In vehicle structural parts, for example of aircraft, cracks may form, and this may lead to major damage to the point where the vehicle structure fails. Cracks in aircraft structures are generally due to a material weakening as a result of particular static or dynamic mechanical loads.
For example, a crack may also form and progress as a result of accidental damage to an aircraft structure in the form of scoring during improper maintenance. Accidentally produced damage of this type may be the starting point for subsequent crack formation or subsequent crack progression. It is therefore expedient to eliminate this damage resulting from repair measures, so as to avoid crack formation. However, cracks may also have other causes.
During maintenance, the damaged spots may be repaired by cutting out the entire area in which cracks have formed and replacing it with new material, which is inserted there or arranged above. In the case of scratches where it is expected that cracks will form starting from the scratches, the repair process may be carried out in the same manner as for crack repair. Replacing wing unit structures is time-consuming and leads to increased repair and operating costs. Material areas which are at risk of crack formation can be treated prior to use by laser shocking (laser shock hardening, laser shock treatment or laser shock peening). Laser shock peening, in the following also called laser shocking, is a method for producing an area of deep compressive residual stresses by processing the surface of a workpiece by laser shocking. Laser shocking conventionally uses beam pulses from pulsed lasers so as to transmit impact or shock waves onto the surface of a workpiece. By means of a plasma, the pulsed laser beam incident on the component surface from the laser beam source produces a strong local compressive force on a portion of the surface. In this context, at the point of incidence of the laser beam, below a closed liquid film, sudden removal or evaporation of a thin layer of this surface or of a coating (such as a metal adhesive strip or a coat of paint) leads to a plasma, resulting in an explosive force being produced. The compressive pulse from the rapidly expanding plasma emits a shockwave which migrates into the item. This compressive shockwave brought about by the laser pulse leads to deep local compressive deformations in the component. These local plastic deformations produce compressive residual stresses in the material. Laser shocking is disclosed in U.S. Pat. No. 3,850,698, titled “Altering Material Properties”, and in U.S. Pat. No. 4,401,477, titled “Laser Shock Processing”. During laser shocking, a strong local compressive force is transmitted onto part of the workpiece surface. Laser shocking is used so as to bring compressive residual stresses onto a workpiece, significantly increasing the resistance of the workpiece to a fatigue fracture. This application is disclosed for example in U.S. Pat. No. 4,937,421, titled “Laser Peening System and Method”.
DE 10 2008 044 407 A1 and US 2011/0290770 A1 disclose a method for irradiating an aircraft component having a damaged spot, which is carried out during maintenance on the aircraft. In this context, an area of the aircraft structural part close to the damaged spot is treated using a pulsed laser beam. Meanwhile, a compression wave passes through the irradiated area of the aircraft structural part and produces a compressive bias in this area. Thus, the propagation of new or existing cracks can be slowed in areas which are deemed critical.