1.4 COMPETITION AMONG MATERIALS
1.4 材料之间的竞争

Materials compete with each other for existing and new markets. Over a period of timemany factors arise that make it possible for one material to replace another for certainapplications. Certainly cost is a factor. If a breakthrough is made in' the processing ofa certain type of material SO that its cost is decreased substantially, this material mayreplace another for some applications. Another factor that causes material replacementchanges is the development of a new material with special properties for some appli-cations. As a result, over a period of time, the usage 'of different materials changes.
材料在现有市场和新市场之间相互竞争。在一段时间内，出现了许多因素，使一种材料在某些应用中取代另一种材料成为可能。当然，成本是一个因素。如果在某种类型的材料的加工方面取得突破，从而大大降低其成本，那么这种材料可能会在某些应用中取代另一种材料。导致材料更换变化的另一个因素是针对某些应用开发具有特殊性能的新材料。因此，在一段时间内，“不同材料的使用”发生了变化。

Figure 1.14 shows graphically how the production of six materials in the UnitedStates on a weight basis varied over the past years. Aluminum and polymers showan outstanding increase in production since 1930. On a volume basis the productionincreases for aluminum and polymers are even more accentuated since these arelight materials.
图 1.14 以图形方式显示了过去几年美国六种材料的产量按重量计算的变化情况。自 1930 年以来，铝和聚合物的产量显着增长。从产量上看，铝和聚合物的产量增长更加明显，因为这些是轻质材料。

The competition among materials is evident in the composition of the U.S. auto.In 1978, the average U.S. auto weighed 4000 lb (1800 kg) and consisted of about60 percent cast iron and steel, 10 to 20 percent plastics, and 3 to 5 percent alu-minum, The 1985 U.S. auto by comparison weighed an average of 3100 lb (1400 kg)and consisted of 50 to 60 percent cast iron and steel, 10 to 20 percent plastics, ana5 to 10 percent aluminum. Thus, in the period 1978- -1985 the percentageof steeldeclined, that of polymers increased, and that of aluminum remainedabout thesame. In 1997 the domestic U.S. auto weighed an average of 3248 lb (1476 Kg),and plastics comprised about 7.4 percent of it (Fig. 1.15). The trend in the usageof materials appears to be more aluminum and steel in autos and less cast 1ron.Theamount of plastics (by percentage) in autos appears to be about the same (F1g·1.16).For some applications only certain materials can meet the engineeringrequire-ments for a design, and these materials may be relatively expensive.For example,the modern jet engine (Fig. 1.5) requires high-temperature nickel-base superaluadto function. These materials are expensive, and no cheap substitute hasbeenfound to replace them. Thus, although cost is an important factor in engineering design,the materials used must also meet performance specifications. Replacement of onematerial by another will continue in the future since new materials are being dis-covered and new processes are being developed.
材料之间的竞争在美国汽车的成分中显而易见。1978 年，美国汽车的平均重量为 4000 磅（1800 公斤），由约 60% 的铸铁和钢、10% 至 20% 的塑料和 3% 至 5% 的铝组成，相比之下，1985 年的美国汽车平均重 3100 磅（1400 公斤），由 50% 至 60% 的铸铁和钢组成， 10% 到 20% 的塑料，ANA5% 到 10% 的铝。因此，在 1978--1985 年期间，钢的百分比下降，聚合物的百分比增加，而铝的百分比大致保持不变。1997 年，美国国内汽车的平均重量为 3248 磅（1476 公斤），塑料约占其中的 7.4%（图 1.15）。材料使用的趋势似乎是汽车中更多的铝和钢，而更少的铸造 1ron。汽车中的塑料数量（按百分比计算）似乎大致相同 （F1g·1.16）。对于某些应用，只有某些材料可以满足设计的工程要求，而这些材料可能相对昂贵。例如，现代喷气发动机（图 1.5）需要高温镍基 superaluadto 功能。这些材料很昂贵，而且没有找到便宜的替代品来替代它们。因此，尽管成本是工程设计中的一个重要因素，但所使用的材料也必须满足性能规格。由于新材料正在被发现，新工艺正在开发中，因此未来将继续用另一种材料替代一种材料。

1.5.1 Smart Materials
1.5.1 智能材料

Some smart materials have been around for years but are finding more applications.They have the ability to sense external environmental stimuli (temperature, stress,light, humidity, and electric and magnetic fields) and respond to them by changingtheir properties (mechanical, electrical, or appearance), structure, or functions. Thesematerials are generically called smart materials. Smart materials or systems thatuse smart materials consist of sensors and actuators. The sensory component detectsa change in the environment, and the actuator component performs a specific func-tion or a response. For instance, some smart materials change or produce color whenexposed to changes in temperature, light intensity, or an electric current.
一些智能材料已经存在多年，但正在寻求更多应用。它们能够感知外部环境刺激（温度、压力、光线、湿度以及电场和磁场），并通过改变其特性（机械、电气或外观）、结构或功能来响应它们。这些材料通常称为智能材料。智能材料或使用智能材料的系统由传感器和执行器组成。传感组件检测环境的变化，而致动器组件执行特定的功能或响应。例如，一些智能材料在暴露于温度、光强度或电流变化时会发生变化或产生颜色。

Some of the more technologically important smart materials that can functionas actuators are shape-memory alloys and piezoelectric ceramics. Shape-memoryalloys are metal alloys that, once strained, revert back to their original shape uponan increase in temperature above a critical transformation temperature. The changein shape back to the original is due to a change in the crystal structure above thetransformation temperature. One biomedical. application of a shape-memory alloys is as a stent for supporting weakened artery walls or for expanding narrowed arteries(Fig. 1.17). The deformed- stent is first delivered in the appropriate position in theartery using a probe Fig. 1:17a. The stent expands to its original shape and size afterincreasing its temperature to body temperature .Fig. 1.17b. For comparison, the con-ventional method of expanding or supporting an artery is through the use of a stain-less steel tube that is expanded using a ballon. Examples of shape-memory alloysare nickel -titanium 'and copper-zinc-aluminum alloys.
一些技术上更重要的可以用作致动器的智能材料是形状记忆合金和压电陶瓷。形状记忆合金是金属合金，一旦应变，温度升高超过临界相变温度，就会恢复到原来的形状。形状变回原来的是由于晶体结构的变化高于相变温度。一个生物医学。形状记忆合金的应用是作为支撑薄弱动脉壁或扩张狭窄动脉的支架（图 1.17）。首先使用探针将变形的支架输送到心脏的适当位置图 1：17a。支架在将其温度升高到体温后膨胀到原来的形状和大小。图 1.17b.相比之下，扩张或支撑动脉的常规方法是使用使用气球扩张的无不锈钢管。形状记忆合金的例子是镍-钛 ' 和铜-锌-铝合金。

Actuators may also be made of piezoelectric materials. The materials producean electric field when exposed to a mechanical force. Conversely, a change in anexternal electric field will produce a mechanical response in the same material. Suchmaterials may be used to sense and reduce undesirable vibrations of a componentthrough their actuator response. Once a vibration is detected, a current is appliedto produce a mechanical response that counters the effect of the vibration.
促动器也可以由压电材料制成。这些材料在受到机械力时会产生电场。相反，外部电场的变化将在同一材料中产生机械响应。此类材料可用于通过其执行器响应来感应和减少组件的不良振动。一旦检测到振动，就会施加电流以产生机械响应，以抵消振动的影响。

Now let us consider the design and development of systems at micrometer sizescale that use smart materials and devices to sense, communicate, and actuate: suchis the world of microelectromechanical systems(MEMs), Originally, MEMs weredevices that integrated technology, elcctronic materials, and smart materials on asemiconductor chip to' produce what were commonly known as a micromachines.The original MEMs device had the microscopic mechanical elements fabricated onsilicon chips using integrated circuits technology; MEMs were used as sensors oractuators. But today the term "MEMs" is extended to any miniaturized device. Theapplications of MEMs are also numerous, including but not limited to micropumps,locking systems, motors, mirrors, and sensors. For instance, MEMs are used in auto-mobile airbags to sense both the deceleration and the size of the person sitting inthe car and to deploy the airbag at a proper speed,
现在让我们考虑一下微米级系统的设计和开发，这些系统使用智能材料和设备来传感、通信和驱动：这就是微机电系统 （MEM） 的世界，最初，MEM 是将技术、电子材料和智能材料集成在非半导体芯片上的设备，以生产通常所说的微型机器。最初的 MEMS 设备采用集成电路技术在硅芯片上制造微观机械元件;MEM 用作传感器或执行器。但今天，“MEMs”一词已扩展到任何小型化设备。MEMS 的应用也很多，包括但不限于微泵、锁定系统、电机、镜子和传感器。例如，MEMS 用于汽车安全气囊中，以感应车内人员的减速和大小，并以适当的速度展开安全气囊。