tailieunhanh - INTRODUCTION TO COMPOSITE MATERIALS

Module này giới thiệu các khái niệm cơ bản của độ cứng và sức mạnh cơ bản cơ chế gia cố vật liệu sợi tổng hợp tiên tiến. Khía cạnh này của công nghệ vật liệu composite là đôi khi thuật ngữ "micromechanics," bởi vì nó đề với các mối quan hệ giữa các đặc tính kỹ thuật vĩ mô và phân phối các vi thành phần của vật liệu, cụ thể là các phần nhỏ khối lượng chất xơ. | INTRODUCTION TO COMPOSITE MATERIALS David Roylance Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 March 24 2000 Introduction This module introduces basic concepts of stiffness and strength underlying the mechanics of fiber-reinforced advanced composite materials. This aspect of composite materials technology is sometimes terms micromechanics because it deals with the relations between macroscopic engineering properties and the microscopic distribution of the material s constituents namely the volume fraction of fiber. This module will deal primarily with unidirectionally-reinforced continuous-fiber composites and with properties measured along and transverse to the fiber direction. Materials The term composite could mean almost anything if taken at face value since all materials are composed of dissimilar subunits if examined at close enough detail. But in modern materials engineering the term usually refers to a matrix material that is reinforced with fibers. For instance the term FRP for Fiber Reinforced Plastic usually indicates a thermosetting polyester matrix containing glass fibers and this particular composite has the lion s share of today s commercial market. Figure 1 shows a laminate fabricated by crossplying unidirectionally-reinforced layers in a 0o-90 stacking sequence. Many composites used today are at the leading edge of materials technology with performance and costs appropriate to ultrademanding applications such as spacecraft. But heterogeneous materials combining the best aspects of dissimilar constituents have been used by nature for millions of years. Ancient society imitating nature used this approach as well the Book of Exodus speaks of using straw to reinforce mud in brickmaking without which the bricks would have almost no strength. As seen in Table 11 the fibers used in modern composites have strengths and stiffnesses far above those of traditional bulk materials. The high strengths