# Probabilistic Analysis of Fatigue Behavior of Single Lap Riveted Joints
###### Abstract  
This research deals with the fatigue behavior of 200 small single lap multiple-riveted joint specimens, widely used for aeronautic structures. The tests were performed with three different levels of stress with stress ratio R = 0.05; three levels were set: 90 MPa, 120 MPa and 160 MPa. The fatigue life and critical crack size for all tested specimens were analyzed. According to the results' analysis, two types of fracture, through-hole and in proximity of the hole, were observed, depending on the level of stress: the higher the applied stress, the more through-hole cracking. Indeed, under the fatigue load with a stress level of 90 MPa, less than 30% of specimens showed cracks propagating through the hole, while, at the stress level of 120 MPa, the percentage reaches 36.3%. At the stress level of 160 MPa, 100% of specimens failed through the hole. Moreover, aimed to use experimental data for probabilistic methods, a statistical analysis was performed according to the Anderson-Darling test. This method allowed the analysis of the datasets, in terms of both fatigue life and critical crack size, providing information about the best distribution function able to fit experimental results. r 20 April 202011 May 202013 May 202020 April 202011 May 202020 April 202011 May 202020 April 202011 May 202020 April 202011 May 202020 April 20202011 May 202020 April 20202011 May 20202020 April 20  
consider, such as load level and frequency, micro-cracks due to drilling operation and manufacturing process, friction between the two fastened counterparts, etc. [9; 10; 11]. Nevertheless, some considerations can be nowadays performed thanks to the repeatability of fatigue tests proposed in the literature, also carried out on different materials. Most of the investigations showed that structural damages initiate in proximity of the notched zone and propagate due to the fatigue loading conditions [12; 13]. The experimental evidence shows the dependence of the fatigue life on the geometry of the jointed parts, on the rivet geometry and type, on the hole expansion caused by the rivet and on the load level and type [12; 14]. More in detail, the complex stress distribution caused by the hole expansion appears to have a significant influence on the crack initiation and, consequently, on the fatigue life [13]. Additionally, the different elastic spring-back of both rivets and clamped counterparts can cause refetting fracture under specific loading conditions. Moreover, [PERSON] and [PERSON] [15] demonstrated the effectiveness of a prediction model, based on crack growth, for the fatigue behavior of fuselage riveted lap joints. They also noticed how the portion of fatigue life spent in nucleating cracks is very small. Other critical aspects, such as corrosion should be considered to determine the fatigue life of such joints [12]. The fatigue behavior of riveted joints is also influenced significantly by the thermal load, especially for applications in the aeronautical field [16]. The complexity linked to the multiple design variables, which characterize such types of joints, gets complex the achievement of reliable fatigue life prediction models, especially through the analytical method. As a result, they are strongly empirical and often supported by numerical [8; 9] and probabilistic methods [17]. The achievement of reliable models represents, nowadays, an open field for the research community, since they could be used by designers for the improvement of their load-bearing capability, for the assessment of the fatigue life and for the scheduling of the inspection operations, aimed at monitoring the onset and the cracks propagation, according to the damage tolerance design approach. Since the high stress concentration around the fastener holes can facilitate the onset and the propagation of cracks under fatigue loading conditions, the maximum attention is paid on the drilling operations too. The most established fatigue criteria combine the fracture mechanics, the probabilistic and reliability approaches. [PERSON] et al.