Failure and fracture micro-mechanisms in metal-composite single lap joints produced by welding-based joining techniques

Abstract

Welding-based joining technologies have been recently developed for metal-composite lightweight structures. In this work, the welding-based joining technology, friction spot joining, was selected to study the failure and fracture micro-mechanisms of an aluminum-composite single lap joint. Failure analysis suggested that the radial cracks nucleate at the periphery of the bonding area and propagate rapidly until failure of the so-called adhesion zone. Upon further loading the cracks propagate into the transition and plastically deformed zones leading to a reduction of the stiffness of the joint. The final stage of failure occurs rapidly in a catastrophic manner. The findings of the fractography using scanning electron microscopy demonstrated a mixed brittle-ductile fracture. Three zones were identified on the fracture surfaces: a smooth and featureless area known as the mirror zone demonstrating brittle fracture, a quasi-smooth area representing a mixture of ductile and brittle fractures and finally a zone with a highly rough surface implying ductile fracture of the composite part. Further, fiber pull-out and breakage were identified as additional fracture micro-mechanisms. All in all, metal-2 composite joints produced by welding-based techniques demonstrate a mixed brittleductile fracture.

Durability of Metal-Composite Friction Spot Joints under Environmental Conditions

“…Figure 11 shows the fracture surface of the four pre-treated joints after 28 days of accelerated aging. The dark aluminum hydroxide layer can be observed on the SB and CC pre-treated specimens even very close to the consolidated molten PPS (known as the Adhesion Zone (AZ) [4,52]), as indicated by the black arrows in the figure. However, in none of the joints could any indication of aluminum hydroxide formation inside the bonding area be detected.…”

“…However, in none of the joints could any indication of aluminum hydroxide formation inside the bonding area be detected. In FSpJ, strong micro-mechanical interlocking and/or adhesion forces between the aluminum and consolidated molten PPS significantly reduce the moisture diffusion into the Plastically Deformed Zone (PDZ) [4,52], the area inside the consolidated molten PPS. Therefore, the rate of the interface deterioration is reduced, as was observed from the residual strength of the joints, shown in Figure 7.…”

“…Figure 12a shows the fracture surface of the SB specimen on the aluminum side of the joint. The image illustrates the AZ with a very smooth surface at the top of the image followed by a Transition Zone (TZ) [4,52]. The TZ shows typical features, where PPS remains attached to the aluminum as individual islands [52].…”

Microstructure and mechanical properties of SiC-SiC joints joined by spark plasma sintering

“…Several studies on the use of SPS as a manufacturing technique for SiC materials have been published in the last decade [17][18][19][20][21][22]. In the field of materials joining, many studies have focused on metal-to-metal, ceramic-to-ceramic or ceramic-to-metal joints using conventional techniques [23][24][25][26][27][28].…”

Influence of Processing Parameters on Laser Direct Joining of CFRTP and Stainless Steel

“…As a result, the heat transferred to the surface of CFRTP is limited which cannot melt the PPS additive. Based on the former researches [35], the bonding e ect between the CFRTP and stainless steel is mainly in uenced by the bonding interface. Due to the great di erence between the stainless steel and CFRTP, there would be no atom or molecular binding.…”