Analysis Of Thermal And Mechanical Properties Of Fiber Reinforced Polymer Composites With Fiber Waviness

Fiber reinforced polymer?FRP?composites are prone to fiber wrinkle defects during the manufacturing process.Fiber wrinkles can weaken the mechanical properties of composite laminates,especially on compressive strength.Therefore,it is necessary to study the failure behavior of FRP composite with fiber waviness under compressive loading.In this paper,theoretical analysis and numerical simulation are conducted to investigate the mechanical properties of composite laminates with fiber-wrinkles.A progressive damage analysis is proposed for the laminates to obtain the relationship between the residual compressive strength and the wrinkle parameters.The contents and conclusions of this paper are as follows:?1?Firstly,based on three-dimensional heat transfer theory,numerical simulation of transient thermal conduction of resin laminates caused by fiber wrinkles was performed.The effect of geometric parameters of the resin accumulation zone on the change of the thermal resistance in the laminates and the thermal contrast on the surface of the laminates were analyzed.The feasibility of Infrared thermography on damage detection for laminates with resin accumulation was verified by experimental study.It is found that the change of the thermal resistance increases linearly with the area ratio of the resin accumulation zone to the cross section of the laminate.When the area ratio is 0.278%,the peak value of thermal contrast can reach 46 m K.?2?The theoretical analysis of the equivalent elastic constants of laminates with uniform fiber waviness,graded fiber waviness and local waviness are carried out.The progressive damage was simulated for laminates with uniform waviness and graded waviness under axial compression.The results show that among all the equivalent elastic coefficients,E_x and G_xz are most sensitive to the dimensionless parameter A/L.For the case of uniform waviness,four damage modes all occur on both sides of the peaks and troughs of the waviness,in which delamination and the matrix-fiber shear damage occur at the first time.The compressive strength of laminates decreases nonlinearly with the increasing of A/L.When A/L=0.2,the compressive strength reduces to 11%of the unfolded compressive strength.For the case of the graded waviness,matrix-fiber shear damage and delamination damage both occur in the maximum misalignment angle,while the fiber fracture occur in the surrounding zone of the peak and the maximum misalignment angle.?3?The progressive damage of fiber-wrinkled laminates with single and two resin rich zones under axial compression were simulated.The results show that the maximum normal stress occurs mainly at the top and bottom of the resin accumulating zone?i.e.the crests and troughs of the fold wave?,while the maximum shear stress occurs at the maximum misalignment angle.For the case of a single resin accumulation zone,the fiber fracture occurred mainly at the top and bottom of the resin accumulation zone,while the delamination damage occurs at the maximum misalignment angle.The compressive strength decreased nonlinearly with the increase of the height of the resin accumulation zone.When the height is about 27.8%of the plate thickness,the compressive strength reduces to 77.5%of the strength of the laminates without defects.The kinked bands form at the junction zone of the two resin rich regions,with severe fiber fracture and delamination damage.Fiber breakage occurs at the top or bottom of the two resin rich zone closest to the edge of the laminate.