CFRP） sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one curved specimens and seven plane specimens are studied in the paper, in which curved specimens with bonded CFRP sheets can simulate the concrete spalling in tunnel, culvert, arch bridge etc., whereas plane specimens with bonded CFRP sheets can simulate the concrete spalling in beam bridge, slab bridge and pedestrian bridge. Three kinds of curved specimens with different radii of curvature are chosen by referring to practical tunnel structures, and plane specimens are used for comparison with curved ones. A peeling load is applied on the FRP sheet by loading a circular steel tube placed into the central notch of beam to debond CFRP sheets from the bent concrete surface, meanwhile full-range load-deflection curves are recorded by a MTS 831.10 Elastomer Test System. Based on the experimental results, a theoretical analysis is also conducted for the specimens. Both theoretical and experimental results show that only two material parameters, the interfacial fracture energy of CFRP-concrete interface and the tensile stiffness of CFRP sheets, are needed for describing the interfacial spalling behavior. It is found that the radius of curvature has remarkable influence on peeling load-deflection curves. The test methods and test results given in the paper are helpful and available for reference to the designer of tunnel strengthening.

The mechanism of liquid dispersing from a cylinder driven by central dynamic shock loading

A systematic investigation on the mechanism of dynamic liquid dispersing process via theoretical and experimental approach is presented.The experiments include weak and strong constrained scenarios using the high-speed camera technique and the flash X-ray radiography technique.Based on dynamic analysis,one-dimensional characteristics analysis and some numerical simulations on the propagating processes of blast waves before the container shell rupturing,further and detailed analyses of the experimental results are presented.The effects of the liquid viscosity on the dynamic dispersing flow are also analyzed,and the spall fracture mechanism is explored.Thus,the dominating forces determining the dispersing liquid flow are revealed,that is,the stretching and shearing action due to the interaction of two reflecting rarefaction waves in opposite propagating directions.The influence of container shell strength on the dispersing liquid flow is also investigated,and the characters of cavitation layered in liquid before shell rupturing are uncovered.Results revealed that different shell material results in different cavitating layers.Then the different cavitating layers drive the different dynamic liquid dispersing process coming into being.The metastable liquid states caused by pressure drop and cavitation generation are discussed.

Cumulation of a spherically converging shock wave in metals and its dependence on elastic-plastic properties, phase transitions, spall and shear fractures

Consideration is given to results of experimental and theoretical investigations how alpha-epsilon phase transition in the unalloyed iron and the 30 KhGSA steel and its absence in the austenitic 12Kh18N10T stainless steel influence processes under explosive deformation of spheres made of these materials.Polymorphous transition is shown to significantly effect on:amount of explosion-products energy transferred to a sphere,evolution of the converging-wave structure and its parameters,profiles of stress wave and temperature T(R,t)for some Lagrangian particles along the sphere radius,character of energy cumulation under spherical convergence of waves.