Aircraft are exposed to significant temperature variations during flight. At high altitudes, they encounter extremely low temperatures, while some components experience elevated temperatures due to aerodynamic heating or the heat generated by engine operation. These conditions represent a major engineering challenge because the materials used in aircraft manufacturing must maintain their mechanical properties and ability to withstand loads despite continuous temperature changes. High temperatures affect the properties of many materials, potentially reducing their mechanical strength and hardness. They can also cause thermal expansion and dimensional changes, which may affect the accuracy of component assembly and the compatibility of connected parts. These effects are particularly important in engine components and parts located near heat sources. Special alloys, such as nickel-based superalloys, are used in these applications because of their ability to retain strength at elevated temperatures. Protective coatings and thermal barriers are also employed to reduce heat transfer and protect components from damage. In contrast, low temperatures can affect the behavior of certain metals by increasing their susceptibility to brittle fracture and reducing their ability to withstand impact, particularly when the material is unsuitable for cold environments. The external parts of aircraft, including wings and the fuselage, are exposed to severe thermal conditions during flight at high altitudes. Therefore, materials with suitable toughness and good resistance to fatigue and cracking must be selected. Aluminum alloys, titanium alloys, certain types of steel, and composite materials are important choices in aircraft manufacturing. The selection of each material depends on the function of the component and the operating conditions to which it is exposed. Another important aspect is thermal expansion and contraction. Materials expand when their temperature increases and contract when their temperature decreases. Repeated temperature changes can generate thermal stresses within components, particularly when different parts are made of materials with different coefficients of thermal expansion. Over time, these stresses may contribute to crack formation or weaken joints. For this reason, engineers consider the thermal properties of materials when designing aircraft structures and selecting appropriate joining and insulation methods. To ensure aircraft safety and reliability, materials used in aircraft manufacturing undergo rigorous testing. These tests include evaluating their resistance to heat and cold, measuring their mechanical properties under different operating conditions, and examining their ability to withstand repeated heating and cooling cycles. Computer simulation techniques and non-destructive testing also help predict potential problems and detect defects before they develop into serious failures. A thorough understanding of the effects of temperature on aircraft materials is essential for developing safer and more efficient aircraft capable of operating reliably under a wide range of environmental conditions. Assist. Lecturer Al-Buraq Haider Mohsen