The deep hole-drill (DHD) technique is a mechanical measurement method used to determine principal residual stresses incrementally at depths several orders of magnitude deeper than what can be achieved with typical mechanical methods.
The DHD technique is useful for characterizing residual stresses from processes such as welding, heat treatment, casting, and forging in thick cross-sections. The technique can be used on metals and polymers. Materials that cannot be tested by X-ray diffraction, such as coarse grain or amorphous materials, can be tested with the DHD method.
How Does It Work?
The DHD method is based on linear elastic theory and involves drilling a reference hole into a test sample. Using the reference hole as a strain gage, the hole diameter is measured at various angular and depth positions using an air-gage system. The reference hole is then removed from the part through an over-coring process.
Residual stress relaxation caused by removing the reference hole from the part will cause a change in the reference hole diameter. The reference hole diameter is then remeasured at the same positions measured prior to the over-core process.
The change in diameter of the reference hole is used to determine the residual stresses incrementally over the length of the reference hole.
Deep Hole-Drill Features:
Features of DHD include:
- Measures residual stress in all directions parallel to the plane of the part’s surface
- Maximum measurement depth can be several inches depending on drill and air gage depth capacity
How are Lambda’s deep hole-drill services superior?
Lambda has developed specialized equipment, software, and procedures to perform DHD residual stress measurements. Lambda is a recognized leader in the field of residual stress measurement, with extensive experience testing all types of materials, including metallics, ceramics, and polymers of nearly any shape and size.
- We can test components in our laboratory or in the field
- All residual stress measurements are performed by our certified residual stress engineers and technicians
- Lambda does not subcontract residual stress testing to a third party
Questions about deep hole-drilling or other residual stress measurement needs?