Investigation of prepreg bonded composite single lap joint

Adhesive bonded single lap joint has been used extensively in laminated composite structures. Using neat resin adhesives, however, the joint strength is comparatively low and the fabrication time is long. In order to increase the joint strength and reduce the fabrication time, two types of fiber pre-impregnated (prepreg) composites were used to bond composite single lap joints. Test specimens were prepared per ASTM D 3165-95 standard. Ninety days of accelerated conditioning using seawater and ultraviolet radiation were conducted to investigate the long-term performance of prepreg bonded single-lap joint in an offshore environment. The shear strength of various specimens was obtained using tension tests. Two types of neat resin bonded specimens were also used for comparisons. Finite element analysis was implemented to justify test results. Parameters affecting the load carrying capacity of prepreg bonded composite single lap joints were investigated based on finite element analysis results.     

Hygrothermal studies on syntactic foams and compressive strength determination

Syntactic foams are commonly used as core materials in composite sandwich structures for weight sensitive applications such as aircraft and spacecraft structures and boat hulls. Moisture absorption is highly undesirable in these applications. The present study evaluates the hygrothermal properties of two types of syntactic foams. Distribution of outer diameter of cenospheres (hollow particles) incorporated in both types of syntactic foams is the same but there is variation in the internal diameter causing difference in the density of syntactic foams. Epoxy resin is used as matrix material and the volume fractions of matrix and cenospheres are kept at 0.35 and 0.65 by volume, respectively. Moisture absorption experiments are conducted at two different temperatures, 25 and 70 °C and in deionized and salt waters. Non-destructive ultrasonic imaging technique is used to find the extent of moisture penetration and damage to the specimens. Syntactic foam samples are tested for compressive strength after moisture absorption and the results are compared with the compression test results of dry syntactic foam samples.     

A predictive model for ultrasonic attenuation coefficient in particulate composites

The increasing use of particulate composites in various weight sensitive applications such as aerospace and marine industries requires strict quality assurance methods. Non-destructive evaluation techniques such as ultrasound are currently used for characterization of these materials. Attenuation coefficient is one of the important parameters required for characterizing materials using ultrasound. Incorrect attenuation coefficient may lead to misdiagnosis of structures that could cause potential disaster. The present study focuses on developing a model for predicting the pulse-echo ultrasonic attenuation coefficient in particulate composites that takes into account the effect of particle size, porosity, and radius ratio. Attenuation loss from absorption, scattering, and resonance of glass particles is incorporated in the model. Interaction between the particles is neglected and the scattered energy is assumed to be entirely lost. Attenuation coefficient predicted from the model is compared with Yamakawa’s model and experiment.     

Effect of filler addition on the compressive and impact properties of glass fibre reinforced epoxy

Flyash is incorporated in glass fibre reinforced epoxies to study their response to the filler addition. Low cost of flyash can reduce the overall cost of the component. Only very low volume fractions of filler are investigated in the present study. To obtain further clarification of the observed phenomenon, another abundantly available low cost material, calcium carbonate is incorporated in one set of the specimens. Compressive strength of the material is found to decrease, whereas steep increase in impact strength is observed by introduction of very small quantity of fillers. Specimens containing calcium carbonate are tested for impact properties only. Effect of specimen aspect ratio on the compressive strength values is also studied by testing specimens of three different aspect ratios. Scanning electron microscopic observations are taken to develop a better understanding of the phenomena taking place in the material system at microscopic level.