Before you read this, I suggest you read posts 20.9 and 20.10. In post 20.10 I described toughness as the energy absorbed by a unit volume of material before it fractures. It is often simpler to understand the process of fracture (when something breaks, post 20.10) in terms of energy rather than the stress (or… Continue reading 20.13 Fracture

Like most people, I hadn’t thought much about this topic until the last few weeks. But covid-19 means that every day we see numbers related to the spread of a pandemic. An epidemic has been defined as the “widespread occurrence of infection in a community in a given time”. A pandemic has been defined as… Continue reading 20.12 What happens in a pandemic?

Before you read this, I suggest you read posts 20.2, 20.6 and 20.8. In post 20.5, we saw that a material that maintained a constant volume, when it is stretched, has a Poisson’s ratio of 0.5. The Poisson’s ratio of rubber is approximately equal of 0.5, so any volume change, when it is stretched, are… Continue reading 20.11 Elasticity of rubber

Before you read this, I suggest you read post 20.9. In everyday English “toughness” and “strength” are used to mean the same thing. But in science such words are often given very specific meanings to avoid confusion (post 17.14). Then “toughness” and “strength” have precise and different meanings. It is sometimes helpful to have an… Continue reading 20.10 Toughness

Before you read this, I suggest you read post 20.2. Concrete is stiff – you can’t see it change dimensions or shape (it doesn’t deform very much) when subjected to a force. Steel is stiff too – you don’t usually see appreciable deformations in most of its applications. We think that concrete and steel are… Continue reading 20.9 Stiffness and strength