Discuss about the composite machining processes and their fr

Discuss about the composite machining processes and their free-edge effects on the composite structural failures. Also, mention about the free-edge effects on the mechanical properties of composites and possible mitigation methods (less than 1 page).

Solution

Composite materials are anisotropic in nature so thay are difficult to machine than metals. Also, they are nonhomogeneous and their reinforcing fires are very abrasive. During machining, defects are induced into the work piece, and tools wear very rapidly. Conventional machining techniques such as drilling or sawing are used with proper tool design and operating conditions.

Drilling is the most common composite machining operation. During drilling of composites delamination of the top layer can also be produced by high thermal stresses generated by drilling, but, in that case, no discontinuities are observed in the normal force history. Delamination near the exit sides is introduced when the tool acts like a punch separating the thin uncut layer from the remainder of the laminate. This action is associated with an almost instant drop in normal force from its steady value down to zero. Fiber pull out can also happen.

Damage are introduced during the drilling operations: matrix cratering and thermal alteration, fiber pullout and fuzzing, interlaminate cracks and delamination, in addition to geometrical defects.

Free-edge stress fields decays rapidly away from the laminate edges.

The free edge effects are due to discontinuous change of elastic material properties in the adjacent layers of the laminate. The development of interlaminar stresses near the free edges has been shown with the help of cross-ply symmetric laminates.the deviations of the ply stresses from the homogeneous plate solution of in-plane stresses around holes contribute to the interlaminar effects