Date of Award

4-10-2024

Document Type

Thesis

School

School of Mechanical Engineering

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

Dr.V.M.Sreehari

Keywords

FGM, Buckling, Vibration, Thermal Environment, Spark Plasma Sintering

Abstract

Most aerospace applications involve structural components with a high stiffness-toweight ratio and excellent resistance to high temperatures. Buckling, vibration as well as other forms of instability are the consequences of a non uniform stress field caused by non uniform, localized edge loadings and the presence of discontinuities. In order to improve structural properties and increase load bearing capacity, designers concentrate on structural integrity, especially in high-temperature applications. The adaptability and customizable nature of functionally graded material (FGM) make it valuable in addressing these challenges.

Metal-ceramic FGM is an advanced composite material that integrates the distinctive qualities of metal and ceramic in a single volume and has mechanical properties that vary continuously and smoothly in spatial coordinates from one location to another. FGM technologies are still being researched and developed, which is expanding their potential and uses in the development of aerospace systems and technology. This work attempts to numerically evaluate the buckling and vibration characteristics stiffened and unstiffened FGM plates/shells with cutout under various mechanical and thermal load.

The buckling and vibration characteristics of both FGM plate and FGM shell are deteriorated by the influence of cutout and three stiffener patterns are introduced to enhance the characteristics. The ring stiffener provides good buckling characteristics and a maximum of 42% increase for the SSSS-edged FGM plate with k = 1, a/h = 10, and a cutout ratio of 0.5 when exposed to uniaxial UVL inplane compressive loads. Even though the straight stiffener exhibits good vibration characteristics than other stiffener patterns, the natural frequency is reduced by all stiffener patterns.

Additionally, the buckling load parameter, natural frequency parameter and critical buckling temperature decrease with an increase in temperature irrespective of the stiffener patterns and quantified the same. The effect of the uniform thermal environment and linear temperature rise from metal-rich to ceramic-rich regions on critical buckling temperature and free vibration characteristics of re-entry vehicle nose structures made of various FGM have also been examined. Finally, microstructural evaluation and various mechanical tests have been conducted on FGM plate fabricated using spark plasma sintering.

The SiC matrix grows progressively from the Al-rich layer to the SiC-rich layer, as demonstrated by the SEM investigation. No obvious gaps or delamination at the interface between any two layers are observed. The ultimate stresses for the tensile and compression tests are 139 MPa and 242 MPa, respectively. The natural frequencies were also determined experimentally as 820.3 Hz for first mode and 3203.1 Hz for second mode. The SiC-rich layer and the Al-rich layer had average hardness values of 122.42 and 58.81 HV, respectively. Thus, the current research contributes to detailed insight on the metal-ceramic FGM structures which help the designers in aerospace domain.

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