Relationships Between Microstructure and Engineering Properties
- PDF / 649,410 Bytes
- 11 Pages / 420.48 x 639 pts Page_size
- 32 Downloads / 235 Views
RELATIONSHIPS BETWEEN MICROSTRUCTURE AND ENGINEERING PROPERTIES
P.L. PRATT Department of Materials, SW7 2BP, UK
Imperial College, Prince Consort Road,
London
ABSTRACT The calculation of such macroscopic engineering properties as elastic modulus and compressive strength for cement pastes and concrete depends upon Increasingly the establishment of a realistic model of the microstructure. complex models are considered, which appear capable of predicting the The same models elastic modulus in terms of a modified Rule of Mixtures. are able to account for the broad features of the compressive strength, because strength is always scaled by the elastic modulus of the material. The actual value of the compressive or the bend strength is determined by the mechanics of crack initiation and crack propagation in the particular test used. Crack initiation is controlled by the defects present in the material and crack propagation by the fracture toughness of the different Thus the strength depends phases and the porosity in the microstructure. upon microstructure in a number of different but interrelated ways, determined by the fracture toughness of the material.
INTRODUCTION Hornbogen [1] has defined microstructure as What is microstructure? the structural level between that of engineering structures and of individual phases in the material. Microstructure starts at a size just above one atomic spacing and may extend up to the size of the component. MicroIts structure comprises all discontinuities inside and between phases. elements are such non-equilibrium features of the structure as vacancies, dislocations, grain boundaries and phase interfaces and pores or particles. A quantitative description of microstructure requires information about the atomic structure of the defects, their density, shape and local distribution, and their orientation within the material, which may give rise to microstructural anisotropy. For multi-phase materials, information is needed about the volume fractions of phases, their distributions in space and the nature and amount of the interfaces between them. Hornbogen concluded: "These concepts of microstructure will have to be supplemented for cement and concrete. In addition to pores and fissures, structural gradients in the cement phase play an important role. A unified definition which includes cement and concrete will still require considerable efforts." While the development of microstructure with time during the hydration of cement is becoming better understood, the relationships between microfar from clear. In this structure and engineering properties are still paper an attempt is made to survey the methods used to calculate such properties as elastic stiffness, strength and toughness from observations of the microstructural features that are most involved in determining the engineering properties.
Mat. Res. Soc. Symp. Proc. Vol. 85. 1•987Materials Research Society
146
THE CALCULATION OF MACROSCOPIC PROPERTIES For coarse polyphase microstructures, macroscopic transport properties such
Data Loading...
