通常所说的钢轨机械性能包括哪些？它们的含义是什么？
参考答案：
（1）钢轨的机械性能通常包括强度、塑性、硬度、韧性和疲劳。（2）它们的含意是：强度——钢轨在载荷作用下，抵抗变形和破坏的能力；塑性——金属材料在载荷作用下，产生显著的变形而不致破坏，并在载荷取消后，仍能保持变形后的形状能力；硬度——金属材料抵抗另一种更硬物体（材料）压入其表面的能力；韧性——是指金属材料抵抗冲击载荷作用而不致破坏的能力；疲劳——在交变载荷的作用下，材料发生断裂的现象。
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| A man's best friend may become his enemy. His children that he has 1 with loving care may show no thanks. Those who are 2 to us, those whom we trust with our happiness 3 turn against their faith. The money that a man has, he may 4 . It flies from him, perhaps when he needs it 5 . A man's reputation (名 誉) may be lost in a moment of ill-considered 6 . The people who would prefer to fall on their knees to do us honour when success is with us may be 7 to throw the stone malice (敌意) when failure settles upon our heads. The one absolutely (绝对地) 8 friend that man can have in this selfish world, the one that never deserts (遗弃) him is his 9 . A man's dog stands by him 10 he is rich or poor, healthy or sick. He will sleep on the cold ground, 11 the wintry winds blow and the snow drives hard, 12 he may be near his master's side. He will 13 the hand that has no food to offer. He guards the sleep of his poor master as if he 14 a prince. When all other friends desert him, the dog 15 . When reputation falls to pieces, he is as constant (不断的) in his love as the sun in its journey 16 the heavens. If the master becomes friendless and homeless, 17 the faithful dog asks for is to be with him. And when 18 takes his master in its embrace (拥抱) and his body 19 away in the cold ground, there by the graveside (墓边) will the dog be found, his head between his paws, his eyes sad but 20 in watchfullness, faithful and true even in death. | ||||
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