Ductile fracture. The propagation of a ductile crack involves substantial plastic flow and ductile fracture usually gives a characteristic rough fracture surface.Fracture occurs by a process known as microvoid coalescence. First, plastic strain causes small microvoids to form in the material, most often at sites of inclusions.he propagation of a ductile crack involves substantial plastic flow and ductile fracture usually gives a characteristic rough fracture surface.
An illustration of the space-time curvature caused by Earth. Space-time is a mathematical model that joins space and time into a single idea called a continuum. This four-dimensional continuum is known as Minkowski space. Combining these two ideas helped cosmology to understand how the universe works on the big level (e.g. galaxies) and small level (e.g. atoms).
Space-time. In his general theory of relativity, Einstein views gravity not as a force but as a curvature of the fabric of space in the presence of a massive object like a black hole (see Topic 2, Chapter 1 of this unit).According to Einstein, the fabric of space is a four-dimensional space representing the universe.his chapter looks at Einstein's special and general theories of relativity. It also explains related terms like 'time-space', 'gravity' and 'gravitation'.