The current tendency is to develop（采用） lighter materials, aluminum, for example, weighs much less than steel but has many of the same properties. Aluminum beams have already been used for bridge construction and for the framework of a few buildings.
            目前的趋势是采用较轻的材料。例如，铝的重量比钢轻得多，但具有很多相同的性能。铝材梁已经用于桥梁建筑和一些建筑的框架。
            Lightweight concretes, another example, are now rapidly developing（发展） throughout the world. They are used for their thermal insulation(绝热性). The three types are illustrated below（举例说明如下）: (a) Concretes made with lightweight aggregates; (b) Aerated concretes (US gas concretes) foamed（起泡） by whisking（搅拌）or by some chemical process during casting; (c) No-fines concretes.
            另一个例子是轻质混凝土，如今已在全世界快速地发展，因它们的绝热性而被采用，其三种类型举例说明如下：(a)轻质骨料制成的混凝土；(b)通过浇筑时搅拌或一些化学方法起泡而成的加气混凝土（US加气混凝土）；(c)无细骨料混凝土。
             All three types are used for their insulating properties（绝热性）, mainly in housing, where they give high（非常） comfort in cold climates and a low cost of cooling（降温成本）in hot climates. In housing, the relative weakness of lightweight concrete walls is unimportant, but it matters（有重大关系） in roof slabs, floor slabs and beams.
            这三种类型的混凝土都是由于它们的绝热性而被使用，主要用于房屋，使其在寒冷的气候中非常舒服，在炎热的气候中降温的成本不高。在房屋中，墙采用较薄弱的轻质混凝土不重要，但是屋面板、楼面板和梁（采用轻质混凝土）则有重大关系。
             In some locations, some lightweight aggregates cost little more than（几乎等于） the best dense（致密） aggregates and a large number of （大量） floor slabs have therefore been built of lightweight aggregate concrete purely for its weight saving, with no thought of（没考虑） its insulation value.
            在某些地区，一些轻质骨料的费用几乎等于最致密的骨料，因此大量的楼面板采用轻骨料混凝土制作纯粹是节约重量，而没考虑它的绝热价值。
            The lightweight aggregate reduces the floor dead load（恒载） by about 20 per cent resulting in（导致）considerable savings in the floor（楼盖结构） steel in every floor and the roof, as well as in the column steel and (less) in the foundations. One London contractor（承包商）prefers to use lightweight aggregate because it gives him the same weight reduction in the floor slab as the use of hollow tiles, with simpler organization and therefore higher speed and profit. The insulation value of the lightweight aggregate is only important in the roof insulation, which is greatly improved（改进）.
        轻质骨料使楼面的恒载减少了约20%，因而大量的节约了每层楼面以及屋面的楼盖结构中的钢材和柱子与基础中（较少）的钢材使用量。一位伦敦的承包商宁愿使用轻质骨料，因为这使楼面板上减少的重量与用空心砖相同，且组织更简单，因而速度和利润更高。轻质骨料的绝热价值只在屋面绝热时显得重要，它已被大大地改进了。


UNIT 4
             Mechanics of Materials deals with（研究）the response of various bodies, usually called members（构件）, to applied forces（施加力）. In Mechanics of Engineering Materials the members have shapes that either exist in actual structures or are being considered for their suitability（根据其需要）as parts of proposed（拟建的）engineering structures. The materials in the members have properties that are characteristic of commonly used（常用的）engineering materials such as steel, aluminum, concrete, and wood.
            材料力学用以研究不同物体（通常称为构件）对施加力的响应。在工程材料力学中，构件的形状可以是实际结构中存在的，也可以根据其需要而进行考虑（设计），作为拟建工程结构的部件。构件中材料的性能即是常用的工程材料如钢材、铝材、混凝土和木材的特性。
            As you can see already from the variety of materials, forces, and shapes mentioned, Mechanics of Engineering Materials is of interest to（对..有价值）all fields of engineering. The engineer uses the principles of Mechanics of Materials to determine if the material properties and the dimensions of a member are adequate to（足以）ensure that it can carry its loads safely and without excessive distortion. In general（通常）, then, we are interested in both the safe load that a member can carry and the associated（相关的）deformation. Engineering design would be a simple process if the designer could take into consideration（考虑）the loads and the mechanical properties of the materials, manipulate（利用）an equation, and arrive at（得到）suitable dimensions.