# Failure Response of Simultaneously Pre-Stressed and Laser Irradiated Aluminum Alloys
## 1 Introduction  
The development of a general understanding for durability and damage analysis for structural components exposed to severe thermal heating is the most desirable knowledge in the defense and aerospace industry. In a broad range of load-bearing applications, for instance aircraft structures, lightweight structures, bridge decks, marine crafts and off-shore platforms, structural components may be subjected to severe thermal loading. The possible sources for the intense heating environment to preloaded components may be the aerodynamic heating, laser irradiation or localized intense fire [1, 2]. For example, when the work piece is clamped or the aircraft and missiles are flying at high speed, the specimen will be in the condition of external loading. In crash circumstances, automotive parts will face the load conditions where both high strain rate and rising temperature by adiabatic heating can be induced [3]. Structural reliability will be affected by the presence of thermal stresses, as well as the degradation of the strength properties at elevated temperatures caused by the heating. Since the modulus and yield stress of material generally decreases with the increase of temperature, material strength degrades under elevated temperature situations [4]. In general, dynamic failure processes are strongly influenced by the state of stress, the strain rate and loading history. The preloading or strain rate and temperature affect the material flow response significantly in deformation processes. Being subjected to quasi-static loading, strain hardening induces an enhancement in the force needed for thedeformation process, which may act as a stabilizing effect. In the case of dynamic loading, additional effects on the deformation process, for example on flow stress and the ductility of the material, may be experienced [5,6]. The understanding of thermo-mechanical behavior in a severe environment is essential to develop component design, product resistance to shock loading, for crashworthiness, safety and reliability in service performance assessment. There has been considerable work on understanding how structural metals deform under transient tensile conditions [7, 8, 9]. However, the research about the laser damage effect of aluminum and other structural materials under preloaded conditions is infrequent. Considering the combined effect of mechanical load and laser irradiation, a brief review of studies on aluminum alloys and other structural materials is presented here. [PERSON] et al. [10] investigated the effect of laser irradiation on the failure response of aluminum alloy (Al-7075) by using 3D digital image correlation and a series of thermocouples. The specimens were held under constant load and then irradiated by a diode laser (780 nm, 5 kW). The results exhibited non-uniform temperature and strain field distributions; moreover, the strain rate increased rapidly as the sample approached the failure point. The strength and failure response was also modeled and compared with experiments. [PERSON] et al. [11] presented an analytical model to find the failure threshold and to predict the thermal and structural behavior of aluminum alloys subjected to combined effects of laser exposure and mechanical loading. They employed a continuous wave (CW) CO\({}_{2}\) laser for irradiation under tensile or compression loading in the presence of tangential subsonic flow. It was observed that the combined laser exposure and mechanical loading considerably reduced the damaging threshold energy and room temperature tensile strength. [PERSON] et al. [12] had presented relationships between different parameters, such as laser power density, preload and the thickness on the failure time of the carbon fiber/epoxy composite laminates subjected to CW CO\({}_{2}\) laser. [PERSON] et al. [13] investigated the CW laser damage effect on a steel structure under preloaded invariable stretching stress. They attempted to develop the empirical relationships between the stretching stress and rupture temperature.