Design and Durable Failure Behavior of Bonding Joint for Polyethylene Wood Plastic Composites

Author:Zhou Dong Yan

Supervisor:zuo ming wei

Database:Doctor

Degree Year:2019

Download:38

Pages:136

Size:13862K

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As a new type of wood substitute material,polyethylene wood plastic composite(PE-WPCS)has the advantages of both wood and plastic,which made the development prospect broadly.In order to meet the application of wood-plastic composite materials and the demand of lightweight structure,bonding has become an important way of structural connection.In this paper,the single-lap adhesive joint of polyethylene wood-plastic composite is studied as the research object,through the research of different surface treatment methods,bonding technology,adhesive properties,bonding strength,stress distribution and bonding durability failure behavior,to design the single lap joint bonding Joint,and to realize the seamless connection of polyethylene wood plastic composite by using bonding technology and the rationality of joint design for bonding finally.The research of this paper can provide design ideas for the quick and effective connection of polyethylene wood plastic composite materials and the optimization design of adhesive joint.It has important theoretical value and practical significance for realizing the optimization design of bonding joint of polyethylene wood plastic composite material and expanding the application field of wood plastic composite materials.The polyethylene wood plastic composites are difficult to bond due to the polyethylene components with low surface energy and nonpolar within the composites.Reasonable surface treatment of polyethylene wood plastic composite is an important means to achieve adhesive bonding.The surface of polyethylene wood plastic composites was treated by a single jet plasma treatment,a combination of sanding followed by plasma discharge and a combination of sanding then coating with coupling agent,followed by plasma discharge respectively in the paper,and the test and analysis such as surface contact angle,surface free energy,surface morphology,Fourier infared spectrum(FTIR)analysis,XPS photoelectron spectroscopy analysis,combining with the test of bonding strength of adhesive joint and the analysis of joint damage type were also studied to discuss the effect of different surface treatment on the properties of polyethylene wood plastic composite,bonding mechanism and bonding durability of joint,and a relatively perfect surface treatment method for the bonding joint design of polyethylene wood plastic composite material was established.The results for test showed that the surface properties of polyethylene wood plastic composite changed greatly under the jet plasma surface treatment with single atmosphere and the combination of different surface treatment,and the surface wettability were improved,the polarity of materials surface increased,and a lot of polar groups such as-OH,C=O and-O-C=O were appeared on the surface of the materials.In addition,the chemical bond between the adhesive and the material surface was formed under the combination surface treatment of sanding then coating with coupling agent,followed by plasma discharge,which showed the synergistic effect of several surface treatments.After surface treatment,not only the adhesive strength of adhesive joint for the composite materials is greatly improved,but also the durability of adhesive joint is greatly enhanced.The surface treatment of the material is one of the important links in the joint design of polyethylene wood plastic composite.The durability of bonding joint can directly reflect the material properties and long-term use performance of bonding joint.After a combination of sanding followed by plasma discharge and a combination of sanding then coating with coupling agent,followed by plasma discharge,the surface properties and bonding properties of polyethylene wood plastic composite changed significantly under water environment of soaking and boiling for different periods of time.The results showed that the change of surface properties and bonding properties of polyethylene wood plastic composite by water molecules is the main reason for the decrease of bonding strength and the failure of bonding joints.The main reason of the failure of the bonding joint is the expansion of polyethylene wood plastic composite caused by water molecules and the internal stress within the joint material and the adhesive.The failure of the joint in natural environment is the result of the interaction of external complex environment.The stress distribution of bonding joint under stress state is also the key link in the design of bonding joint of polyethylene wood plastic composite materials.Based on the experimental results,the finite element model of single-lap adhesive joints and flat-lap adhesive joint of polyethylene wood plastic composite was established in this paper.The finite element numerical simulation of stress distribution of adhesive with different elastic modulus(epoxy resin,acrylic ester)and adhesive joint with different lap lengths was conducted by using ABAQUS finite element analysis software.The results showed that the lap zone end of polyethylene wood plastic composite bonding joint was the fracture failure point of adhesive joint.The stress distribution is closely related with the elastic modulus of the adhesives,and the change of geometric size for the lap zone length showed a less effect on the stress distribution,which provided a certain theoretical basis for the design of single lap bonding joint.There was a large stress concentration at the joint of lap area cover plate for the flat lap bonding joint,which can be used to judge that the parts are prone to fracture failure.This conclusion is consistent with the location of fracture failure of bonding joint in the test.The results of finite element simulation further showed that the elastic modulus and lap length of adhesive had little influence on the stress distribution of flat lap bonding joint,and the mechanical properties of flat lap bonding joint were closely related to the properties of polyethylene wood plastic composites.After the cooperative surface treatment,the interface bonding strength of the bonding joint for the polyethylene wood plastic composite material was higher than the cohesive strength of the composite materials.At this time,the fracture failure of the composite materials will occur in the bonding joint,which provided a certain guiding significance for the selection of the bonding material and the application of adhesive joint form in the design of bonding joint structure.