Lesson 11Lesson 11

Material SelectionMaterial Selection

During recent years the selection of engineering materials has assumed great importance. Moreover, the process should be one of continual reevaluation. New materials often become available and there may be a decreasing availability of others. Concerns regarding environmental pollution, recycling and worker health and safety often impose new constraints.

reevaluation重估计 , 重求值constraint n.约束 , 强制 , 局促RenewableSustainable

The desire for weight reduction or energy savings may dictate the use of different materials. Pressures from domestic and foreign competition, increased serviceability requirements, and customer feedback may all promote materials reevaluation. The extent of product liability actions, often the result of improper material use, has had a marked impact.

Dictate v. 口述 , 口授 , 指令 , 指示 , 命令 , 规定n. 指示 ( 指理智 ,变心 )dictator n.独裁者 , 独裁政权执政者dictatorship n.专政Serviceability n. 有用性 , 适用性 liability n.责任 , 义务 , 倾向 , 债务 , 负债

In addition, the interdependence between materials and their processing has become better recognized, the development of new processes often forces reevaluation of the materials being processed. Therefore, it is imperative that design and manufacturing engineers exercise considerable care in selecting, specifying, and utilizing materials if they are to achieve satisfactory results at reasonable cost and still assure quality.

In addition, also moreover, too besides, furthermore

therefore, hence consequently, as the result

Imperative n. 命令 , 需要 , 规则 , adj. 命令的 , 紧急的 , 必要的 , 势在必行的 ,

The first step in the manufacture of any product is design, which usually takes place in several distinct stages: (a) conceptual; (b)functional; (c)production design. During the conceptual-design stage, the designer is concerned primarily with the functions the product is to fulfill. Usually several concepts are visualized and considered, and a decision is made either that the idea is not practical or that the idea is sound and one or more of the conceptual designs should be developed further.

visualizevt. 形象 , 形象化想象fulfill vt.履行 , 实现 , 完成 ( 计划等 )

Here, the only concern for materials is that materials exist that can provide the desired properties. If no such materials are available, consideration is given as to whether there is a reasonable prospect that new ones could be developed within cost and time limitations.

prospectn. 景色 , 前景 , 前途 , 期望vi. 寻找 , 勘探

At the functional- or engineering-design stage, a practical, workable design is developed. Fairly complete drawings are made, and materials are selected and specified for the various components. Often a prototype or working model is made that can be tested to permit evaluation of the product as to function, reliability, appearance, serviceability, and so on.

fairly adv.公正地 , 正当的 , 公平地相当地 , 还算 , 清楚地prototype n.原型 , 样机appearance n.出现 , 露面外貌 , 外观

Although it is expected that such testing might show that some changes may have to be made in materials before the product is advanced to the production-design stage, this should not be taken as an excuse for not doing a thorough job of material selection. Appearance, cost, and reliability factors should be considered in detail, together with the functional factors.

Excuse vt.原谅 , 申辩 , 做为 ... 的托辞n. 饶恕 , 致歉 理由 , 口实 , 借口

There is much merit to the practice of one very successful company which requires that all prototypes be built with the same materials that will be used in production and, insofar as possible, with the same manufacturing techniques. It is of little value to have a perfectly functioning prototype that cannot be manufactured economically in the expected sales volume, or one that is substantially different from what the production units will be in regard to quality and reliability.

meritn. 优点 , 价值v. 有益于insofar adv.在 ... 的范围substantially adv. 充分地

Also, it is much better for design engineers to do a complete job of material analysis, selection, and specification at the development stage of design rather than to leave it to the production-design stage, where changes may be made by others, possibly less knowledgeable about all of the functional aspects of the product. At the production design stage, the primary concern relative to materials should be that they are specified fully, that they are compatible with, and can be processed economically by, existing equipment, and that they are readily available in the needed quantities.

As manufacturing progresses, it is inevitable that situations will arise that may require modifications of the materials being used. Experience may reveal that substitution of cheaper materials can be made. In most cases, however, changes are much more costly to make after manufacturing is in progress than before it starts. Good selection during the production-design phase will eliminate the necessity for most of this type of change.

inevitable adj. 不可避免的 , 必然的evitable adj. =avoidablemodification n. 更改 , 修改 , 修正reveal vt. 展现 , 显示 , 揭示 , 暴露substitution n.代替 , 取代作用 , 代入法 , 置换 Eliminate vt. 排除 , 消除v. 除去

The more common type of change that occurs after manufacturing starts is the result of the availability of new materials. These, of course, present possibilities for cost reduction and improved performance. However, new materials must be evaluated very carefully to make sure that all their characteristics are well established.

established adj.已制定的 , 确定的

One should always remember that it is indeed rare that as much is known about the properties and reliability of a new material as about those of an existing one. A large proportion of product failure and product-liability cases have resulted from new materials being substituted before their long-term properties were really known.

product liability insurance产品责任保险

Product liability actions have made it imperative that designers and companies employ the very best procedures in selecting materials. The five most common faults in material selection have been: (a) failure to know and use the latest and best information available about the materials utilized;

(b) failure to foresee, and take into account the reasonable uses for the product (where possible, the designer is further advised to foresee and account for misuse of the product, as there have been many product liability cases in recent years where the claimant, injured during misuse of the product, has sued the manufacturer and won);

claimant n.（根据权利）提出要求者 , 原告sue vt. 控告 , 向 ... 请求 , 请愿vi. 提出诉讼 , 提出请求

(c) the use of materials about which there was insufficient or uncertain data, particularly as to its long-term properties; (d) inadequate, and unverified, quality control procedures; and (e) material selection made by people who are completely unqualified to do so.

An examination of the faults above will lead one to conclude that there is no good reason why they should exist. Consideration of them provides guidance as to how they can be eliminated. While following the very best methods in material selection may not eliminate all product-liability claims, the use of proper procedures by designers and industries can greatly reduce their numbers.

claim n.( 根据权利提出 ) 要求 , 要求权 , 主张 , 要求而得到的东西vt.( 根据权利 ) 要求 , 认领 , 声称 , 主张 , 需要

From the previous discussion, it is apparent that those who select materials should have a broad, basic understanding of the nature and properties of materials and their processing.

apparent adj.显然的 , 外观上的

I Have NothingI Have Nothing whitney Houstonwhitney Houston

Share my life, take me for what I am Cause I'll never change all my colors for you Take my love, I'll never ask for too much Just all that you are and everything that you do

I don't really need to look very much further I don't want to have to go where you don't follow I won't hold it back again, this passion inside Can't run from myself There's nowhere to hide (Your love I'll remember forever)

Don't make me close one more door I don't wanna hurt anymore Stay in my arms if you dare Or must I imagine you there Don't walk away from me... I have nothing, nothing, nothing If I don't have you, you, you, you.

You see through, right to the heart of me You break down my walls with the strength of you

love I never knew love like I've known it with you

Will a memory survive, one I can hold on to

当别人在你旁边罗嗦个没完，你烦透了，说“ You are so boring “.( 你真烦！ ) 。“ Shut up !” （闭嘴！）自然没错，可人家受得了吗？不如来一句“ Oh, come on .Give me a break !” ( 帮帮忙，让我歇歇吧！ ) 这多地道、多幽默。

要想说人“气色好”。“ You look fine !”当然不错，可如果你说” You’re in the pink !” 就妙得多了，实际上，在英语口语中，表示颜色的词用起来非常形象生动。

遇到你不懂的问题时可别不懂装懂，“ I

know” 可能是中国人用得最多，而美国人最不能接受的一句话。当一美国教师向你解释某个问题时，你如果连说两遍“ I know” 可能是中国人用得最多，而美国人最不能接受的一句话。当一美国教师向你解释某个问题时，你如果连说两遍“ I know”, 我敢保证，他不会再跟你说什么了。用 “ I got it ” 就顺耳得多，要是不懂就说“ I’m not clear about it .” 不过如果你会说“ It’s past my understanding”或“ It’s

beyond me .” 你的教师定会惊讶不已的。

别人征求你的意见，问能否开窗户等，你要说“ You can do that .” 就有点土了，用一句“ Do you have the time? ” 实际上，问他人的姓名，地址都可以这么用：“ May I have you name?“ 要比” What’s your name ? ”礼貌得多，不过警察例外。　　别人问你不愿公开的问题，切勿用“ It’s

my secret ,Don’t ask such a personal question .”回答，一来显得你没有个性，二来也让对方尴尬。你可以说“ I would rather not say .” （还是别说了吧！）。

别人征求你的意见，问能否开窗户等，你要说“ You can do that .” 就有点土了，用一句“Do you have the time? ” 实际上，问他人的姓名，地址都可以这么用：“ May I have you name?“ 要比” What’s your name ? ”礼貌得多，不过警察例外。 有时候，你想说什么，可说是想不起来，你可以说“ Well …”“Let me see”“Just a moment ”或“ It’s on the tip of my tongue.” 等，想比之下，最后一个句型是最地道的。

在中国可不能随便说“我想你”，然而，当和西方人分手时说“ I will miss you .” 要比说“Good-bye”或“ See you soon” 有趣得多，不妨一试。　　有人开会迟到了，你若对他说 “ You are

late .” ，听起来象是废话，若说“ Did you get

lost ?” ，则更能让他歉然，可别说成“ Get lost!

”那可是让人滚蛋的意思。

“他精力充沛”美国人说：“ He is bouncy.”

而不说“ He is energetic ”,牢记一些日常对话中的活句式是你一把必备的钥匙。　　如：久仰，“ I get mind of you “.比” I

heard a lot about you.”轻松得多。 代问他人好当然能用” Please remember

me to your sister .” 或” Please give my best

wishes to your father ” 不过，若是很好的朋友，何不说，“ Please give my love to Jim ”。