**Author details**

*New Challenges in Residual Stress Measurements and Evaluation*

traditional and consolidated approaches.

**evaluation**

specific applications.

sibility to perform in situ evaluation.

measurement.

is of capital importance but at the same time still not conveniently fulfilled by

**2. Current trends in residual stress experimental analysis and numerical** 

The importance, and at the same time, the complexity, of obtaining an accurate experimental evaluation of the residual stress inside a material has led, along the years, to the development of many different approaches. Some of them such as the hole drilling method (HDM) and X-ray diffraction (XRD) are, nowadays, mature and widespread techniques ruled by specific standards [4, 5]. Even if they can be considered as benchmark techniques, it should be taken into account that, in many situations, they have some inherent limitations that cannot be discarded in some

Hole drilling method, for example, cannot be conveniently used to determine the presence of residual stress too much far from the drilled surface. X-ray diffractometer is limited to the determination of superficial residual stress. Both the approaches cannot guarantee high surface resolution of the residual stress

More in general, it should be understood that each method developed for the residual stress evaluation has its specific advantages and drawbacks that make a specific approach appealing for a given application problem and inapplicable in some other situations. Having this in mind, however, it should be clear that current efforts are spent in the direction to increase the resolution of the measurement, both on the surface and in-depth, and to extend the capability to determine the residual stress present in the core of a given component. At the same time, also the development and improvement of nondestructive techniques for residual stress determination become of capital importance because this would expand the pos-

Additionally, a further challenge is in the direction of adopting less expensive equipment and to reduce, at the same time, the cost and the time required for a single measurement [6]. A final direction of evolution of the research in the residual stress field is toward the RS characterization at the micro- and nanoscale. This is of interest by taking into account that, when dealing with high cycle fatigue and very high cycle fatigue conditions, the damage accumulation occurs at the grain level. Moreover, the introduction of micro- and nanomechanical systems requires an enhancement of the capabilities of characterization over this range scale. In the direction of improving the on-surface resolution, it worth mentioning the great effort that was done in the last years in the development of the contour method [7] that allows obtaining a complete map distribution of the residual stress along the cut plane, but it is limited to materials that can be cut by EDM machine, and it exhibits a higher level of uncertainty close to the edges of the measured surfaces. Magnetic methods such as magnetic Barkhausen noise [8] and acoustic Barkhausen noise [9] can be adopted as well to obtain residual stress map on a component, and current efforts are spent in the direction of accurate calibration procedures that take into account other factors such as the hardness, the crystallographic nature, or the complexity of the stress field that can impact on the measurement. Nevertheless, their adoption is limited to magnetic materials. The problem of increasing the depth of evaluation of residual stresses can be conveniently afforded, for example, by implementing synchrotron X-ray diffraction or neutron diffraction [10]; in both cases, however, very expensive equipment is required as well as long-term planning of the experimental campaign to access to the dedicated facilities. As an

**4**

Caterina Casavola\*, Claudia Barile, Vincenzo Moramarco and Giovanni Pappalettera Dipartimento di Meccanica, Matematica e Management, Politecnico di Bari, Bari, Italy

\*Address all correspondence to: caterina.casavola@poliba.it

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