弹性和塑性

毫无疑问，您现在已经听说过弹性的概念。通俗地说，就是有些物质被拉伸后，又恢复了原来的形态。你已经尝试过弹弓。你不是吗？那是一种弹性物质。让我们深入了解弹性和可塑性的概念，以更多地了解物质的这两种特性。

弹性是物体在消除变形力后恢复其原始配置（形状和尺寸）的能力。当从塑料体中消除变形压力时，它们不会恢复到以前的结构。可塑性是指物体在去除变形力后失去弹性并产生永久性变形的质量。

什么是变形？

变形或扭曲的动作或过程称为变形。当您对物品施加力时，它会压缩或拉伸以对力作出反应。施加在单位面积上的力在力学中称为应力。应变是由于应力反应而发生的拉伸或压缩量。每种材料对压力的反应都不同。

该反应强烈依赖于物质的化学键类型。根据消除应力后发生的情况，变形可能是弹性的或塑性的，描述如下：

1. 弹性变形或弹性是当引起变化的外力和与之相关的应力被去除时消退的变形。
2. 塑性变形或塑性是由持续的力引起的固体形状的持续变形或变化。弹性变形和塑性变形的主要区别在于弹性变形是可逆的，而塑性变形是不可逆的。

弹性

When deformation forces are removed, a body’s property allows it to restore its previous size and shape, that property is known as Elasticity. Elasticity is a phenomenon that occurs at the molecular level.

弹性变形是当引起变形的外力和与之相关的张力消除时消散的变形。因此，弹性变形是可逆的和非永久性的。 “弹性”的化学概念最能描述弹性变形。弹性是物质在变形后恢复其原始状态的能力。

弹性变形主要由材料的化学键合决定。如果化学键可以通过变形而不断裂来承受高应力，则该物质可以发生弹性变形。

当对物质施加压力时，化学键应扩展或弯曲以满足这种需要。化学键的拉伸和弯曲应该只是暂时的。然而，原子在拉伸或弯曲过程中不会发生碰撞。然而，随着时间的推移，材料的弹性质量会下降，物质会变脆并失去延展性。

弹性物质：

诸如硫化橡胶之类的弹性体是弹性体的最大例子。硫化橡胶具有交联的聚合物结构。聚合物链之间存在硫桥。这些硫交联通过使其承受应力而提高了橡胶的柔韧性。

韧性材料的应力-应变曲线

延性材料的应力-应变曲线如上图所示。考虑金属铜。弹性区描述了弹性变形发生的程度。达到弹性极限后，材料会发生塑性变形，即永久变形。

可塑性

The ability of a body to lose its elasticity and develop a permanent deformation when a deforming force is removed is known as Plasticity.

塑性变形定义为由持续力引起的固体形状的持续变形或变化。当对材料施加大量张力时，就会发生这种情况。塑性变形是永久的和不可逆的。可塑性是永久成型或模制的能力。

塑性变形是由于构成材料的原子之间的一些化学键断裂而发生的。在塑性变形过程中，原子可能会相互滑过。由于原子位错，当移除施加的张力时，材料保持静止。

延性材料的弹性极限是塑性变形的起点。固体的弹性极限是在不永久改变大小或形状的情况下可以拉伸的最大量。如果张力超过弹性极限，物质将发生塑性变形。

塑料物质：

金属、聚合物、岩石和其他材料表现出可塑性。当变形超过弹性极限时，塑性变形发生在金属（例如铜）等延展性材料中。然而，在岩石等脆性材料中，在塑性变形开始之前可能没有检测到弹性变形。塑性变形对于利用热处理或压力处理以及成型制造新产品至关重要。

材料行为的差异基于其弹性和塑性性质。也就是说，材料根据其弹性对一定的力作出反应。这是对塑料体和弹性体施加力的区别。

弹性和塑性的区别

	Elasticity	Plasticity
1.	Elasticity is the property of a solid material that allows it to restore its shape after an external load is removed.	Plasticity is the property of a solid substance that allows it to keep its deformed shape even when the external load is removed.
2.	The amount of external force necessary to bend a solid elastically is quite tiny.	The amount of external force necessary to bend a solid elastically is high.
3.	Hooke’s Law of elasticity is applicable within this elastic region.	Hooke’s Law of elasticity is not applicable within this plastic region.
4.	The stress-strain curve is linear in the elastic region mostly.	The stress-strain curve is non-linear in the plastic region
5.	Many properties of the solid material remain the same for elastic deformation.	Many properties of the solid material change considerably for plastic deformation.
6.	Elastic deformation occurs first than plastic deformation.	Plastic deformation occurs only after the body undergoes elastic deformation.
7.	Here deformation is reversible.	Here deformation is irreversible.
8.	Elasticity is used in – Machine tool structures, Bridges, other civil frames, many household structures that should retain their shape etc.	Plasticity is used in various forming operations such as rolling, forging, extrusion, etc, sheet metal working, Rivet joining etc.

弹性的应用

• 我们知道起重机是用来提升和移动重物的。起重机配备有粗金属绳索。起重机在任何情况下所承受的最大载荷不应超过绳索材料的弹性极限。通过了解该弹性极限和材料每单位长度的延伸，可以评估线材的横截面积。由此，可以计算出线的半径。
• 弹性用于估计地球上一座山的最大高度。
• 弹性用于桥梁的设计。在设计一座桥梁时，我们必须考虑一些因素，如交通负荷、桥梁的重量、风力。这座桥的设计既不会过度弯曲也不会断裂。

示例问题

问题 1：定义弹性疲劳及其影响。

解决方案：

Elastic fatigue is a condition in which the elasticity of a material is temporarily lost as a result of continual strain.

The effect of elastic fatigue are:

• Within the elastic limit, a wire can be broken.
• Without the use of equipment, a wire can be sliced into pieces.
• After a long period of service, railway tracks and bridges are deemed hazardous.
• After a long period of usage, spring balances give incorrect readings.

问题 2：解释 Elastic 后效。

解决方案：

Elastic after effect refers to the time it takes for a material to restore its previous length after a deforming force is removed.

• Elastic after effect for a perfectly elastic body is zero.
• Elastic after effect for a perfectly inelastic body is infinite.

问题 3：当对物体施加力时会发生什么？

解决方案：

If we apply force on an elastic body like rubber then it stretches up to the elastic limit. If we apply the same force continuously then it may break. And whenever we stop applying force then it regains its original shape. But coming to the plastic body like an aluminum rod, when we apply force on that plastic body then it may somewhat change its shape but after stopping the force it won’t regain its original shape.

问题4：什么是塑料？另外，提一下它的特点。

解决方案：

A plastic substance is one that does not exhibit elastic behavior. Putty, chewing gum, lead solder, and wax are some of the examples.

Some of the main characteristic properties of a plastic substance are:

1. More elastic is a body that is more difficult to strain.
2. Rubber is less elastic than steel.
3. Steel, not copper, is used to make springs because steel is more elastic than copper.
4. Elasticity is increased through hammering, rolling, and adding impurities.
5. The elasticity of the material is reduced by annealing and increasing the temperature.
6. Some material’s elasticity does not change as a function of temperature. One example of this is Invar Steel.

问题 5：什么是弹性体？也举出它的例子。

解决方案：

The term “elastic body” refers to a body that exhibits elasticity. Steel and rubber are the two examples.

Some of the approximate examples of a perfectly elastic body are Quartz and phosphor bronze.

问题 6：一个重物连接在一根细线上，并在垂直圆周上旋转。电线最有可能在哪一点断裂？

解决方案：

When heavy mass is attached to a thin wire and is whirled in a vertical circle, the wire will break at lowest point of a vertical wire because tension is more at that point.