13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- 2. Drop test: Perforation of 2024 T3 aluminum alloy sheets 2.1. Material Aluminum alloys are known for their high mechanical characteristics against their density. The 2024 T3 aluminum alloy (2024 AA) is used in aeronautical structural parts as planes' fuselage or wings. The process route of this precipitation hardening material, alloyed with copper, is well known: a casting, a homogenizing, a hot rolling, a solute heat treatment at 495°C, a water quench, a cold work to obtain higher strain, and to finish a natural aging. This is the T3 heat treatment [11]. The chemical composition of the 2024 aluminum alloy is presented in Table 1. Table 1. Chemical composition in %wt of the 2024 AA [12]. Al Cu Mg Mn Fe Si Zn Ti Cr Bal. 4.76 1.38 0.65 0.22 0.08 0.07 0.03 0.01 2.2. Experimental setup An instrumented drop test is used to perforate 2024 AA sheets (Fig. 1). A 5 kg test trolley slides on two bars from various height positions. Weights can be added to this trolley. Under the trolley a piezoelectric force sensor and a conical striker are fixed. This dynamic force sensor is calibrated for a range of validity from 0 to 100 kN and is used to measure the perforation force during impact with a relative error less than 5%. The striker is composed of a 60° conical nose and a 45 mm diameter cylindrical part. This cylindrical part is 10 mm long. A laser sensor (error of 0.5%) is used to measure the trolley’s displacement. Two high speed cameras are used to measure the striker displacement and to take picture of the sheet’s perforation. A mirror enables the observation beneath the sheet. Figure 1. Instrumented drop test. Twelve drop tests are performed to perforate a 2 mm 2024 AA sheet. The initial impact velocity and the striker total mass of each test are given in Table 2. If the striker perforates the sheet, values are in bolt font. The impact velocity evolves from 2.7 m/s to 6.9 m/s. The striker total mass is taken equal to 13 kg. The main objective is to find the ballistic limit velocity, to study the residual velocity and to analyze fracture and the force during impact.
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