Tensile test

This article provides answers to the following questions, among others:

  • What kind of tensile specimens are usually used?
  • Why must the tensile specimens not be deformed too quickly?
  • Which quantities are measured during the tensile test?
  • Why does the yield strength play a central role in mechanical engineering?
  • Which material property is described by the elastic modulus?
  • What is the “yield strength effect”?
  • What is “yield point elongation” and what is the role of “Cottrell atmosphere”?
  • What are Lüder bands (stretcher strain marks)?
  • How does the “Portevin-Le Chatelier effect” (dynamic strain aging) occur?
  • Why does “uniform elongation” play an important role in forming technology?
  • Why does the tension curve  drop during necking?
  • Why do shorter tensile specimens show higher elongation at break than longer ones?
  • Which statement can be made on the basis of the area under the stress-strain curve?
  • What is the difference between the strength values and the deformation values with regard to their influence on the design of components?
  • What is an “offset yield strength” and for which materials is it used?
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Compression test

This article provides answers to the following questions, among others:

  • Why are no longish specimens used in the compression test?
  • Why is the true compressive stress lower than the engineering stress?
  • What is the difference between the “compressive yield strength” and the “compressive offset yield strength”?
  • What causes the formation of pressure cones in the material?
  • Why does a crack usually form at an angle of 45°?

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Hardness test

This article provides answers to the following questions, among others:

  • How is the hardness of materials defined?
  • On which principles are all hardness testing methods based?
  • Which indenter is used for Brinell hardness testing?
  • What is the load factor and what is it used for?
  • For which materials is Brinell testing particularly suitable?
  • Which indenter is used for the Vickers hardness test?
  • Under what conditions can Vickers hardness values only be compared with each other?
  • For which materials is Vickers testing particularly suitable?
  • Which indenters are used for Rockwell hardness testing and for which materials are they used?
  • What is the purpose of applying the preload?
  • What are the advantages and disadvantages of Rockwell testing?
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Flexural test

This article provides answers to the following questions, among others:

  • How does the flexural stress distribution in the cross-section of a specimen subjected to bend loading look like?
  • Where does the maximum bending stress occur?
  • What characterizes the “neutral axis”?
  • What role does the “axial section modulus” play in a bending load?
  • What is the “flexural yield strength”?
  • Why does the “flexural yield strength” has a higher value than the “tensile yield strength”?
  • For which materials is a “ultimate flexural strength” used instead of a “flexural yield strength”?
  • Why does the flexural test usually offer better results than the tensile test for determining the strength of brittle materials?
  • How can the modulus of elasticity (Youngs modulus) be determined?
  • How do residual stresses occur in the material?
  • Why does the neutral axis shift into the area of compression in grey cast iron?
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Charpy impact test

This article provides answers to the following questions, among others:

  • What are the objectives of the “Charpy impact test”?
  • Why does “notch impact energy” represent a measure of the toughness of a test specimen?
  • What external influences effect the notch impact energy?
  • What are “upper shelf”, “lower shelf” and “transition temperature”?
  • Which lattice structures show a pronounced upper shelf and lower shelf and which do not?
  • What is a ductile fracture, sliding fracture, brittle fracture and cleavage fracture?
  • How does the fracture speed influence the notch impact energy?
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Fatigue test

This article provides answers to the following questions, among others:

  • What are the objectives of the fatigue test and how is it carried out?
  • Why should the test frequencies not be set too high in the fatigue test?
  • What is a stress cycle?
  • How is the stress ratio defined?
  • What is the difference between alternating stress and pulsating stress?
  • What information can be obtained from the Wöhler curve?
  • What are the characteristics of “low cycle fatigue”, “high cycle fatigue” and “fatigue strength”?
  • Why does an increase of the mean stress in the compression range lead to larger bearable stress amplitudes?
  • What is the difference between “fatigue strength” and “fatigue limit”?
  • What are the characteristics of “alternating fatigue limit” and “pulsating fatigue limit”?
  • What are two typical characteristics of the fracture surface of a fatigue fracture?
  • What is the difference between “beach marks” and “fatigue striations”?
  • How can the fatigue strength of components be increased?
  • How to create the Haigh diagram and the Smith diagram and how can they be read?
  • How is the “rotating bending test” and the “reverse bend test” carried out?
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Stress rupture test (creep rupture test)

This article provides answers to the following questions, among others:

  • What is a hot yield strength?
  • What is creep?
  • What factors influence the intensity of creep?
  • At what temperatures is a technically relevant creep to be expected?
  • What is the difference between the “stress-rupture-test” and the “creep rupture test”?
  • What process do creep curves represent?
  • What statement do “creep limits” “and “creep strengths” provide?
  • Why are coarse-grained materials better suited than fine-grained materials for high-temperature applications?
  • What are the characteristics of primary, secondary and tertiary creep?
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Ultrasonic testing (UT)

This article provides answers to the following questions, among others:

  • What is the measurement principle behind ultrasonic testing?
  • What is the coupling agent used for?
  • How are ultrasound waves generated and received?
  • What is the difference between longitudinal waves and transverse waves?
  • What types of ultrasonic probes are used?
  • What is the dead zone?
  • Which probes are used for weld inspection?
  • What are phased array probes and what special advantages do they offer?
  • What is the minimum size of imperfections that can be detected by ultrasonic waves?
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Magnetic particle inspection (MPI)

This article provides answers to the following questions, among others:

  • What is the principle behind magnetic particle inspection?
  • How should flaws be aligned with respect to the magnetic field direction so that they are optimally visible?
  • Why are components tested both in the mode of magnetic field flow and in the mode of current flow?
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