The Research Of The Fatigue And Creep And The Dowel-type Connections Of Wood Plastic Composites

Wood-plastic Composite(WPC) offten has creep behavior under a load which is out of the elastic range, and are offten fastened firmly with bolts. Based on a large number of domestic and foreign documents concerning this subject, the fatigue and creep of WPC and dowel-type connections of three solid WPC across cross-sections were studied in the light of the engineering requirement. Some points have been drown out as follow:(1) The chapter 2 in this paper mainly used the Burger Model to analyse the creep behavior of the wood plastic composites. The results showed that Burger model fit accurately the creep curves of the material under different stress levels. Instantaneous elastic deformation and delayed elastic and viscous deformation increased with the increase of stress level. With the increase of stress level the stage of the instantaneous elastic deformation ends earlier and the WPC steps into the delayed elastic stage more quickly.Also,the stage of the delayed elastic stage ends earlier and the WPC steps into the viscous deformation stage more quickly with the further increase of stress level.(2)Sometimes fracture damage of wood plastic composites is due to the result of the action of fatigue and creep under dynamic load.This behavior of WPC under the mutual action of fatigue/creep was studied. Results showed that the curves of fatigue/creep had three stages at a 80% and a 60% breaking load, namely, the transient elastic deformation stage, the delayed elastic deformation stage and the accelerated fracture stage, the curves of fatigue/creep had foregoing two stages at a 40% breaking load. The delayed elastic deformation stage appears later,and bend deflection increases more quickly and breaking life decrease when the maximum load time is longer.(3)The chapter 5 used the EYM(European Yield Model) to simulate dowel-type connections in three solid WPC across cross-sections, and analyzed the breach character. Experimental research has shown that the EYM is sufficient to the design of WPC members with solid cross-sections. The load-displacement curve of the double shear connection in solid cross-sections have three stages, namely, the compactness stage, the critical cracking stage and the brittleness cracking stage. With the increase of distance from dowel to cross-section, the breaking load increases. At the same time with the increase of the bolt diameter, the breaking load also increases. With the increase of the distance from dowel to cross-section, the crack length increases. Synchronously with the increase of bolt diameter, the crack length also increases.