Measurement of residual stresses

Question 1

Which type of residual stress can we measure?

Answer 1

Type 1

Question 2

What are the three possible approaches for measuring residual stresses?

Answer 2

• Indirect measuring techniques based on mechanical methods
• Diffraction methods
• Other indirect methods are based on the evaluation of physical properties that can be correlated to residual stress state

Question 3

What is the principal of mechanical methods for measuring residual stresses?

Answer 3

Whenever a portion of a material is removed from a body containing a stress field, a new equilibrium is set to balance the removed layer. The pre-existing stress field can be calculated on the basis of the measured geometrical change

Question 4

How can diffraction methods measure residual stresses?

Answer 4

They can be used to evaluate the average lattice distortion from which the elastic strain can be evaluated

Question 5

What is the hole drilling strain gauge method?

Answer 5

A small hole is drilled in a part at the centre of a special strain gauge rosette. The locally relived surface strain around the hole is measured. The local residual stress (at hole centre) can then be calculated from these strains (formulaes or FEM)

Question 6

What is a resistance strain gauge?

Answer 6

A passive resistance transducer that converts the mechanical
elongation/compresison into a change of electrical resistance

Question 7

What are some of the indirect methods for measuring resiudal stresses?

Answer 7

• Using magnetic properties.
• Ultrasonic methods

Question 8

What are the advantages of diffraction with synchrotrons over standard X-rays?

Answer 8

• Increased penetration depth can provide high spatial resolution and threedimensional maps of the strain distribution to millimeter depths
• Very quick measurement

Question 9

What are the disadvantages of diffraction with synchrotrons compared to standard X-rays?

Answer 9

• Needs laboratory and specialist
• Very high costs