Question

1. How do the properties of the alloys exhibiting excellent casting behavior compare to the properties of the alloys exhibiting excellent metal cold forming?

2. about the trade off one makes using an alloy designed for casting versus and alloy designed for strain hardening?

3. what are the benefits of using composites versus aluminum alloys for commercial aerospace applications. Also, over what time frame do you expect the benefits to balance the cost?

Answer 1

1 answer. 2.answer.
Design Influence The metalcasting process offers freedom of geometry allowing sting design to play a key role in mechanical performance. Sections of a cast part subject to higher stress can be enhanced while low-stress regions can be reduced. This flexibility can help cast a part with optimum performance and reduced weight, both of which minimize cost. It is feasible to cast any geometry, but this may increase cost. When in the preliminary design stages, it can be advantageous to work with a metalcasting facility. Metalcasters have the technical expertise to assist with the casting design and material selection To develop a good casting, first reduce the number of isolated heavy sections because junctions within a casting should be designed not to add mass. When working with metalcasters, datum points should be stated, and machine stock should be added to required locations. Section thickness in a casting should be changed through smooth, easy transitions, which can be achieved by adding taper and large radi. Draft should be added to the design dimensions, but metal thickness must be maintained. The amount of draft recommended under normal conditions is 1.5 degrees. Further, reducing undercuts and internal geometry help minimize cost. The metalcasting facility and customer also should agree upon tolerances because specifying as-cast tolerances is important in minimizing cost.

Material Influence When selecting a steel, it is important first to know the required properties. The chemical composition and microstructure of a steel casting determine its mechanical properties. Heat treatment can change microstructure and provide a wide range of mechanical properties. A steel with high hardenability will have more uniform hardness in thicker sections than a steel with low hardenability. In general, adding alloying elements improves some properties but increases cost and may reduce other properties. However, most elements will increase the hardenability of steel Carbon should be kept as low as possible to maximize weldability. Minimizing alloying elements to safely meet the performance requirements of the item will reduce cost. Here, metalcasting firms can provide assistance with material selection to ensure that the appropriate properties are purchased Performance Condition:s Design requirements are typically determined in terms of strength or maximum stress. The design is commonly constrained by modulus, fatigue, toughness or ductility Increasing the strength of steel normally reduces the ductility, toughness and weldability. Therefore, it often is more desirable in steel casting design to use a low-strength grade and increase the section size or modify the shape. The design freedom makes castings an attractive way to obtain the best material performance as well as the needed component stiffness and strength. When designing a part, it is important to understand the limits of the design so the proper material selection can be made. Stress, strain, fatigue, impact, wear, creep and corrosion all are common conditions that can impose design limits on steel castings
3.answer.
The use of fibre reinforced composites has become increasingly attractive alternative to the conventional metals for many aircraft components mainly due to their increased strength durability, corrosion resistance, resistance to fatigue and damage tolerance characteristics Composites also provide greater flexibility because the material can be tailored to meet the design requirements and they also offer significant weight advantages. Carefully designed individual composite parts, at present, are about 20-30% lighter than their conventional metal counterparts. Although all-composite airplanes are now available in the world market, yet advances in the practical use of composite materials should enable further reduction in the structural weight of airplane. The composite materials used in aircraft industry are generally reinforced fibres or filaments embedded in a resin matrix. The most common fibres are carbon, aramid, glass and their hybrıd. The resın matrix is generally an epoxy based system requiring curing temperatures between 120° and 180°C (250° and 350°F) The first structural composite aircraft components, which were introduced during 1950-60, were made from glass fibre reinforced plastics. These components included the fin and the rudder of Grumman E-2A, helicopter canopies, frames, radomes, fairings, rotor blades, etc. Due to high strength and stiffness combined with low density, composites like Boron Fibre Reinforced Plastics (BFRP) and Carbon Fibre Reinforced Plastics (CFRP) .were preferred instead of aluminium for high performance aircraft structures. For lightly loaded structures, Aramid Fibre Reinforced Plastics (AFRP) which possess low density, have been used. The use of AFRP

continues to be restricted to the lightly loaded structures due to the fact that although these fibres possess high tensile strength, they have very low compressive strength. For light aircraft and lightly loaded structural components, Glass Fibre Reinforced Plastics (GFRP) has become one of the standard materials. Over the years, use of composite materials has also increased from few small access panels and canopy frames to almost complete airframe surfaces thereby providing weight savings leading to improved performance, reduced drag and also improved durability and corrosion resistance. Consequently, now-a-days, composite materials like GFRP, CFRP and AFRP have become standard materials for flight control surfaces, engine cowlings, fairings, radomes, landing gear doors, floor panels, fan ducts, etc. in aircraft application Weight savings provided by composites vary considerably with the type of aircraft and component. Weight savings, in terms of composite weight fraction are shown in Figure M11.1 These tend to decrease as the overall composite weight fraction increases.