Final answer:
Fastener threads are stronger in tension than in shear. It's generally better to position them to handle tensile loads, but they can be designed to withstand some shear forces depending on the application and design specifications. Engineers must consider load nature and design appropriately.
Step-by-step explanation:
The question of whether fastener threads should always be placed in shear or tension depends on the specific application and design requirements. Generally speaking, fastener threads are designed to be strongest in tension and weakest in shear. Therefore, whenever possible, it's preferable to position them such that the load is primarily in tension.
However, there are circumstances where fastener threads must endure shear forces, and although this is not ideal, threads can be designed to handle a certain amount of shear. This includes designing the joint with adequate thread engagement, appropriate fastener material, and considering the type of loading the joint will be subjected to. For example, in some cases, use of locking features or adhesives can help maintain the integrity of the joint under shear stress.
It's essential for engineers to closely adhere to design principles and consider the nature of the load when placing fasteners. Incorrect placement could lead to premature failure or reduced joint strength.