機械工程英語課文翻譯(編輯修改稿)

　

【文章內容簡介】 通常可采用加強復合結構來改善。Important Characteristics of Polymers Size. Single polymer molecules typically have molecular weights between 10,000 and 1,000,000g/mol—that can be more than 2,000 repeating units depending on the polymer structure! 聚合材料的重要特性 尺寸：單個聚合物分子一般分子量為10,000到1,000,000g/mol之間，具體取決于聚合物的結構—這可以比2,000個重復單元還多。The mechanical properties of a polymer are significantly affected by the molecular weight, with better engineering properties at higher molecular weights.聚合物的分子量極大地影響其機械性能，分子量越大，工程性能也越好。 Thermal transitions. The softening point (glass transition temperature) and the melting point of a polymer will determine which it will be suitable for applications. These temperatures usually determine the upper limit for which a polymer can be used. 熱轉換性：聚合物的軟化點(玻璃狀轉化溫度)和熔化點決定了它是否適合應用。這些溫度通常決定聚合物能否使用的上限。For example, many industrially important polymers have glass transition temperatures near the boiling point of water (100℃, 212℉), and they are most useful for room temperature applications. Some specially engineered polymers can withstand temperatures as high as 300℃(572℉).例如，許多工業上的重要聚合物其玻璃狀轉化溫度接近水的沸點(100℃, 212℉)，它們被廣泛用于室溫下。而某些特別制造的聚合物能經受住高達300℃(572℉)的溫度。 Crystallinity. Polymers can be crystalline or amorphous, but they usually have a bination of crystalline and amorphous structures (semicrystalline). 結晶度：聚合物可以是晶體狀的或非結晶質的，但它們通常是晶體狀和非結晶質結構的結合物(半晶體)。 Interchain interactions. The polymer chains can be free to slide past one another (thermoplastic) or they can be connected to each other with crosslinks (thermoset or elastomer). Thermoplastics can be reformed and recycled, while thermosets and elastomers are not reworkable. 原子鏈間的相互作用：聚合物的原子鏈可以自由地彼此滑動(熱可塑性)或通過交鍵互相連接(熱固性或彈性)。熱可塑性材料可以重新形成和循環使用，而熱固性與彈性材料則是不能再使用的。 Intrachain structure. The chemical structure of the chains also has a tremendous effect on the properties. Depending on the structure the polymer may be hydrophilic or hydrophobic (likes or hates water), stiff or flexible, crystalline or amorphous, reactive or unreactive. 鏈內結構：原子鏈的化學結構對性能也有很大影響。根據各自的結構不同，聚合物可以是親水的或憎水的(喜歡或討厭水)、硬的或軟的、晶體狀的或非結晶質的、易起反應的或不易起反應的。第二單元 The understanding of heat treatment is embraced by the broader study of metallurgy. Metallurgy is the physics, chemistry, and engineering related to metals from ore extraction to the final product. 對熱處理的理解包含于對冶金學較廣泛的研究。冶金學是物理學、化學和涉及金屬從礦石提煉到最后產物的工程學。Heat treatment is the operation of heating and cooling a metal in its solid state to change its physical properties. According to the procedure used, steel can be hardened to resist cutting action and abrasion, or it can be softened to permit machining. 熱處理是將金屬在固態加熱和冷卻以改變其物理性能的操作。按所采用的步驟，鋼可以通過硬化來抵抗切削和磨損，也可以通過軟化來允許機加工。With the proper heat treatment internal stresses may be removed, grain size reduced, toughness increased, or a hard surface produced on a ductile interior. The analysis of the steel must be known because small percentages of certain elements, notably carbon, greatly affect the physical properties.使用合適的熱處理可以去除內應力、細化晶粒、增加韌性或在柔軟材料上覆蓋堅硬的表面。因為某些元素(尤其是碳)的微小百分比極大地影響物理性能，所以必須知道對鋼的分析。 Alloy steel owe their properties to the presence of one or more elements other than carbon, namely nickel, chromium, manganese, molybdenum, tungsten, silicon, vanadium, and copper. Because of their improved physical properties they are used mercially in many ways not possible with carbon steels. 合金鋼的性質取決于其所含有的除碳以外的一種或多種元素，如鎳、鉻、錳、鉬、鎢、硅、釩和銅。由于合金鋼改善的物理性能，它們被大量使用在許多碳鋼不適用的地方。 The following discussion applies principally to the heat treatment of ordinary mercial steels known as plain carbon steels. With this process the rate of cooling is the controlling factor, rapid cooling from above the critical range results in hard structure, whereas very slow cooling produces the opposite effect. 下列討論主要針對被稱為普通碳鋼的工業用鋼而言。熱處理時冷卻速率是控制要素，從高于臨界溫度快速冷卻導致堅硬的組織結構，而緩慢冷卻則產生相反效果。? A Simplified Ironcarbon Diagram簡化鐵碳狀態圖 If we focus only on the materials normally known as steels, a simplified diagram is often used. 如果只把注意力集中于一般所說的鋼上，經常要用到簡化鐵碳狀態圖。Those portions of the ironcarbon diagram near the delta region and those above 2% carbon content are of little importance to the engineer and are deleted. A simplified diagram, such as the one in , focuses on the eutectoid region and is quite useful in understanding the properties and processing of steel. 鐵碳狀態圖中靠近三角區和含碳量高于2%的那些部分對工程師而言不重要，因此將它們刪除。，這對理解鋼的性能和處理是十分有用的。 The key transition described in this diagram is the deposition of singlephase austenite(γ) to the twophase ferrite plus carbide structure as temperature drops. 在此圖中描述的關鍵轉變是單相奧氏體(γ) 隨著溫度下降分解成兩相鐵素體加滲碳體組織結構。Control of this reaction, which arises due to the drastically different carbon solubility of austenite and ferrite, enables a wide range of properties to be achieved through heat treatment.控制這一由于奧氏體和鐵素體的碳溶解性完全不同而產生的反應，使得通過熱處理能獲得很大范圍的特性。 To begin to understand these processes, consider a steel of the eutectoid position, % carbon, being slow cooled along line xx’ in . At the upper temperatures, only austenite is present, the % carbon being dissolved in solid solution with the iron. When the steel cools to 727℃(1341℉), several changes occur simultaneously. 為了理解這些過程，%的共析鋼，’線慢慢冷卻。在較高溫度時，只存在奧氏體，%的碳溶解在鐵里形成固溶體。當鋼冷卻到727℃ (1341℉)時，將同時發生若干變化。 The iron wants to change from the FCC austenite structure to the BCC ferrite structure, but the ferrite can only contain % carbon in solid solution. 鐵需要從面心立方體奧氏體結構轉變為體心立方體鐵素體結構，%的碳。The rejected carbon forms the carbonrich cementite intermetallic with position Fe3C. In essence, the net reaction at the eutectoid is austenite %C→ferrite %C+cementite %C.被析出的碳與金屬化合物Fe3C形成富碳的滲碳體。本質上，%的碳→%的碳+%的碳。 Since this chemical separation of the carbon ponent occurs entirely in the solid state, the resulting structure is a fine mechanical mixtu