Practical and Engineering Approaches

RP products can often be designed and fabricated with very little or no stress analysis. Many parts, particularly URPs, are volume-filling products that carry only small stresses and only require a practical approach (Table 7.4). There is a cost disadvantage in performing any analysis 

The basic/simplified equations can be very restricted because of idealizations made in their deviations with regard to the simplicity of any material and the kinematics of the displacements. They are usually used in cases of intermediate difficulty, such as those for which some numerical guidance on internal stress is needed, or when the inherent simplicity of the part or the lack of any need for high precision indicates that relatively elementary analysis approaches are used. Stress analysis involves using the description of part geometry, applied loads and displacements, and material properties to obtain numerical expressions for internal stresses as a function of position in the part. 

There are different techniques that have been used for over a century to increase properties such as the modulus of elasticity (E) and moment of inertia (i) of products. Orientation or the use of fillers and/or reinforcements such as RPs can be used. There is also the popular and extensively used approach of using geometrical design shapes that makes the best use of materials to improve stiffness even for those that have a low modulus. Structural shapes that are applicable to all materials include shells, sandwich structures, and folded plate structures (Table 7.5). These widely used shapes employed include other shapes such as dimple sheet surfaces. They improve the flexural stiffness in one or more directions. 

In each example, displacing material from the neutral plane makes the improvement in flexural stiffness. This increases the El product that is the geometry material index that determines resistance to flexure. The El theory applies to all materials (plastics, metals, wood, etc.). It is the elementary mechanical engineering theory that demonstrates some shapes resist deformation from external loads. 

This phenomenon stems from the basic physical fact that deformation in beam or sheet sections depends upon the mathematical product of the E and 7, commonly expressed as El. This theory has been applied to many different plastic constructions including solid to different sandwich structures. 

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There are the practical and engineering approaches used to design products. Both have their important place in the world of design. With experience most products usually use the practical approach since they... 

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