TEST BANK FOR Mechanical Design of Machine Elements and Machines A Failure Prevention Perspective 2nd Edition By Jack A. Collins, Henry R. Busby, George H. Staab

Exam (elaborations) TEST BANK FOR Mechanical Design of Machine Elements and Machines A Failure Prevention Perspective 2nd Edition By Jack A. Collins, Henry R. Busby, George H. Staab Chapter 1 1-1. Define engineering design and elaborate on each important concept in the definition. ------------------------------------------------------------------------------------------------------------------------------------- Solution (Ref. 1.2) Engineering design is an iterative decision-making process that has the objective of creating and optimizing a new or improved engineering system or device for the fulfillment of a human need or desire, with regard for conservation of resources and environmental impact. The essence of engineering (especially mechanical design) is the fulfillment of human needs and desires. Whether a designer is creating a new device of improving an existing design, the objective is always to provide the “best”, or “optimum” combination of materials and geometry. Unfortunately, an absolute optimum can rarely be achieved because the criteria of performance, life, weight, cost, etc. typically place counter-opposing demands upon any proposed combination of material and geometry. Designers must not only compete in the marketplace, but must respond to the clear and growing obligation of the global technical community to conserve resources and preserve the environment. Finally, iteration, or cut-and-try pervades design methodology. Selection of the best material and geometry are typically completed through a series of iterations. 2 1-2. List several factors that might be used to judge how well a proposed design meets its specified objectives. ---------------------------------------------------------------------------------------------------------------------------------- Solution (Ref. 1.3) The following factors might be used: (1) Ability of parts to transmit required forces and moments. (2) Operation without failure for prescribed design life. (3) Inspectability of potential critical points without disassembly. (4) Ability of machine to operate without binding or interference between parts. (5) Ease of manufacture and assembly. (6) Initial and life-cycle costs. (7) Weight of device and space occupied. (8) Ability to service and maintain. (9) Reliability, safety, and cost competitiveness. 3 1.3 Define the term optimum design, and briefly explain why it is difficult to achieve an optimum solution to a practical design problem. --------------------------------------------------------------------------------------------------------------------------------------- Solution A dictionary definition of adequate is “sufficient for a specified requirement”, and for the word optimum is “greatest degree attainable under implied or specified conditions”. In a machine design context, adequate design may therefore be defined as the selection of material and geometry for a machine element that satisfies all of its specified functional requirements, while keeping any undesirable effects within tolerable ranges. In the same context, optimal design may be defined as the selection of material and geometry for a machine element with specific the objective of maximizing the part’s ability to address the most significant functional requirements, making sure that all other functional requirements are adequately satisfied, and that any undesirable effects are kept within tolerable ranges. Optimum design of real mechanical elements is complicated by the need to study relationships between and among functions that embody many variables such as performance, life, weight, cost, and safety. Unfortunately, these variables place counter-opposing demands upon and selected combination of materials and geometry; design changes that improve the part’s ability to respond to one significant performance parameter may, at the same time, degrade its ability to respond to another important parameter. Thus, an absolute optimum design can rarely be achieved. 4 1-4. When to stop calculating and start building is an engineering judgment of critical importance. Write about 250 words discussing your views on what factors are important in making such a judgment. -------------------------------------------------------------------------------------------------------------------------------------- Solution The decision to stop calculating and start building is a crucial engineering responsibility. To meet design objectives, a designer must model the machine and each of its parts, make appropriate simplifying assumptions where needed, gather data, select materials, develop mathematical models, perform calculations, determine shapes and sizes, consider pertinent failure modes, evaluate results, and repeat the loop of actions just listed until a “best” design configuration is achieved. Questions always arise at each step in the design sequence. For example: (1) What assumptions should be made, how many, how detailed, how refined? (2) Are data available on loading spectra, environmental conditions, user practice, or must testing be conducted? (3) Are materials data available for the failure modes and operating conditions that pertain, and where are the data, or must testing be conducted? (4) What types of modeling and calculation techniques should be used; standard or special, closed-form or numerical, P-C, workstation, or supercomputer? (5) How important are reliability, safety, manufacturing, and/or maintainability? (6) What is the competition in the marketplace for producing this product? Often, the tendency of an inexperienced new engineer is to model, analyze, calculate, and refine too much, too often, and too long, loosing market niche or market share as a consequence. On the other hand, the “old-timer” in the design department often tends to avoid the analysis and build the product “right away”, risking unforeseen problems in performance, safety, reliability, or manufacturability at high cost. Although dependent upon the product and the application, the engineering decision to stop calculating and start building is always crucial to success. 5 1-5. The stages of design activity have been proposed in 1.6 to include preliminary design, intermediate design, detail design, and development and field service. Write a two- or three-sentence descriptive summary of the essence of each of these four stages of design. ------------------------------------------------------------------------------------------------------------------------------------- Solution (1) Preliminary design is primarily concerned with synthesis, evaluation, and comparison of proposed machine or system concepts. The result of the preliminary design stage is the proposal of a likelysuccessful concept to be designed in depth to meet specific criteria of performance, life, weight, cost, safety, or other aspects of the overall project. (2) Intermediate design embodies the spectrum of in depth engineering design of individual components and subsystems for the already pre-selected machine or system. The result of the intermediate design stage is the establishment of all critical specifications relating to function, manufacturing, inspection, maintenance, and safety. (3) Detail design is concerned mainly with configuration, arrangement, form, dimensional compatibility and completeness, fits and tolerances, meeting specifications, joints, attachment and retention details, fabrication methods, assemblability, productibility, inspectability, maintainability, safety, and estaqblishing bills of material and purchased parts. The result of the detail design stage is a complete set of working drawings and specifications, approved for production of a prototype machine. (4) Development and field service activities include development of a prototype into a production model, and following the product into the field, maintaining and analyzing records of failure, maintenance procedures, safety problems, or other performance problems. 6 1-6. What conditions must be met to guarantee a reliability of 100 percent? ----------------------------------------------------------------------------------------------------------------------------------- Solution A designer must recognize at the outset that there is no way to specify a set of conditions that will guarantee a reliability of 100%. There will always be a finite probability of failure. 7 1-7. Distinguish between fail safe design and safe life design, and explain the concept of inspectability, upon which they both depend. ------------------------------------------------------------------------------------------------------------------------------------------- Solution (Ref 1.5) Fail safe design is implemented by providing redundant load paths in a structure so that if failure of a primary structural member occurs, a secondary member is capable of carrying the load on an emergency basis until the primary structural failure is detected and repaired. Safe life design is implemented by carefully selecting a large enough safety factor and establishing inspection intervals to assure that the stress levels, the potential flaw size, and the governing failure strength levels combine to give crack growth rate slow enough to assure crack detection before the crack reaches its critical size. Both fail safe and safe life design depend on regularly scheduled inspections of all potential critical points. This implies that critical point locations must be identified, unfettered inspection access to the critical points must be designed into the structure from the beginning (inspectability), appropriate inspection intervals must be established (usually on a statistical basis), and a schedule must be established and executed to assure proper and timely inspections. 8 1-8. Iteration often plays a very important role in determining the material, shape, and size of a proposed machine part. Briefly explain the concept of iteration, and give an example of a design scenario that may require an iterative process to find a solution. ------------------------------------------------------------------------------------------------------------------------------------------- Solution A dictionary definition of iteration is “to do again and again.” In he mechanical design context, this may imply the initial selection of a material, shape, and size for a machine part, with the “hope” that functional performance specifications can be met and that strength, life, and safety goals will, at the same time be achieved. Then, examining the “hope” through the use of applicable engineering models, make changes in the initial selection of material, shape or size that will improve the part’s ability to meet the specified goals, and repeat the process (iterate) until the goals are met. For example, assume a stepped shaft needs to be designed for a newly proposed machine. Neither the material, the shape, nor the size are known at the outset. The loads, torques, speed, and bearing support locations are initially known. The iteration steps for such a case might include: (1) Select (assume) a potential material. (2) Establish a coordinate system and make a stick-sketch free-body diagram of the shaft, showing all known forces and moment and their locations. (3) Make a first-iteration conceptual sketch of the proposed shaft. (4) Using appropriate shaft design equations, calculate tentative diameters for each stepped section of the shaft. (5) By incorporating basic guidelines for creating shape and size, transform the first-iteration sketch into a more detailed second-iteration sketch that includes transition geometry from one step to another, shoulders, fillets, and other features. (6) Analyze the second-iteration shaft making appropriate changes (iterations) in material (to meet specified strength, stiffness, or corrosion resistance specifications), changes in shape (to alleviate stress concentrations, reduce weight, or provide for component retention), and changes in size (to reduce stress or deflection, or eliminate interference). (7) Continue iterations until a satisfactory design configuration has been achieved A more specific example of the design iteration process is discussed in Example 8-1. 9 1-9. Write a short paragraph defining the term “simultaneous engineering” or “concurrent engineering”. ------------------------------------------------------------------------------------------------------------------------------- Solution “Simultaneous” , or “concurrent” engineering is a technique for organizing and displaying information and knowledge about all design-related issues during the life cycle of a product, from the time marketing goals are established to the time the product is shipped. The technique depends upon an iterative computer system that allows on-line review and rapid update of the current design configuration by any member of the product design team, at any time, giving “simultaneous” access to the most current design configuration to all members. Properly executed, this approach prevents the need for costly “re-designs” by incorporating requirements of down-stream processes early in the preliminary design stage. 10 1-10. Briefly describe the nature of codes and standards, and summarize the circumstances under which their use should be considered by a designer. ------------------------------------------------------------------------------------------------------------------------------------- Solution (Ref. 1.9) Codes are usually legally binding documents, compiled by a governing agency, that are aimed at protecting the general welfare of its constituents and preventing loss of life, injury, or property damage. Codes tell the user what to do and when to do it. Standards are consensus-based documents, formulated through a cooperative effort among industrial organizations and other interested parties, that define good practices in a particular field. Standards are usually regarded as recommendations to the user for how to do the task covered by the standard. A designer should consider using applicable codes and standards in every case. If codes are not adhered to, a designer and their company may be exposed to litigation. If standards are not used, cost penalties, lack of interchangeability, and loss of market share may result and overall performance may be compromised as well. 11 1-11. Define what is meant be ethics in the field of engineering. --------------------------------------------------------------------------------------------------------------------------------- Solution Ethics and morality are formulations of what we ought to do and how we ought to behave, as we practice engineering. Engineering designers have a special responsibility for ethical behavior because the health and welfare of the public often hangs on the quality, reliability, and safety of their designs. 12 1-12. Explain what is meant by an ethical dilemma. ---------------------------------------------------------------------------------------------------------------------------------------- Solution An ethical dilemma is a situation that exists whenever moral reasons or considerations can be offered to support two or more opposing courses of action. An ethical dilemma is different from an ethical issue, which is a general scenario involving moral principles. 13 1-13.34 A young engineer, having worked in a multinational engineering company for about five years, has been assigned the task of negotiating a large construction contract with a country where it is generally accepted business practice, and totally legal under the country’s laws, to give substantial gifts to government officials in order to obtain contracts. In fact, without such a gift, contracts are rarely awarded. This presents an ethical dilemma for the young engineer because the practice is illegal in the United States, and clearly violates the NSPE Code of Ethics for Engineers [see Code Section 5(b) documented in the appendix]. The dilemma is that while the gift-giving practice is unacceptable and illegal in the United States, it is totally proper and legal in the country seeking the services. A friend, who works for a different firm doing business is the same country, suggests that the dilemma may be solved by subcontracting with a local firm based in the country, and letting the local firm handle gift giving. He reasoned that he and his company were not party to the practice of gift giving, and therefore were not acting unethically. The local firm was acting ethically as well, since they were abiding by the practices and laws of hat country. Is this a way out of the dilemma? ------------------------------------------------------------------------------------------------------------------------------------------- Solution This appears to be exactly what some U.S. firms do on a routine basis. If you think it is a solution to the ethical dilemma posed, reexamine section 5 (b) of the NSPE Code shown in the appendix. It begins, “Engineers shall not offer, give, solicit, or receive, either directly or indirectly, ….”. Clearly, the use of a subcontractor in the proposed manner is indirectly giving the gift. The practice is not ethical. 14 1-14.35 Two young engineering graduate students received their Ph.D. degrees from a major university at about the same time. Both sought faculty positions elsewhere, and they were successful in receiving faculty appointments at two different major universities. Both knew that to receive tenure they would be required to author articles for publication in scholarly and technical journals. Engineer A, while a graduate student, had developed a research paper that was never published, but he believed that it would form a sound basis for an excellent journal article. He discussed his idea with his friend, Engineer B, and they agreed to collaborate in developing the article. Engineer A, the principal author, rewrote the earlier paper, bringing it up to date. Engineer B’s contributions were minimal. Engineer A agreed to include Engineer B’s name as co-author of the article as a favor in order to enhance Engineer B’s chances of obtaining tenure. The article was ultimately accepter and published in a referred journal. a. Was it ethical for Engineer B to accept credit for development of the article? b. Was it ethical for Engineer A to include Engineer B as co-author of the article? --------------------------------------------------------------------------------------------------------------------------------------- Solution (a) Although young faculty members are typically placed under great pressure to “publish or perish”, Engineer B’s contribution to the article is stated to be minimal, and therefore seeking credit for an article that they did not author tends to deceive the faculty tenure committee charged with the responsibility of reviewing his professional progress. Section III.3.C of the Code (see appendix) reads, in part, “… such articles shall not imply credit to the author for work performed by others.” Thus, accepting co-authorship of the paper, to which his contribution was minimal, is at odds with academic honesty, professional integrity, and the Code of Ethics . Engineer B’s action in doing so is not ethical. (b) Engineer A’s agreement to include Engineer B as co-author as a favor, in order to enhance Engineer B’s chances of obtaining tenure, compromises Engineer A’s honesty and integrity. He is professionally diminished by this action. Collaborative efforts should produce a high quality product worthy of joint authorship, and should not merely be a means by which engineering faculty expand their list of achievements. Engineer A’s action is not ethical. 15 1-15. If you were given the responsibility for calculating the stresses in a newly proposed “Mars Lander,” what system of units would you probably choose? Explain. ----------------------------------------------------------------------------------------------------------------------------------------- Solution The best choice would be an absolute system of units, such as the SI system. Because the mass is the base unit and not dependent upon local gravity. 16 1-16. Explain hoe the lessons-learned strategy might be applied to the NASA mission failure experienced while attempting to land the Mars Climate Orbiter on the Martian surface in September 1999. The failure event is briefly described in footnote 31 to the first paragraph of 1.14. ----------------------------------------------------------------------------------------------------------------------------------------- Solution As noted in footnote 31, the mission failure was caused by poor communication between two separate engineering teams, each involved in determining the spacecraft’s course. One team was using U.S units and the other team was using metric units. Apparently units were omitted from the numerical data, errors were made in assuming what system of units should be associated with the data, and, as a result, data in U.S. units were substituted directly into metric-based thrust equations, later embedded in the orbiter’s guidance software. As discussed in 1.7, the lessons-learned strategy may be implemented by making an organized effort to observe inaction procedures, analyze them in after-action reviews, distill the reviews into lessons learned, and disseminate the lessons learned so the same mistakes are not repeated. In the case of the Mars Climate Orbiter, little effort was required to define the overall problem: the Orbiter was lost. A review by NASA resulted in discovery of the incomplete units used in performing the Orbiter’s guidance software. A proper next curse of action would be to define ways of reducing or preventing the possibility of using inconsistent units in making performance calculations. Perhaps by a requirement to always attach units explicitly to numerical data. Perhaps by an agreement that would bind all parties to use of a single agreed-upon system of units. Perhaps by mandating an independent quality assurance review of all inter-group data transmission. Whatever remedial actions are decided upon, to be effective, must be conveyed to all groups involved, and others that may be vulnerable to error caused by the use of inconsistent units. 17 1-17. A special payload package is to be delivered to the surface of the moon. A prototype of the package, developed, constructed, and tested near Boston, has been determined to have a mass of 23.4 kg. a. Estimate the weight of the package in newtons, as measured near Boston. b. Estimate the weight of the package in newtons on the surface of the moon, if gmoon = 17.0 m/s2 at the landing site. c. Reexpress the weights in pounds. ---------------------------------------------------------------------------------------------------------------------------------------- Solution The weight of the package near Boston and on the moon are (23.4 kg)(9.81 m/s2 ) 229.6 N 229.6 N 51.6 lb Boston 4.448 N/lb W = F = ma = = = = (23.4 kg)(1.70 m/s2 ) 39.8 N 39.8 N 8.95 lb moon 4.448 N/lb W = F = ma = = = = 18 1-18. Laboratory crash tests of automobiles occupied by instrumented anthropomorphic dummies are routinely conducted by the automotive industry. If you were assigned the task of estimating the force in newtons at the mass center of the dummy, assuming it to be a rigid body, what would be your force prediction if a head-on crash deceleration pulse of 60 g’s (g’s are multiples of the standard acceleration of gravity) is to be applied to the dummy? The nominal weight of the dummy is 150 pounds. ------------------------------------------------------------------------------------------------------------------------------- Solution ( )( ) 2 150 lb 4.448 N/lb 68 kg 9.81 m/s m W g = = = F = ma = (68 kg)(9.81 m/s2 -g)(60 g) = 40 kN 19 1-19. Convert a shaft diameter of 2.25 inches into mm. ----------------------------------------------------------------------------------------------------------------------------------- Solution Ds = 2.25 in (25.4 mm/in) = 57.2 mm 20 1-20. Convert a gear-reducer input torque of 20,000 in-lb to N-m. -------------------------------------------------------------------------------------------------------------------------------- Solution (20,000 in-lb) 0.1138 N-m 2276 N-m g in-b T = ⎛ ⎞ = ⎜ ⎟ ⎝ ⎠ 21 1-21. Convert a tensile bending stress of 869 MPa to psi. --------------------------------------------------------------------------------------------------------------------------------- Solution 3 (876 MPa) 1 psi 127,050 psi 6.895 10 MPa σ b − = ⎛ ⎞ ≈ ⎜ × ⎟ ⎝ ⎠ 22 1-22. It is being proposed to use a standard W10× 45 (wide-flange) section for each of four column supports for an elevated holding tank. (See Appendix Table A.3 for symbol interpretation and section properties.) What would be the cross-sectional area in mm2 of such a column cross section? --------------------------------------------------------------------------------------------------------------------------------- Solution Using Appending Table A-3 and Table 1.4 2 2 2 2 (13.3 in ) 645.16 mm 8580.6 mm in AW ⎛ ⎞ = ⎜⎜ ⎟⎟ = ⎝ ⎠ 23 1-23. What is the smallest standard equal-leg angle-section that would have a cross-sectional area at least as large as the W10× 45 section of problem 1-22? (From Table A.3, theW10× 45 section has a cross-sectional area of 13.3 in2 .) ------------------------------------------------------------------------------------------------------------------------------------- Solution For a W10× 45 , A = 13.3 in2 . From Appendix Table A-6, the minimum area, AL , for a structural equal-leg angle section requires that nothing smaller than 1 8 8 18 L × × be used. 24 Chapter 2 2-1. In the context of machine design, explain what is meant by the terms failure and failure mode. --------------------------------------------------------------------------------------------------------------------------- Solution Mechanical failure may be defined as any change in the size, shape, or material properties of a structure, machine, or machine part that renders it incapable of satisfactorily performing its intended function. Failure mode may be defined as the physical process or processes that take place or combine their effects to produce failure. 25 2-2. Distinguish the difference between high-cycle fatigue and low-cycle fatigue, giving the characteristics of each. --------------------------------------------------------------------------------------------------------------------------- Solution High-cycle fatigue is the domain of cyclic loading for which strain cycles are largely elastic, stresses relatively low, and cyclic lives are long. Low-cycle fatigue is the domain of cyclic loading for which strain cycles have a significant plastic component, stresses are relatively high, and cyclic lives are short. 26 2-3. Describe the usual consequences of surface fatigue. --------------------------------------------------------------------------------------------------------------------------- Solution Surface Fatigue is as failure phenomenon usually resulting from rolling surfaces in contact, in which cracking, pitting, and spalling occur. The cyclic Hertz contact stresses induce subsurface cyclic shearing stresses that initiate subsurface fatigue nuclei. Subsequently, the fatigue nuclei propagate, first parallel to the surface then direct to the surface to produce dislodged particles and surface pits. The operational results may include vibration, noise, and/or heat generation. This failure mode is common in bearings, gear teeth, cams, and other similar applications. 27 2-4. Compare and contrast ductile rupture and brittle fracture. --------------------------------------------------------------------------------------------------------------------------- Solution Brittle Fracture manifests itself as the very rapid propagation of a crack, causing separation of the stressed body into two or more pieces after little or no plastic deformation. In polycrystalline metals the fracture proceeds along cleavage planes within each crystal, giving the fracture surface a granular appearance. Ductile rupture, in contrast, takes place as a slowly developing separation following extensive plastic deformation. Ductile rupture proceeds by slow crack growth induced by the formation and coalescence of voids, giving a dull and fibrous appearance to the fracture surface. 28 2-5. Carefully define the terms creep, creep rupture, and stress rupture, citing the similarities that relate these three failure modes and the differences that distinguish them from one another. --------------------------------------------------------------------------------------------------------------------------- Solution Creep is the progressive accumulation of plastic strain, under stress, at elevated temperature, over a period of time. Creep Rupture is an extension of the creep process to the limiting condition where the part separates into two pieces. Stress Rupture is the rupture termination of a creep process in which steady-state creep has never been reached. 29 2-6. Give a definition for fretting, and distinguish among the related failure phenomena of fretting fatigue, fretting wear, and fretting corrosion. --------------------------------------------------------------------------------------------------------------------------- Solution Fretting is a combined mechanical and chemical action in which the contacting surfaces of two solid bodies are pressed together by a normal force and are caused to execute oscillatory sliding relative motion, wherein the magnitude of normal force is great enough and the amplitude of oscillatory motion is small enough to significantly restrict the flow of fretting debris away from the originating site. Related failure phenomena include accelerated fatigue failure, called Fretting-Fatigue, loss of proper fit or significant change in dimensions, called Fretting wear, and corrosive surface damage, called Fretting-corrosion. 30 2-7. Give a definition of wear failure and list the major subcategories of wear. --------------------------------------------------------------------------------------------------------------------------- Solution Wear failure may be defined as the undesired cumulative change in dimensions brought about by the gradual removal of discrete particles from contacting surfaces in motion (usually sliding) until dimensional changes interfere with the ability of the part to satisfactorily perform its intended function. The major subcategories of wear are: (a) Adhesive wear (d) Surface fatigue wear (g) Impact wear (b) Abrasive wear (e) Deformation wear (c) Corrosive wear (f) Fretting wear 31 2-8. Give a definition for corrosion failure, and list the major subcategories of corrosion. --------------------------------------------------------------------------------------------------------------------------- Solution Corrosion failure is said to occur when a machine part is rendered incapable of performing its intended function because of the undesired deterioration of a material through chemical or electrochemical interaction with the environment, or destruction of materials by means other than purely mechanical action. The major subcategories of corrosion are: (a) Direct chemical attack (e) Intergranular corrosion (i) Hydrogen damage (b) Galvanic corrosion (f) Selective leaching (j) Biological corrosion (c) Crevice corrosion (g) Erosion corrosion (k) Stress corrosion cracking (d) Pitting corrosion (h) Cavitation corrosion 32 2-9. Describe what is meant by a synergistic failure mode, give three examples, and for each example describe how synergistic interaction proceeds. --------------------------------------------------------------------------------------------------------------------------- Solution Synergistic failure modes are characterized as a combination of different failure modes which result in a failure more serious than that associated with either constituent failure mode. Three examples are 1. Corrosion wear; a combination failure mode in which the hard, abrasive corrosion product accelerates wear, and the wear-removal of “protective” corrosion layers tends to accelerate corrosion. 2. Corrosion Fatigue; a combination failure mode in which corrosion-produced surface pits and fissures act as stress raisers that accelerate fatigue, and the cyclic strains tend to “crack” the brittle corrosion layers to allow a to atmospheric penetration and accelerated rates of corrosion. 3. Combined Creep and Fatigue; a combination failure mode in which details of the synergistic interaction are not well understood but data support the premise that the failure mode is synergistic. 33 2-10. Taking a passenger automobile as an example of an engineering system, list all failure modes you think might be significant, and indicate where in the auto you think each failure mode might be active. --------------------------------------------------------------------------------------------------------------------------- Solution A list of potential failure modes, with possible locations might include, but not be limited to Possible Failure Mode Possible Location Brinnelling Bearings, cams. gears High-cycle fatigue Connecting rods, shafts, gears, springs, belts Impact fatigue Cylinder heads, valve seats, shock absorbers Surface fatigue Bearings, cams, gears Corrosion fatigue Springs, driveshaft Fretting fatigue Universal joints, bearing pads, rocker arm bearings Direct chemical attack (corrosion) Body panels, frame, suspension components Crevice corrosion Body panels, joints, frame joints Cavitation corrosion Water pump Adhesive wear Piston rings, valve lifters, bearings, cams, gears, brakes Corrosion-wear Brakes, suspension components Fretting wear Universal joints, rocker arm bearings Thermal relaxation Engine head bolts, exhaust manifold bolts Galling seizure Nuts on bolts, piston rings, bearings, valve guides, hinges Buckling Body panels, hood, springs 34 2-11. For each of the following applications, list three of the more likely failure modes, describing why each might be expected: (high-performance automotive racing engine, (b) pressure vessel for commercial power plant, (c) domestic washing machine, (d) rotary lawn mower, (e) manure spreader, (f) 15-inch oscillating fan. --------------------------------------------------------------------------------------------------------------------------- Solution (a) High-performance automotive engine: 1. High cycle fatigue; high speed, high force, light weight. 2. Adhesive wear; high sliding velocity, high contact pressure, and elevated temperature. 3. Galling and seizure; high sliding velocity, high contact pressure, elevated temperature, potential lubricant breakdown. (b) Pressure vessel for commercial power plant: 1. Thermal relaxation; closure bolts lose preload to violate pressure seal. 2. Stress corrosion; impurities in feed water, elevated temperature and pressure. 3. Brittle fracture; thick sections, high pressure, growing flaw size due to stress corrosion cracking. (c) Domestic washing machine: 1. Surface fatigue; gear teeth, heavy loading, potential impact, many cycles. 2. Direct chemical attack (corrosion); lubricants attack seals and belts, detergent-bearing water may infiltrate bearings. 3. Impact fatigue; spin-cycle imbalance induces impact, many cycles (d) Rotating lawn mowers: 1. Impact deformation; high rotary blade speed, objects in blade path. 2. Yielding; high rotary blade speed, immovable object in blade path. 3. High cycle fatigue; high speed, many cycles (e) Manure spreader: 1. Direct chemical attack (corrosion); corrosive fluids and semisolids of barnyard manure, exposed and constantly abraded surfaces of transport chains, slats, distribution augers, beaters, and supports. 2. Abrasive wear; mixture of manure, dirt and sand, constant sliding between mixture and surfaces, minimal lubrication. 3. High-cycle fatigue; high speeds, many cycles (f) Fifteen-inch oscillation electric fan: 1. Adhesive/abrasive wear; minimal lubrication, high rotary bearing speed, many cycles 2. Force-induced elastic deformation; rotary blade elastic deformation. 3. Impact wear; reversing drive linkage, high forces, many cycles. 35 2-12. In a tension test of a steel specimen having a 6-mm-by-23-