机械基本访谈问题和答案第4部分
Basic of Mechanical Engineering Interview, viva ,Oral Question and Answers Part 4
188金宝搏bet官方下载机械工程采访技术问题和答案，并解释了工作面试，竞争考试和入学考试。
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91. Which reactor produces more fissionable material than it consumes ?
育种反应堆。
92. Which reactor uses natural uranium as fuel ?
Gas cooled reacator.
93.哪个反应堆使用重水作为主持人？
反应堆。
94. Which reactor requires no moderator ?
育种反应堆。
95. Which reactor uses primary coolant as fluoride salts of lithium, beryllium, thorium and uranium ?
Molten salt breeder reactor.
96. Why an increase in area is required to produce an increase of velocity in case of supersonic flow ?
需要增加超音速流速度的面积增加，因为在超音速速度下的密度比速度的速度快于速度的速度快，并且要保持质量的连续性，则必须增加面积。
97.在什么情况下，发散喷嘴的压力会增加？
For subsonic flow at inlet section of a diffuser a lower velocity and higher pressure will exist at the exit section. For supersonic isentropic flow at the inlet section a higher velocity and lower pressure will exist at the exit but if a shock wave occurs in the diffuser then a higher pressure will exist at the exit.
98. Why water can’t be used as refrigerant for small refrigerating equipment ?
制冷剂应该使蒸气量较低，以使抽水工作较低。与给定质量相比，与R-相比，水蒸气量约为4000倍。
99.哪个参数在节流过程中保持恒定？
Enthalpy.
100. What is the difference between isentropic process and throttling process ?
In isentropic process, heat transfer takes place and in throttling process, enthalpy before and after the process is same.
101. What is the difference between isotropic and anisotropic materials ?
如果材料表现出相同的机械性能，无论负载方向如何，它都是各向同性的，例如均匀的铸造材料。缺乏这种特性的材料是各向异性的。
102.什么是骨材料？
它是一类特殊的各向异性材料，可以通过在三个垂直方向上给出其性质来描述，例如木头;复合材料。
103. What is view factor ?
视图因子取决于两个表面交换辐射的几何形状。
104. What properties need to be considered for applications calling for following requirements :
（i）刚性
（ii）在静态载荷下无塑性变形的强度
(iii) strength to withstand overload without fracture.
(iv) wear resistance
（v）可靠性和安全性。
（i）刚性 - 弹性模量和屈服强度
（ii）强度（对于静态载荷下没有塑性变形） - yield点
(iii) Strength (overload)—Toughness and impact resistance
（iv）耐药性 -
(v) Reliability and safety—Endurance limit and yield point.
105. Explain the effects of alloying chromium and nickel in stainless steel.
镍和铬的添加会增加拉伸强度，并增加对腐蚀的耐药性。
106. Mention two types of dislocations.
Dislocation refers to a break in the continuity of the lattice. In edge dislocation, one plane of atoms gets squeezed out. In screw dislocation the lattice atoms move form their regular ideal positions.
107. What are the principal constituents of brass?
Principal constituents of brass are copper and zinc.
108.什么是居里点？
居里点是不再用外部力磁化铁磁材料的温度。
109.当材料的特定强度在纤维尺寸时非常高，但是当它们处于条形的形式时，它们的特定强度较低？
晶体结构已排序，重复原子排列。纤维有责任维持这一点，因此具有很高的特异性强度。随着尺寸的增加，由于有几个
types of defects and dislocations and thus the specific strength gets lower.
110.铸铁中碳的百分比是多少？
2.5％。
111. Which element is added in steel to increase resistance to corrosion ?
Chromium.
112. Whether individual components in composite materials retain their characteristics or not?
yes.
113.当弹性伸长率的百分比时，弹性体是聚合物？
大于100％。
114.如果材料的伸长百分比超过200％，则将其归类为？
Rubber.
115. Why is it that the maximum value which the residual stress can reach is the elastic limit of the material ?
A stress in excess of elastic limit, with no external force to oppose it, will relieve itself by plastic deformation until it reaches the value of the yield stress.
116.为什么疲劳强度随着零件的大小增加超过10毫米的增加而降低？
材料条件的完美是在较低尺寸的情况下进行的，并且随着尺寸的增加，无法达到均匀的结构
of the material.
117. Distinguish between creep and fatigue.
Creep is low and progressive deformation of a material with time under a constant stress at high temperature applications. Fatigue is the reduced tendency of material to offer resistance to applied stress under repeated or fluctuating loading condition.
118. While normal carburising and nitriding surface treatments increase fatigue strength, excessive treatment may decreasethe fatigue strength. Why ?
Normal carburising/nitriding treatments increase volume due to phase transformation at Surface and introduce residual compressive surface stress and thus increase the fatigue strength. By excessive treatment the high compressive stresses are introduced but these are balanced by high in¬ternal tensile stresses of equal value and the subsurface fatigue cracks may develop in the regions of high tensile stress and lead to early fatigue failure.
119. List at least two factors that promote transition from ductile to brittle fracture.
负载方式和负载速率促进了从延性裂缝到脆性断裂的过渡。机器构件可能在静态负载下具有延展性故障，但在载荷波动时可能会以脆弱的方式失败。同样，材料可以证明在普通测试速度下的拉伸负荷下延性延展性故障，但是如果以高速施加载荷，则可能会脆弱。
120.（a）延性材料和（b）脆性材料使用哪些故障理论？
For ductile materials, theories of failure used are maximum shear stress theory, and maximum energy of distortion theory; while for brittle materials, theory of maximum principal stress, and maximum strain are used.
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