Engineering materials: Brittle Fracture Mechanics and Considerations

One of most important concepts in Material engineering is fracture. Brittle fracture is key concern in Industrial Damage Mechanism and describe by sudden fracture in material under stress. As rule all materials of construction are at risk to damage and efforts have been made to prevent failures in tool caused by fracture mechanism. We will define and discuss brittle material preventions and Things affecting Brittle Fracture

What is Brittle Fracture?

Brittle fracture is described by low plastic deformation and small amounts of energy absorption at failure. There are two types of fracture found for most engineering materials, either ductile or brittle. This ductile fracture is set apart by large amount of plastic deformation before failure. This form of fracture involves large amount of energy absorption.

If cracks or sharp flaws are possible you need safety factor for brittle fracture is needed as well. Brittle fracture can occur due to static loads and involves little deformation, where as ductile fracture involves deformation.

Brittle fracture takes place when following four factors are present

  • Material has flaws inside
  • High-stress
  • Microstructure at risk
  • Transition temperature

Things affecting after Brittle Fracture

Most basic concern in design to avoid structural failure is that stress in component must not exceed strength of material, where strength is simply stress that cause deformation or fracture failure.  Fracture mechanics and brittle fracture are important in design of pressure vessels and large welded structures such as bridges and ships.

Flaws produce stress concentrations that cause premature failure. Stress may be left over while manufacturing and fabrication processes or applied externally by wind loadings. These cracks like flaws lead to terrible failure. Normally material in flaw is to develop in form of bigger cracks under high stresses.

Also, it is toughness of material which offers resistance to fracture. It means less toughness with material will provide less resistance and vice versa. Grain size in microstructure has significant effect on materials toughness and this is why microstructure will offer less resistance to fracture.

You can see failures in petrochemical and refining industries in tools which are operating below transition temperature because at this temperature, material toughness will decrease down and offers less resistance to brittle fracture. Read about Engineering Material – Normalizing

Railway tracks joined by thermite welding were focus to brittle fracture because thicker materials offer less resistance due to triaxial stresses on flaw if present. So thick many walled items must be given serious against fracture damage. Stresses may be applied for long periods of time. Stresses may be applied and removed or direction of stress is reversed.

Prevention of Brittle fracture

Enough Toughness

Brittle fracture can controlled by using right materials which offer sound resistance even at low temperature and maintain enough toughness to bear stresses. This materials will use with lower toughness at high stress are leads to failure. To prevent from this, you need to use tougher materials.

Use right material composition and microstructure

As per above that microstructure will more damage, so material with right chemical composition and microstructure must be used to avoid this damage. If tools is made-up by using welding, then this tools must be post repair heat and other thermal treatments must be done to prevent failure occur during service.

As we all aware that metal has brittle heat affected zone with grain size and proper post weld thermal treatment is required to reduce residual stresses and modify grain size. Check Engineering Materials – Desirable Bearing Materials Properties

Check Damage Mechanism

You must consider three factors to access chance of failure like stress level, size of flaw and toughness of material. Above three factors is best preventive method to control one or more above factors. If the toughness and size of flaw are unable to keep up stress level then material will leads to fracture. This is best controlled by monitoring damage mechanism, inspection of parts and operating conditions under high stress during tools service.

Factors to control Brittle Fracture

  • You can control brittle fracture by size, shape and depth of flaw
  • Material Chemical work
  • Toughness of material
  • Micro-structure
  • Concentration on stress
  • Operating temperature, pressure etc conditions
  • Transition temperature

Mechanical behavior of materials is study of deformation and fracture of materials. This material strength is compared with stresses expected for component in service to assure that design is adequate. You must check material parts from time to time there is any crack like flaw if present. Use streamline designs to prevent stress at sharp edges and joints.

On other hand, materials with sharp notches and cutting edges can raise stress and may cause cracking. Use tougher material which can remove lower temperature. You must give special attention to thicker materials because they are more prone to damage due to triaxial stresses on cracks. This crack spread under stress and may result in brittle fracture.