CHAPTER ONE
- INTRODUCTION
Material selection is a step in the process of designing any physical object. In the context of product design, the main goal of material selection is to minimize cost while meeting product performance goals. Systematic selection of the best material for a given application begins with properties and costs of candidate materials.
Understanding the material selection process is necessary for any form of application or design. The set of properties for a particular material is called the material attributes. Material selection involves seeking the best match between the design requirements and the material attributes. [“Material Selection”, 2014][1]
The selection of materials on a purely rational basis is a very difficult process, the process is not only often made difficult by insufficient property data but is typically one of decision making in the face of multiple constraints without a clear objective function.
The problem of material selection usually involves one or two difficulties such as;
- Selection of the material for a new product or design.
- Reevaluation of existing product or design to reduce cost, increase reliability, improves performance e t c.
Material selection like any other aspect of engineering design is a problem solving process whose steps can be defined by:
- Analysis of material/application requirement: This is to determine the conditions of service and environment that the product must be able to withstand.
- Possible materials: Possible materials are defined by the application requirements. For example; you cannot use clothes to build a bicycle. It also has to do with comparing the needed properties with a large material property data base to select a few materials that look promising for the application i.e. screening out of materials that fail the design constraints.
- Selection of Candidate Material: This is to analyze candidate materials in terms of trade-off of product performance, cost, processibility and availability to select the best material for the application.
- Development of Design Data: This is to determine experimentally the key material property of the selected material to obtain reliable statistical measures of the material performance under specific conditions to be encountered in service.
- Strengthening of Materials Using Material Selection Technique
If the materials available do not meet the requirements or do not have all the properties needed; the properties of the material can be changed using methods that are learned through Material Science Technique. Though, there are many manufacturing techniques used to strengthen and form materials; three common physical principles used for functional material strengthening are densification, composites and alloying.
Densification is the most common way to strengthen any material. Generally, this increases the tensile strength by reducing the porosity of the material. [“Material Selection”, 2014][1]
Composites are materials that are comprised of various parts. They can be natural e. g wood, rocks e t c and they can be manmade e.g.concrete. One of the major reasons for the prevalent use of composite materials in construction is the adaptability of the composite to many kinds of applications. The standard composite rule of mixtures is when standard matrix is soft and the reinforcing material is tensile strong. The selection of mixture proportions can result in the change of the mechanical properties of the material.
Alloying of metals is one of the oldest and most fundamental material processing techniques. An alloy is a solid solution that is composed of two or more elements. There is a solvent (majority composite) and a solute. The solute element can strengthen the overall solid solution by different element size, density and other material properties. [Mahmoud Farag, 2000][2]
The goal of design is to create products that perform their function effectively, safely and at an acceptable cost.
Given the application requirements, possible materials and physical principles (i.e. strengthening mechanism), we can select the best material. [George E. Dieter, 1997][3]
- Summary
The selection of materials for design involves:
- Deciding on the application requirements.
- Analysis of possible materials that can be used in the application.
- Deciding on the change in material properties that are needed and
- Choosing the material that best fulfills the requirements of the application given possible changes in the material properties.
- Material Properties
Material properties can be divided into:
- Physical properties i.e. Density, melting point, vapour pressure, viscosity, porosity, permeability.
- Chemical properties i.e. Corrosion, oxidation, thermal stability, stress corrosion.
- Electrical properties: Conductivity, coersive force, hysteresis and dielectric constant.
- Thermal Properties: Conductivity, specific heat, thermal expansion and emissivity.
- Mechanical properties: Hardness, elastic constants, yield strength, fracture toughness, wear resistance, ballistic performance.
- HISTORY
Development of civilization involves structural development (prehistory, including bridges, amphitheaters, dams, roads and canals. Building materials in present use have a long history and some of the structures built thousands of years ago are regarded as remarkable. [Mason, Robert B, 1995][4]
The history of building is marked by a number of trends. One is the increasing durability of the materials used with respect to these ages namely;
- Stone Age: This was a period roughly from 9000BC to 5000BC in which people use natural materials like stone, wood, bone, grasses e t c to construct buildings/structures.
- Bronze Age: The Bronze Age started around 3100BC. When people discovered how to make copper harder by alloying it with zinc, the trend changed and new tools and buildings were developed. The Egyptians began building stone temples with the post and lintel construction method.
- Iron Age: This is a cultural period from roughly 1200BC to 50BC. By adding carbon, iron becomes steel which was being produced after about 300BC. Steel can be hardened and tempered.
The chief building material was the mud-brick. By 3500BC, fired bricks came into use. Glazing of ceramics and stone paste ceramics were invented in the 8th and 9th century. Glass was introduced in the 15th century. [Mason, Robert B, 1995][4]
Now, more materials of higher quality than the ones previously mentioned are been fabricated by material scientist all over the world.
It is however surprising to know that with the alarming rate of fire outbreaks leading to loss of life and property and the advent of fire resistant materials, most Nigerians still consider beauty neglecting the overwhelming importance of the building- material property.
The discovery of cheap processes to make steel enabled the building of infrastructure of the industrial world. The accessibility or availability of suitable materials is responsible for the development of civilization.[Robert W. Chan, 2001][5]
- AIMS AND OBJECTIVES
The aim of this project is to consider the quality and cost of materials used in construction of buildings in Nigeria majorly in Benin.
The objectives are:
- To increase the use of quality building materials that is cost effective by construction engineers in Benin.
- To emphasize the importance of selecting and using materials that is safe or non-hazardous to the environment.
- JUSTIFICATION
The use of sub-standard materials account for about 10% of collapsed buildings in Nigeria [Oyewande, 2002] [6].One of the causes for the use of sub-standard materials is cost.
In this era where global warming and ozone layer depletion is of great concern as it could cause damage to the human habitat, the use of materials whose production process contribute negatively to the environment is a problem.
The analysis of building materials would help the designer choose the material that most suits the design requirement, at lower cost and at the same time environment friendly.
