This work emphasis on investigation of effect of hygrothermal aging conditions on the mechanical properties of nanoclay-glass fiber-epoxy composites. Composite laminates are prepared by "hand lay-up technique" with varied nanoclay and glass fiber weight percentage. Composites have undergone different hygrothermal conditions viz., cold and boiling soaking. Composite specimens are experimented for tensile and flexural strengths. The "design of experiment (DOE)" based on full factorial design (33=L27) is used to optimize the response variables. The design and analysis is done by using "MINITAB 16" software. Results revealed that, hygrothermal aging conditions (42.69% contribution to the tensile strength and 53.87% contribution to the flexural strength) have negative and maximum influence on the composites. Nanoclay (24.75 % of contribution to the tensile strength and 29.17% contribution to the flexural strength) and fiber weight parentage (30.23% contribution to the tensile strength and 16.25% contribution to the flexural strength) have positive influence on the composites.

AISI 4140 steel is one of the important category in the steels with wide range of applications including but not limited to automotive, general machinery, oil and gas industry. In the current study, an effort is made to understand the effects of heat treatment parameters, such as heat treatment temperature and holding time, on the mechanical properties of AISI 4140 steel, and to optimize these parameters to obtain the superior combination of mechanical properties. The three important heat treatments which are used in this study are annealing, normalizing and oil quenching. The heat treatment parameters such as temperature and time are varied at three different levels of 900, 925, and 950 °C, and 1, 1.5, and 2 h respectively. Using the full factorial method, total 9 experiments were carried out with all the possible combination of temperature and time as the variants. In each of the tests, hardness and impact energy values were evaluated using appropriate tests, while microstructural changes were analyzed through a scanning electron microscope (SEM). The results obtained through statistical analysis have shown that combination of 900 °C with 2 h for annealing, 919 °C with 2 h for normalizing and 944 °C with 1 h for oil quenching as the optimum combination of heat treatment parameters for superior combination of hardness and impact energy. Results showed that increasing temperature led to grain coarsening, reducing hardness but improving impact energy. Regression equations generated in this study which have R square value more than 90% may be used to predict the hardness and impact energy for any value of temperature and time which is within the range of values considered for this study.

The current work focuses on the natural aging phenomenon of a eutectoid steel powder-(0.8 wt.%) reinforced Al-Zn-Mg (Al 7075) alloy, which was subjected to a hybrid heat treatment. The hybrid treatment comprises the aging treatment of a matrix and the conventional treatment of a steel reinforcement in a single stretch on the stir cast composite. This material finds uses in space and transportation applications. The hybrid treatment consists of a conventional heat treatment cycle to obtain pearlite, bainite, and martensite phases in steel powder, followed by an age-hardening treatment for the Al 7075 matrix. This hybrid heat treatment resulted in improvements in the hardness and strength over the conventional aging treatment. The peak-aged hybrid specimens were subjected to natural aging in an open atmosphere for a continuous duration of 25 weeks to study the stability of the properties after peak aging. Tests of the mechanical properties such as the hardness and tensile strength along with microstructure analysis were carried out. During natural aging, the hardness of composites decreases irrespective of the quantity of the reinforcement in the composites and the type of reinforcement phase alteration during hybrid heat treatment. Also, the composites subjected to hybrid heat treatment show better resistance to natural aging compared to the conventionally aged samples. Within the group, the hybrid-treated martensite formed into a composite with 6 wt.% reinforcement showed only a 4% reduction in hardness during natural aging, which is an indication of a decent level of resistance to natural aging.