材料選擇外文文獻翻譯、中英文翻譯

1、附譯文二Selecting MaterialsWe are surrounded by materials and we rarely think about how thesematerials are selected. Why was your desk made of solid wood, plywood, orplastic-laminated particleboard? Why have so many plastics replaced steel andzinc in automobiles? What is the controversy about using foam

2、ed polystyreneplastic to package fast food?While you might take granted the materials that make up your products,you can be sure that the designers did not. People who design homes, cars,aircraft, clothing, furniture, and other products or systems devote a lot ofattention to the selection of the mat

3、erials they use. Material selection might makeor break a company. But how do the designers make that selection to arrive atthe best material? What selection criteria are most important?The Ideal MaterialWhat is an ideal material? Among other characteristics, we can list thefollowing for the ideal ma

4、terial:1. Endless and readily available source of supply2. Cheap to refine and produce3. Energy efficient4. strong, stiff, and dimensionally stable at all temperatures5. Lighweight6. Corrosion resistant7. No harmful effects on the environment or people8. Biodegradable9. Numerous secondary usesIt is

5、a very complex process for the designer to find the ideal material for aspecific product.Obstacles to ChangeSwitching from traditional materials such as steel and concrete to newermaterials such as plastic-based composites seem a simple, straightforwardapproach for the contemporary designer. The new

6、er materials are often superior,but sometimes there are complications. Often, lack of experience with newmaterials causes hesitation by designers. Departures from tried-and-truematerials may be costly. It requires time before both designers and fabricatorsgain sufficient experience to make products

7、or systems. This problem isexacerbated when human life might be in jeopardy, such as when designing foraircraft. Consequently, new materials and processes are usually slower to enterthe marketplace than might be expected. These issues are all a part ofengineering problem solving. Materials selection

8、 is a problem-solving issue thatrequires an algorithm for its solution.Algorithm for Materials SelectionEngineering requires clearly stated, unambiguous steps for problem solving.Algorithms are well-defined methods for solving specific problems. Computerprograms are written after an algorithm has be

9、en developed to lie out clearly thesteps that the program is to solve. For example, you could write a simplealgorithm to calculate the strength required of a light pole to withstand thepushing forces from a light fixture. A much more complex algorithm would berequired to select a piston connecting r

10、od for an internal-combustion engine. Thefirst problem requires only the selection of a material of suitable size/strength tohold up the light fixture, and almost any material would suffice as long as it wassufficiently strong and pleasing to the user. On the other hand, a connecting rodwill undergo

11、 many types of mechanical stress, ranging from compressive totensile to torsional to gravity forces, in addition to thermal stress from thecombustion chamber. How does the designer match component requirementswith available materials?Selection ToolsTo aid in the creation of materials selectionalgori

12、thms, databases must be available to answer questions on materialsuitability. A materials database involves tables listing properties of materials,such as tensile strength, hardness, corrosion resistance, and the ability towithstand heat. Thousands of reference books are available with such data.Muc

13、h of these data are computerized to allow easier access. Certain graphicaltechniques aid the designer in materials selection.Properties of MaterialsPeriodicals can provide current data andperformance criteria that involve that involve structural materials:1. Strength (tensile, compressive, flexural,

14、 shear, and torsional)2. Resistance to elevated temperatures3. Fatigue resistance (repeated loading and unloading)4. Toughness (resistance to impact)5. Wear resistance (harddness)6. Corrosion resistanceSuch publications present values for the performance criteria (properties)for metals, polymers, an

15、d ceramics, with updates on newer materials such asaramid fibers, zinc aluminum alloys, and super alloys. Various periodicals haveannual materials selectors that provide general information on properties for along list of materials.The many tables, covering representative materials, provide general

16、data onproperties for a simple comparison. Selection of specific materials requires manymore detailed specifications. General databases from handbooks will providemuch detail, but the final selection often requires that material manufacturerssupply their own properties database for their product lin

17、es. While databases areimperative in the initial selection steps, there are other factors that complicatematerials selection.Materials SystemsMaterials rarely exist in isolation withoutinteracting with other materials. Rather, a combination of materials is selected tocomplement one another. In a suc

18、cessful materials system, each component iscompatible with the others while contributing its distinctive properties to theoverall characteristics of the system of which it is a part. A state-of-the arttelephone is a good example. The casing might be a tough ABS plastic, whichhouses a microchip (a so

19、lid-state ceramic device) that provides memory andsound-transmission capabilities. Copper leads join the circuitry together. Theremight be a battery and a ceramic must light-emitting diode to show when thebattery is low. The acid in the battery must be isolated to prevent corrosion, andthe copper le

20、ads must be insulated so that they do not short out. Each componentis made of materials that meet the demands of the physical and chemicalenvironment normally encountered when using the system.Additional Selection CriteriaExisting specifications have a lot ofinfluence on the choice of material. Thes

21、e specifications or “standards” are usedwhen redesigning an improved model of the product. When thematerials-selection algorithm results in selection of a new material, I might notbe covered by current specifications from standardization agencies. Theconditions of safety must be met by those involve

22、d in the manufacture or use ofgoods and services. It might take the new material or they might not approve itsuse.Availability is another concern of the designer. Will the material be easilyavailable in the quantities and sizes required by the production demands? Inaddition, will it be available in

23、the shapes required? Aluminum extrusions, forexample, are available in many varieties of standard shapes, such as round, oval,and square tubing. In the past, designers were limited to existing materials suchas metal alloys, woods, or concrete. Now, it is possible to start from scratch at thesynthesi

24、s stage to have materials engineers design a materials system to provideproperties to meet the expected needs.Processibility, the ease with which raw materials can be transformed into afinished product, is of paramount concern. Much of the current focus is onlow-energy processing. Companies may have

25、 difficulty processing the newmaterial on existing equipment. Can they afford to invest in new equipment?Today, the reverse question is usually asked: Can we afford to use the newmaterial and process? If we do not, the competition might make the change andrun us out of business with their superior p

26、roduct. Many new technologies arenow available.Quality and performance are two aspects that achieve consumer satisfaction.The high cost of most durable goods and the competition for customeracceptance has resulted in extended warranties. Materials selection must ensurethat parts will not rust, break

27、 under repeated stress, or fail to perform in anyother way for the predicted service life of the product.Consumer acceptance includes many factors beyond excellent quality andhigh performance; there are also societal aspects. Society as a whole as well asgovernmental agency is requiring a closer loo

28、k at manufactured products. Anyproduct has to be considered in terms of its total life cycle. What are the resultsof the processing methods? Are polluting gases being released into theenvironment, or are toxic metals and chemicals being flushed into our rivers andstreams? During use, does the produc

29、t safeguard our health? At the end of thes useful life, how can it be disposed of safely? Municipal solid waste is ahidden product cost that we pay in the form of higher taxes and poorer quality oflife. Fast-food restaurant chains moved away from polystyrene packages becausethe public felt these pla

30、stic containers were more harmful to the environmentthan paper packaging. Soft-drink manufacturers are moving toward reusableplastic bottles.Design for disassembly has become a theme in much of product design bymajor corporations. Europe, which has a higher degree of ecological concern, hasled the w

31、ay. With the desire to facilitate recycling, manufacturers of smallappliances and durable goods are establishing procedures to ensure thatproducts can be broken into components for easy sorting prior to recycling.Among the procedures are reducing the variety of plastics, adding labels toplastics for

32、 easy identification of plastic type, and eliminating screws andadhesives so that parts will disassemble easily.One of the latest software programs is designed specifically to makeproducts easier to fix. Known as Design for Service, this program takes its placealongside previous software programs ca

33、lled Design for Assembly and Design forManufacturability. This new program helps product designers consider repairissues early in the design stage. Objectives of the program include makingrepairs less costly and extending the functioning life of products. Environmentalissues such as recycling are di

34、rectly addressed by this new computer software,which may have customers fixing products rather than tossing them out. Inaddition, this software augments previous software that addresses the need fordisassembly of a product for whatever reason.More often than not, cost is the primary selection criter

35、ion that willdetermine the final choice of material. In other words, if several materials havethe specified physical, mechanical, and chemical properties, and are suitable forthe processing technique selected, the lower-cost materials would be the logicalchoice. Determining cost is not as simple as

36、it may seem. For example, a varietyof plastics, including PET (poly ethylene terephthalate) and HDPE (high-densitypolyethylene), have replaced glass as containers for soft drinks, milk and juices.Although the initial cost of plastic may be greater, the plastic bottles providesaving due to their toug

37、hness (less breakage) and the saving in shipping (PETand HDPE are much lighter than glass bottles).Product liability is civil (as opposed to criminal) liability of the manufacturer toan ultimate user for injury resulting from a defective product. Caveat emptor (letthe buyer beware) was once the rule. Today, numerous liability laws are in effect.For those involved in materials selection in the design process, the trend is forcourts and juries to identify members of the design team as being responsible forsome fault in a product-liability action. Therefore, it is impera