*Article* **The E**ff**ect of Laser Peening without Coating on theFatigue of a 6082-T6 Aluminum Alloy with a Curved Notch**

### **Enrico Troiani and Nicola Zavatta \***

Department of Industrial Engineering, University of Bologna, 47121 Forlì, Italy **\*** Correspondence: enrico.troiani@unibo.it

Received: 20 May 2019; Accepted: 26 June 2019; Published: 28 June 2019

**Abstract:** Laser shock peening has established itself as an effective surface treatment to enhance the fatigue properties of metallic materials. Although a number of works have dealt with the formation of residual stresses, and their consequent effects on the fatigue behavior, the influence of material geometry on the peening process has not been widely addressed. In this paper, Laser Peening without Coating (LPwC) is applied at the surface of a notch in specimens made of a 6082-T6 aluminum alloy. The treated specimens are tested by three-point bending fatigue tests, and their fatigue life is compared to that of untreated samples with an identical geometry. The fatigue life of the treated specimens is found to be 1.7 to 3.3 times longer. Brinell hardness measurements evidence an increase in the surface hardness of about 50%, following the treatment. The material response to peening is modelled by a finite element model, and the compressive residual stresses are computed accordingly. Stresses as high as −210 MPa are present at the notch. The ratio between the notch curvature and the laser spot radius is proposed as a parameter to evaluate the influence of the notch.

**Keywords:** laser shock peening; fatigue; notch; aluminium alloys; finite element method
