Ultra-high molecular weight polyethylene (UHMWPE) plates are extremely effective against small calibre ballistic threats. The composite nature of such structures implies a complex mechanical response at impact, involving phenomena such as delamination, ply splitting, fibre-matrix debonding and shear and tension failure of the fibres. However, in the process of impactor kinetic energy consumption, the thick composite plates exhibit two phases: the first phase characterised by shear failure of the fibres, and a second phase when the impactor creates a bulge by deflection and bending of a sub-laminate, which eventually can be completely detached from the rest of the board [1]. In this study, we propose one experimental setup to assess the values of the loads that cause the sub-laminate detachment in plates made of Dyneema HB26. The test is based on pre-notched plates, used to stimulate the occurrence of delamination of sub-laminate on an area delimited by the notches. The depth of the notches controls the thickness of the sub-laminate strip. A central area of 40 x 40 mm is impacted with a flat-head projectile of 0.55 kg, Figure 1 (left), at the base of which was attached a PCB 350C03 accelerometer. The 150 x 150 x 10 mm plates were fixed in a test rig by butterfly head screws. Following the tests, the strips were completely delaminated, Figure 1 (centre), starting from the central part towards the edges, the deceleration suffered by the projectiles being recorded with the help of the accelerometer, Figure 1 (right). The delaminated surface was about 4400 mm2. The projectile energy loss through detachment of the strip was found to be sensitive to the strip thickness: from 10.8 J for 2 mm to 21.3 J for 4 mm. The same dependency was observed in the case of the maximum deceleration of the projectile, attained in the first sequence of the impact/detachment process.