The SI unit of stress and pressure is the N/m2 or the Pascal (Pa), but from a materials point of view it is very small. The levels of stress large enough to distort or deform materials are measured in megaPascals (MPa). The table list the conversion factors relating MPa to measures of stress used in […]
Category: Materials and the Environment: Eco-Informed Material Choice
Appendix – Useful numbers and conversions
CONTENTS A1 Introduction A.1 Introduction Quantitative analysis needs numbers. Many of those needed to understand and quantify eco-aspects of material production and use are presented in the Chapters of the text. ■ Table 2.1: approximate efficiency factors for energy conversion and the associated CO2 emission per useful MJ. ■ Table 6.5: the energy content of […]
Plywood
The material. Plywood is laminated wood, the layers glued together such that the grain in successive layers are at right angles, giving stiffness and strength in both directions. The number of layers varies but is always odd (3, 5, 7 …) to give symmetry about the core ply; if it is asymmetric it warps when […]
Paper and cardboard
The material. Papyrus, the forerunner of paper, was made from the flower stem of the reed, native to Egypt; it has been known and used for over 5000 years. Paper, by contrast, is a Chinese invention (105 AD). It is made from pulped cellulose fibers derived from wood, cotton, or flax. There are many types […]
Flexible polymer foam
The material. Polymer foams are made by the controlled expansion and solidification of a liquid or melt through a blowing agent; physical, chemical, or mechanical blowing agents are possible. The resulting cellular material has a lower density, stiffness, and strength than the parent material, by an amount that depends on its relative density—the volume fraction […]
Rigid polymer foam
The material. Polymer foams are made by the controlled expansion and solidification of a liquid or melted through a blowing agent; physical, chemical, or mechanical blowing agents are possible. The resulting cellular material has a lower density, stiffness, and strength than the parent material, by an amount that depends on its relative density—the volume fraction […]
Sheet molding compound (SMC)
The material. Layup and filament winding methods of shaping composites are far too slow and labor intensive to compete with steel pressings for car body panels and other enclosures. Sheet molding compounds (SMCs) overcome this by allowing molding in a single operation between heated dies. To make SMC, polyester resin containing thickening agents and cheap […]
GFRP (Isotropic)
The material. Composites are one of the great material developments of the 20th century. Those with the highest stiffness and strength are made of continuous fibers (glass, carbon, or Kevlar, an aramid) embedded in a thermosetting resin (polyester or epoxy). The fibers carry the mechanical loads, whereas the matrix material transmits loads to the fibers […]
CFRP (Isotropic)
The material. Carbon fiber reinforced composites (CFRPs) offer greater stiffness and strength than any other type, but they are considerably more expensive than GFRP (see record). Continuous fibers in a polyester or epoxy matrix give the highest performance. The fibers carry the mechanical loads, whereas the matrix material transmits loads to the fibers and provides […]
Hybrids: composites, foams, and natural materials
Composites are one of the great material developments of the 20th century. Those with the highest stiffness and strength are made with continuous fibers of glass, carbon, or Kevlar (an aramid) embedded in a thermosetting resin (polyester or epoxy). The fibers carry the mechanical loads, whereas the matrix material transmits loads to the fibers, provides […]