Three‐point flexural fatigue behaviour and mode I interlaminar fracture toughness of the carbon fibre reinforced polymer composites (CFRPCs) modified by the addition of graphene nanoplatelet (GnP) were investigated. CFRPCs without any addition of nanoparticles were also tested as control samples. Fatigue life was characterized by the two parameter Weibull distribution function and predicted using the combined Weibull and Sigmoidal model. It was found that incorporation of very small amount (0.1%) of GnP in the epoxy polymer matrix improved mean and predicted fatigue life up to 155% and 190% (0.5 failure probability), respectively. The critical mode I interlaminar fracture toughness of the GnP reinforced composites was found up to 40% higher than the control samples. The improvement achieved by incorporating GnP is discussed in terms of crack deflection mechanism by nanoparticles and scanning electron micrograph images of the fracture specimens that revealed strong interfacial bonding in the nanoreinforced specimens.

Fiber reinforced polymer composite (FRPC) materials are superior to other conventional materials because of their high strength to weight ratio, corrosion resistance, and moisture resistance. FRPC materials are preferred in many high-end applications such as marine, automobile, aerospace, and advanced sporting goods. The aim of this study was to investigate the in-plane quasi-static compressive and durability studies of nanophased FRPC materials. Composite samples were fabricated using unmodified epoxy and epoxy modified with montmorillonite nanoclay (MMT), graphene nanoplatelets (GNP), and a combination of the two as a binary reinforcement with carbon fibers. Quasi-static compression tests were conducted for mechanical property evaluation. Seawater conditioning was performed for a six-month period both at room and arctic cold temperatures. The results indicated that addition of GNP and MMT improved the compressive properties of carbon/epoxy composites compared to unmodified carbon samples. Specific compressive strength and modulus of GNP infused samples improved by 30 and 41% respectively; the samples showed a relatively higher strain to failure than the unmodified samples. Specific compressive strength and modulus increased by 32 and 47%, respectively, for carbon/epoxy samples with MMT reinforcement. Performance of hybrid carbon/ glass/epoxy composites was lower compared to other FRPC materials considered in the study. The mode of failure of fractured samples investigated using scanning electron microscopy (SEM) showed a rough morphology after incorporation of nanoparticles into the polymer matrix. This is indicative of enhanced interfacial bonding between carbon/epoxy and the nanoparticles.

3-point flexural fatigue and Mode I interlaminar fracture tests were done to study the fatigue life and fracture toughness of nanoclay added carbon fiber epoxy composites. Fatigue life data was analyzed using Weibull distribution function, validated with Kolmogorov-Smirnov goodness-of-fit, and predicted by combined Weibull and Sigmoidal models, respectively. The nanophased samples showed more than 300% improvement in mean and predicted fatigue life. At 0.7 stress level, the nanophased samples passed the ‘run-out’ fatigue criteria (106 cycles), whereas, the neat samples failed much earlier. The interlaminar fracture toughness of nanophased samples was also enhanced significantly by 71% over neat samples. Optical and scanning electron microscopic images of the nanophased fractured samples revealed certain features that improved the respective fatigue and fracture properties of the composites.

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This is an Accepted Manuscript for the Microscopy and Microanalysis 2020 Proceedings. This version may be subject to change during the production process.

Electronic packages are frequently exposed to thermal cycling during their service life between low to high temperature extreme. Similar phenomena can be observed in solder joints during the characterization of thermal-mechanical fatigue behavior. This variation in temperature causes the evolution of mechanical and microstructural behavior of solder joints. Also, dwelling at high temperature extreme causes the mechanical properties reduction of solder joints due to thermal aging phenomena which eventually leads to the change in microstructure. In literature, the effect of thermal aging on the mechanical behavior evolution has been reported by several research groups, but the evolution of mechanical and microstructural properties under different thermal cycling exposure is limited. In our prior study, reduction of mechanical properties of SAC305 lead-free solder material under different thermal cycling exposures have been reported for up to 5 days of thermal cycling. It was found that thermal cycling with long ramp period and dwell time has severe effect on mechanical properties reduction. In our present study, previous study has been extended up to 100 days along with the mechanical behavior evolution of solder joints under stress free condition at different thermal cyclic loading. Particularly, the evolutions of mechanical behavior in both bulk SAC305 miniature solder bar samples and small SAC305 solder balls under stress free condition have been investigated for several thermal cycling profiles, and then the results were compared. Reflow solidification technique with a controlled temperature profile has been used to prepare bulk solder specimens for uniaxial tensile testing. Optical microscopy has been used to figure out the single grain BGA solder balls after grounding and polishing to avoid grain orientation effect during nanoindentation technique. Then, both bulk solder bars and solder balls were thermally cycled between −40 C to +125 °C under a stress-free condition (no load) in a thermal chamber. Several thermal loading were adopted such as (1) 150 minutes cycles with 45 minutes ramps and 30 minutes dwells, (2) air-to-air thermal shock exposures with 30 minutes dwells and near instantaneous ramps, (3) 90 minute cycles with 45 minutes ramps and 0 minutes dwells (thermal ramp only), and (4) Isothermal aging at high temperature extreme (no cycle). After each thermal cycling exposure, mechanical properties evolution of both solder bars and solder balls were recorded in terms of effective elastic modulus (E), hardness (H), yield strength (YS), and ultimate tensile strength (UTS). For the BGA solder balls, the evolution of mechanical properties was measured using nanoindentation. Moreover, mechanical properties evolution of both specimens was compared in terms of normalized properties with respect to elapsed time under different thermal cycling exposures. Finally, the microstructural evolution of bulk solder bars was observed under slow thermal cycling exposures with elapsed time.

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