Experimental Residual Stress Analysis

Residual stresses are those mechanical stresses that occur in structural parts and materials but cannot be traced back to external operating loads. The causes of such internal stresses are manufacturing processes such as casting, welding, heat treatment or mechanical processing.

In many cases, these process-related stresses are of decisive importance for the behavior of components regarding their operational safety. The problem stems from the fact that internal and operating voltages often overlap in an unfavorable manner and lead to damage without the component's intended load limit being reached. It is therefore obvious that quantitative information about the size and direction of these residual stresses determine the operational safety, quality, and performance of the component. Knowledge of the residual stress state is a prerequisite for clarifying the causes and evaluating the influence on the operating behavior.

The determination of residual stresses is carried out using experimental methods. Over the last few years, numerous procedures have been developed which differ depending on the tasks. Mechanical or radiographic processes are used. Our aim is to create components with optimized residual stress for our customers.

Experimentelle Eigenspannungsanalyse octogon

 

MECHANICAL HOLE DRILLING METHOD

The hole drilling method can be classified between destructive and non-destructive measurement methods. The incision in the component to be examined is kept small so that the load-bearing capacity is not impaired.

A special strain gage rosette is applied to the component to be examined and a small blind hole is then drilled through the center of this strain gage rosette. This special strain gage measures the deformations (rebound) at the drilled hole that result from the released internal stresses. The specially developed strain gage rosettes have three individual measuring grids arranged in relation to one another to simplify the exact positioning of the drill. The blind hole for releasing the residual stresses usually has a diameter of just a few millimeters and is made either at a slow cutting speed (HSS face mill) or with the help of high-speed compressed air turbines with a hard metal end mill. The detection of the expansion by means of the hole drilling method is carried out step by step, with the resulting measurement data being used to calculate the residual stresses over the drill depth and the total expansion.

RESIDUAL STRESS MEASUREMENT BY HOLE DRILLING METHOD

  • Customer supplied parts (e.g. machine part, vehicle part, etc.)
  • Clarification of the points at which residual stresses must be determined
  • Definition of the strain gage (DMS) application points
  • If necessary, mechanical adaptation of the components (creation of a 3D CAD model)
  • Selection of the strain gages, considering the component material and the environmental conditions
  • Execution of the strain gage application and interconnection
  • Interconnection with measuring amplifiers according to customer requirements
  • Calibration of the sensor with a calibration device specially developed for the application

Bohrlochmethode octogon

 

RADIOGRAPHIC PROCEDURE 

We prefer the radiographic procedure using X-ray diffraction (XRD) for residual stress measurements close to the surface. The radiographic determination of residual stresses is based on the principle of diffraction of X-rays at the lattice planes of a crystalline material. The basic idea of the X-ray stress determination is to determine the changes in the lattice plane spacing that occur in an elastically stressed material compared to the stress-free state. The strains determined can be converted into stresses using the appropriate elasticity constants.

This procedure is only suitable for crystalline materials. The X-ray radiation used has a low penetration depth, this way a high depth resolution is achieved. Larger depth ranges can be achieved by step-by-step electrochemical removal with subsequent measurements.

RESIDUAL STRESS MEASUREMENT BY RADIOGRAPHIC PROCEDURE (XRD)

  • Detailed analysis of the material provided by the customer
  • Detailed input documentation
  • Determination of interesting measurement positions
  • Specification of the residual stress directions to be measured
  • Electrochemical depth removal
  • Reference measurements
  • Meaningful summary of the results

XRD octogon

 

Services

In cooperation with our partners we realize the economical and reliable determination and evaluation of the residual stress state of your components. The efficient selection of the analysis method adapted to the client's problem results in an economical measurement strategy. Our equipment enables residual stress investigations on difficult component geometries and on a wide range of materials. Our experienced staff creates an economically and effectively analysis, allowing you a profound decision-making. In addition to a meaningful result protocol, our scope of services also includes detailed input documentation of your component.