Study On The Creep Properties Of Wood Flour/High Density Polyethylene Composites Floor

Wood-plastic composites(WPC) is mainly used in the building field, such as satir treads、 railings、outdoor floor、building templates, et al. WPC is easy to present a creep phenomeon in using, especially when used outdoor, environmental factors may increase its deformation, leading brittle fracture suddenly, resulting in serious potential safety. This thesis focuses on the effects of cross-section shape, wood flour content, and loading on the creep properties of WPC. The geometric properties of the cross-section were calculated by AutoCAD software. RD-20electronic creep measuring machine was used to test24hours creep/24hours recovery of WPC floor. Using self-designed creep measuring device,1500h creep of WPC floor with different cross-section shape were tested. The creep behavior of WPC floor were simulated by the ten element model and the Findley power law model. The results showed:(1)The more wood flour content, the more greater the density of WPC was, the higher water absorption was. When wood flour content increased from50%to70%, flexural strength, elastic modulus increased by10%. and78%, respectively, but impact strength decreased by32%; storage modulus and complex viscosity of WPC significantly improved. When wood flour content increased from50%to70%, the creep strain decreased by56.8～59.2%. When wood flour content increased, the elastic deformation and the steady creep rate presented downward trend. After the creep and recovery, the difference of recovery rate of three kinds of WPC was small. The influence of temperature(except load) on creep behavior of WPC was the most significant, wood flour content took second place, relative humidity had little effect on the short term creep behavior.(2)The relation of section inertia of five kinds section shape of WPC floor was: rectangular hollow type>circular hollow type>solid type> circular open-end type>rectangular open-end type. The regular of section modulus in bending of different section shape agreed with the section inertia. The failure load of solid type floor was2.16～2.30times of rectangular open-end type floor, the failure load of circular open-end type floor was1.21～1.30times of rectangular open-end type floor. The difference in failure load of two kinds hollow type floor was small, a little less than that between solid type floor. The order of the elastic modulus of five kinds of WPC floor was:rectangular open-end type-circular open-end type> circular hollow type> rectangular hollow type>solid type.(3)Long-term and short-term creep tests showed that the creep resistance of floor of upper and lower structure approximate symmetrical was superior to the open-end type floor. The difference of creep deformation between two kinds hollow type floor was small, creep deformation of rectangular hollow type floor were a little less than circular hollow type floor, followed by solid type, creep deformation of rectangular open-end type floor was the largest. Under the same conditions, the steady creep rate of five kinds of WPC floor were consistent with their creep deformation law.24hours recovery tests showed that section shape had little effect on recovery rate. Wood flour content increased, creep deformation of WPC floor also decreased. The influence of load on creep behavior of WPC was the most significant. The fitting correlation coefficient of Burgers model was higher, but its fitting effect was poor at the decelerating creep stage. The ten element model and the Findley power law model fitted creep curves of WPC floor well in short term, correlation coefficient R2of fitting curves and experimental curves reached more than0.99. Comparison model prediction curves and test curves, it showed that neither ten element model nor the Findley power law model could predict long-term creep of WPC well.