Experimental Study On The Influence Of Damp Heat Aging On The Dynamic And Static Mechanical Properties Of PVC Foam

With the increasing demand for light-weight ship manufacture and marine equipment,composites have become more widely used in these areas.PVC closed cell foams are widely used with composite sandwich structures as core materials due to their superior properties.Foam sandwich structures for shipboard and marine engineering inevitably face the impacts of dynamic loading and wet thermal aging effects in their service environments,and it is particularly important to study their mechanical response under dynamic loading and wet thermal aging effects on foam performance.Therefore,in this paper,the research was conducted on the dynamic and static mechanical properties of PVC foams after treatment with different hygrothermal aging conditions,aiming to explore the effect of hygrothermal aging on the mechanical properties of foams and provide a reference for the design and material selection of the composite sandwich structure.The specific research contents are as follows:1.The wet heat aging experimental temperature which can reflect the actual working condition was set according to the application environment of PVC foams in the field of ships and marine equipment,a freshwater wet heat aging control group was set to contrast the effect of different wet heat raging waters on the mechanical properties of foams,and a 75°C high-temperature aging temperature was set to accelerate the aging process.2.Early water uptake behavior of foams during wet heat aging experiments was observed,combined with Fick’s law,to obtain the diffusion coefficient of water inside foams at different aging temperatures and water environments,to analyze the effect of different aging conditions on the water uptake properties of foams,and to obtain the mechanism of water uptake of foams under wet heat aging conditions.3.Static mechanical properties studies were carried out on compressive specimens aged wet and hot for 270 days as well as on tensile,three-point bending specimens aged wet and hot for a short period of 1-4 weeks.The effects of different moisture and heat aging treatments on the static mechanical properties of foams were analyzed.Found that wet heat aging had little effect on the static compressive properties of foams,because the post curing and consolidation stresses caused by short-term wet heat aging treatment both released tensile mechanical properties,and the foam bending properties decreased due to wet heat aging effects.4.Impact compression experiments were performed on three kinds of dense foams treated with 270 days of long-term wet and heat aging using a lengthened Split Hopkinson Press Bar(SHPB)apparatus.Dynamic mechanical properties of the foams before and after wet heat aging were obtained,and PVC foams were found to be strain rate sensitive,and the effects of foam density,wet heat aging environment on the strain rate sensitivity and dynamic mechanical properties of the foams were analyzed.5.The microstructure,thermal stability,and chemical structure of the foams before and after wet thermal aging were analyzed by scanning electron microscopy(SEM),differential scanning calorimetry(DSC),and Fourier infrared spectroscopy(FTIR).It was found that post solidification and degradation phenomena occurred during the wet heat aging of foams,and the high temperature and seawater aging environment contributed significantly to post solidification as well as degradation of foams.