Influence of machining damage generated during trimming of CFRP composite on the compressive strength

Machining of composite materials is a challenging task due to the heterogeneity and anisotropy of composite structures. The induced defects reduce integrity of the machined surface as well as the loading capacity of the composite structure in service. Therefore, it is necessary to quantify the damage induced during trimming and correlate the quality of the machined surface to mechanical properties. The correlation of the surface roughness criteria, widely used in literature, to the mechanical behavior raise several contradictions. For this reason, new parameters for the characterization of the machined surface are proposed and correlated to the mechanical behavior under compressive loading. In this context, carbon fiber-reinforced plastic laminates are conventionally trimmed, and the machining damage is characterized using scanning electron microscope observations, X-ray tomography, and 3D optical topography. The results reveal that crater volume and maximum depth of damage quantify the machining damage more realistic compared to the classical surface roughness criteria.

Study on Machining Damage of Helical Milling for C/E Composites

Carbon fiber/epoxy resin composites (C/E composites) are wildly used in manufacture of aircraft fuselages and wings in aerospace industry, due to their excellent properties. However, hole making of C/E composites always results in machining damage, such as burr, tearing, delamination and so on. Milling tools with different shapes were used to conduct helical milling experiments on C/E composites. The influence of tool shape on machining damage was analyzed by measuring the damage area of burr, tearing and delamination. And then the feed speed, axial feed per orbital revolution and spindle speed was changed respectively to study the effect of processing parameters on machining damage. The machining damage can be reduced by choosing appropriate tool shape and processing parameters.

Unraveling the Age Hardening Response in U-Nb Alloys

Complicating factors that have stymied understanding of uranium-niobium’s aging response are briefly reviewed, including (1) niobium inhomogeneity, (2) machining damage effects on tensile properties, (3) early-time transients of ductility increase, and (4) the variety of phase transformations. A simple Logistic-Arrhenius model was applied to predict yield and ultimate tensile strengths and tensile elongation of U-4Nb as a function of thermal age. Fits to each model yielded an apparent activation energy that was compared with phase transformation mechanisms.