## 1 Introduction
Results showed that, after the detonation, the propelled fragments impact the front surface of the panel at different velocities, angles of impact, and arrival times. The latter was found to be an influencing parameter in the initiation and the propagation of failure mechanisms in the different layers of the panel. It was also shown that the difference between the arrival time of the blast wave front and the arrival time of each one of the fragments aggravates the final damage caused to the multi-layered panel. [PERSON] et al. [14] suggested a simplified approach using experimental case studies to investigate the influence of the arrival time of blast and fragments on the dynamic response of a reinforced concrete (RC) element. Results showed that for both short and larger stand-off ranges, the fragment impacts and their arrival time with respect to the blast wave must be considered. [PERSON] et al. [15] investigated the detonation of bare charges next to heavy fragments. The fragments were projected onto reinforced concrete targets. It was shown that this technique of generating a combined loading highly influences the way in which the structure responds. They concluded that this is related to the difference in arrival time between the blast and the fragments at the target. [PERSON] et al. [16] supported the same conclusions. They demonstrated that the time interval \(\Delta t\) alters the dynamic behavior of the tested RC beams from low spallation to severe spallation or breach. [PERSON] et al. [17] demonstrated that, in addition to \(\Delta t\), both the SOD and the explosive charge mass have a significant influence on the RC slab damage mode. [PERSON] et al. [18] numerically investigated the damage caused to a storage tank subjected to the coupling effect of blast wave and fragment impact loading. The simulation results revealed that both the scaled distance and the arrival time of the fragment affect the storage tank damage. [PERSON] et al. [19] numerically investigated blast-driven fragments resulting from the detonation of spherical, cylindrical, and disk-shaped C4 explosive charges when projected inside a cylindrical tube. Although their computational model was able to predict the acceleration and the velocities of the blast-driven fragments, little focus was given to the influence of \(\Delta t\) on the dynamic behavior of the target. A more recent work by [PERSON] et al. [20] addressed this topic. They proposed a laboratory technique which uses a composite projectile to simulate combined blast and single fragment impact loading on an Aluminum target. They showed that \(\Delta t\) has a significant influence on the response mode of the Aluminum plate (plugging, dishing, cracking, etc.). [PERSON] et al. [21] shifted the focus and proved both experimentally and numerically the influence of charge shape and geometry on the velocity characteristics of an explosively driven single ball bearing and consequently on \(\Delta t\). They further investigated the momentum transfer mechanism from the charge to the projectile. These studies on the dynamic behavior of different materials and structures under the combined effect of blast wave and fragment impact loading improve our understanding of (i) the resistance of the different targets with respect to the combined loading, (ii) how the combined loading can be generated, and (iii) how the structures can be tested. The present paper studies the influence on \(\Delta t\) of the charge and the fragments characteristics (charge mass, projectile mass) and the stand-off distance from the center of the detonation to the target. Moreover it indicates how to establish a computational model in an attempt to better understand the momentum transfer from the charge to the projectile and its influence on \(\Delta t\). The present work is a part of a larger research effort to design a laboratory scale experimental technique to generate a reproducible combined blast and single or multiple fragment impact loading.