| In engineering applications,engineering materials are subjected to compressive loads in most cases,except for a few cases where they are subjected to tensile loads,which indirectly causes tensile failure.However,in the study of tensile test methods,which may be not applicable to all hardness engineering materials because of the structural properties of the materials themselves.Therefore,it is meaningful to select engineering materials with different hardnesses for their tensile properties and reliability of test methods.Based on this,this thesis selects engineering materials of three different hardness grades,viz.mortar-granite,rigid polyurethane foam and silicone rubber foam.It mainly focuses on the following aspects.(1)Quasi-static tension of Mortar-Granite interface.The effect of positional relationship of aggregate between the top or bottom of mortar on the tensile properties of the interface was studied.The test results showed that the stress-strain curve of the specimens with aggregates on the top of mortar,which presented a significant linear growth relationship in the elastic deformation stage,and had a high Young’s modulus,tensile strength and obvious yielding phenomenon.(2)Dynamic direct tensile test of mortar-granite interface.It is found that the DIF value is increased with the increase of strain rate,and its rate sensitivity was also closely related to surface roughness of aggregates and aspect ratio of the specimens.That is,under the same loading pressure,the DIF value is decreased with the increase of surface roughness of the aggregate,so the average tensile strength of the ITZ is decreased with increasing roughness.In addition,the average tensile strength of mortar-granite ITZ had a significant downward trend with the increase of length-diameter ratio,and its decline will decrease with the increase of interface roughness of aggregates.(3)Study on dynamic split tests of mortar-granite interface.The effects of diameter,aspect ratio,roughness and strain rate on the tensile strength of ITZ were taken into account.It is found that the tensile strength of ITZ increases with the increase of surface roughness and diameter of the aggregates,and the significance is obvious.However,the aspect ratio and the loading pressure of the specimens had a certain influence on the interface strength,but it is not significant.(4)Study on dynamic direct tensile tests of rigid polyurethane foam.Studies had indicated that the yield behavior of the materials becomes more pronounced and the tensile strength increases significantly as the loading strain rate increasing,showing a certain rate sensitivity.Within the rod diameter range,for the same aspect ratio,the tensile strength of the rigid polyurethane foam gradually increases as the specimen size increases in fixed ratio increments.However,the fracture strain and strain rate of the specimens decreased with the growth of size.In addition,the average tensile strength reduced gradually with the increase of radial aspect ratio,and increased with the increase of axial aspect ratio.(5)Quasi-static and dynamic splitting tests of rigid polyurethane foam.Quasi-static and dynamic splitting tests of rigid polyurethane foams mainly consider the effect of strain rate and length-diameter ratio on their tensile properties and damage.The results showed that the tensile strength aggrandized with the increase of the strain rate in the quasi-static splitting test,and has a close relationship with the density that the greater the material density,the higher the tensile strength.The elastic modulus and yield strength of the materials also increased with the increase of the strain rate,while the tensile strength and elastic modulus decreased with the increase of the aspect ratio of the specimens.The DIF value increased significantly with the increase of the strain rate in dynamic splitting tests,which showed a non-linear increasing trend,and its tensile strength and elastic modulus decreased with the increase of the length-diameter ratio.(6)Quasi-static direct tensile tests of silicone rubber foam.The effect of temperature on tensile properties of silicone rubber foam was studied by means of fixture connection for specimens.The results showed that the tensile strength of SRF gradually decreased with the increase of temperature,while the tensile strength increased obviously after rewarming,and the Poisson’s ratio presented a trend of slow decline with the increase of loading time.The strain rate effect and size effect of SRF were studied by adhesive tension.It was found that the tensile strength of SRF increased with the growth of strain rate,but the elongation at break decreased with the increase of strain rate.Under the condition of constant strain rate loading,the tensile strength,strain and elastic modulus of SRF decreased with the increase of aspect ratio,and the elongation at break also decreased with the increase of aspect ratio. |
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