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An insight of the dominant fracture mechanisms occurring in mechanical metallic components during industrial service conditions is offered through this short overview. Emphasis is given on the phenomenological aspects of fracture and their relationships with the emergent fracture mode(s) with respect to the prevailed operating parameters and loading conditions. This presentation is basically fulfilled by embracing and reviewing industrial case histories addressed from a technical expert viewpoint. The referenced case histories reflected mainly the author's team expertise in failure analysis investigation. As a secondary perspective of the current study, selected failure investigation and prevention methodological approaches are briefly summarized and discussed, aiming to provide a holistic overview of the specific frameworks and systems in place, which could assist the organization of risk minimization and quality enhancement.

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Machinable brasses are a broad class of high strength copper-zinc alloys mainly containing lead to improve machinability. Conventional leaded brasses are widely used in several manufacturing sectors (i.e., fabrication of hydraulic components, fittings, valves, etc.) due to their superior workability in extrusion and drawing, together with their superior machinability for high efficiency production of final components in high speed/high precision machining centers. In addition to machinability, the mechanical behavior and general fracture mechanisms of these alloys are also important, due to their impact on the overall reliability and safety of brass components. In this study, the main fracture modes and mechanical characteristics of two industrial copper alloys, namely, CuZn39Pb3 and CuZn36Pb2As, are presented in relation to their microstructure. Optical metallography, macro-and microfractography, together with static and dynamic mechanical testing, were used as the principal analytical techniques for the present investigation.

The machinability in turning mode of three lead-free brass alloys, CuZn42 (CW510L), CuZn38As (CW511L) and CuZn36 (C27450) was evaluated in comparison with a reference free-cutting leaded brass CuZn39Pb3 (CW614N), as far as the quality characteristics, i.e., cutting force and surface roughness, were concerned. A design of experiments (DOE) technique, according to the Taguchi L 16 orthogonal array (OA) methodology, as well as analysis of variance (ANOVA) were employed in order to identify the critical-to-machinability parameters and to obtain their optimum values for high-performance machining. The experimental design consisted of four factors (cutting speed, depth of cut, feed rate and alloy) with four levels for each factor using the "smaller-the-better" criterion for quality characteristics' optimization. The data means and signal-to-noise (S/N) responses indicated that the depth of cut and the feed rate were the most influential factors for the cutting force and surface roughness, respectively. The optimized machining parameters for cutting force (34.59 N) and surface roughness (1.22 µm) minimization were determined. Confirmation experiments (cutting force: 39.37 N and surface roughness: 1.71 µm) seem to show that they are in close agreement to the main conclusions, thereby validating the findings of the statistical evaluation performed.

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