Code of Federal Regulations Title 49. Transportation § 49.587.17 Construction

(a) The main honeycomb block is bonded to the backing sheet with adhesive such that the cell axes are perpendicular to the sheet. The cladding sheet is adhesively bonded to the front surface of the main honeycomb block. The top and bottom surfaces of the cladding sheet are not bonded to the main honeycomb block but are positioned close to it. The cladding sheet is adhesively bonded to the backing sheet at the mounting flanges. The bumper element honeycomb is adhesively bonded to the front of the cladding sheet such that the cell axes are perpendicular to the sheet. The bottom of the bumper element honeycomb is flush with the bottom surface of the cladding sheet. The bumper facing sheet is adhesively bonded to the front of the bumper element honeycomb.

(b) The bumper element honeycomb is divided into three equal sections by means of two horizontal slots. These slots are cut through the entire depth of the bumper element and extend the whole width of the bumper. The slots are cut using a saw;  their width is the width of the blade used which do not exceed 4.0 mm (0.16 in).

(c) Clearance holes for mounting the deformable face are drilled in the cladding sheet mounting flanges (shown in Figure 5). The holes are 20 mm (0.79 in) in diameter. Five holes are drilled in the top flange at a distance of 40 mm (1.57 in) from the top edge of the flange and five holes in the bottom flange at a distance of 40 mm (1.6 in) from the bottom edge of the flange. The holes are spaced at 100 mm (3.9 in), 300 mm (11.8 in), 500 mm (19.7 in), 700 mm (27.5 in), 900 mm (35.4 in) horizontally, from either edge of the barrier. All holes are drilled within ±1 mm (0.04 in) of the nominal distances.