210 Budynas-Nisbett:Shigley's ll.Failure Prevention 5.Failures Resulting from T©The McGraw-Hill Mechanical Engineering Static Loading Companies,2008 Design,Eighth Edition 206 Mechanical Engineering Design In Chap.I we learned that strength is a property or characteristic of a mechanical element.This property results from the material identity,the treatment and processing incidental to creating its geometry,and the loading,and it is at the controlling or critical location. In addition to considering the strength of a single part,we must be cognizant that the strengths of the mass-produced parts will all be somewhat different from the others in the collection or ensemble because of variations in dimensions,machining, forming,and composition.Descriptors of strength are necessarily statistical in nature,involving parameters such as mean,standard deviations,and distributional identification. A static load is a stationary force or couple applied to a member.To be stationary, the force or couple must be unchanging in magnitude,point or points of application, and direction.A static load can produce axial tension or compression,a shear load,a bending load,a torsional load,or any combination of these.To be considered static,the load cannot change in any manner. In this chapter we consider the relations between strength and static loading in order to make the decisions concerning material and its treatment,fabrication,and geometry for satisfying the requirements of functionality,safety,reliability,competitiveness, usability,manufacturability,and marketability.How far we go down this list is related to the scope of the examples "Failure"is the first word in the chapter title.Failure can mean a part has sepa- rated into two or more pieces;has become permanently distorted,thus ruining its geometry:has had its reliability downgraded;or has had its function compromised, whatever the reason.A designer speaking of failure can mean any or all of these pos- sibilities.In this chapter our attention is focused on the predictability of permanent distortion or separation.In strength-sensitive situations the designer must separate mean stress and mean strength at the critical location sufficiently to accomplish his or her purposes. Figures 5-1 to 5-5 are photographs of several failed parts.The photographs exem- plify the need of the designer to be well-versed in failure prevention.Toward this end we shall consider one-,two-,and three-dimensional stress states,with and without stress concentrations,for both ductile and brittle materials. Figure 5-1 (a)Failure of a truck drive-shaft spline due to corrosion fatigue.Note that it was necessary to use clear tape to hold the pieces in place. (b)Direct end view of failure. (a)Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition II. Failure Prevention 5. Failures Resulting from Static Loading 210 © The McGraw−Hill Companies, 2008 206 Mechanical Engineering Design In Chap. 1 we learned that strength is a property or characteristic of a mechanical element. This property results from the material identity, the treatment and processing incidental to creating its geometry, and the loading, and it is at the controlling or critical location. In addition to considering the strength of a single part, we must be cognizant that the strengths of the mass-produced parts will all be somewhat different from the others in the collection or ensemble because of variations in dimensions, machining, forming, and composition. Descriptors of strength are necessarily statistical in nature, involving parameters such as mean, standard deviations, and distributional identification. A static load is a stationary force or couple applied to a member. To be stationary, the force or couple must be unchanging in magnitude, point or points of application, and direction. A static load can produce axial tension or compression, a shear load, a bending load, a torsional load, or any combination of these. To be considered static, the load cannot change in any manner. In this chapter we consider the relations between strength and static loading in order to make the decisions concerning material and its treatment, fabrication, and geometry for satisfying the requirements of functionality, safety, reliability, competitiveness, usability, manufacturability, and marketability. How far we go down this list is related to the scope of the examples. “Failure” is the first word in the chapter title. Failure can mean a part has sepa￾rated into two or more pieces; has become permanently distorted, thus ruining its geometry; has had its reliability downgraded; or has had its function compromised, whatever the reason. A designer speaking of failure can mean any or all of these pos￾sibilities. In this chapter our attention is focused on the predictability of permanent distortion or separation. In strength-sensitive situations the designer must separate mean stress and mean strength at the critical location sufficiently to accomplish his or her purposes. Figures 5–1 to 5–5 are photographs of several failed parts. The photographs exem￾plify the need of the designer to be well-versed in failure prevention. Toward this end we shall consider one-, two-, and three-dimensional stress states, with and without stress concentrations, for both ductile and brittle materials. Figure 5–1 (a) Failure of a truck drive-shaft spline due to corrosion fatigue. Note that it was necessary to use clear tape to hold the pieces in place. (b) Direct end view of failure