| dc.description.abstract | This thesis reports results of experimental and numerical work on the impact response of industrial helmets subjected to severe impact loading. The impact is produced by accelerating a load transfer bar on to the helmet by making use ofan air gun apparatus. A special test rig is provided; using the test set up, the incident stress transmitted into helmets were calculated by using a two-gage method. The method is based on the propagation of the tensile stress waves reflected from the free ends afler impact by utilizing a modified Hopkinson pressure-bar technique. To obtain the impact response of helmet at any position, a numerical calculation using MSC/NASTRAN 3D were conducted. Solidwork 2001 3D software was used to model the helmet: two type of helmet model were introduced, they are (a) plain model, and (b) with longitudinal rib model. The incident stress is introduced on the top center of the crown. The intensity of the incident stress introduced at that location is 19.65 MPa, as it is found from the result of the experiment. The mean value of the incident stress obtained from the impact experiment is used as elemental pressure input in the FEAt model. It is well known that the effect of impact loading on the structure is different from that ofstatic loading. Under impact, the stress wave may be propagated and is reflected at free boundaries toward the impact location. The waves may interfere each other and form a stress concentration zone that may detoriate the structure. In case of the helmet structure reported in this thesis is worth to note that for all cases the tensile stress in x (?x) direction concentrate on the front direction and in y (?y) direction exhibit on the side of the structure. And longitudinal rib may decrease the tensile stress in x (?x) direction. The impact response ofplain helmets are different from those of helmets equipped with longitudinal rib. The effect oflongitudinal rib may decrease the ?x significantly at the front ofthe helmets and it has no significant contribution in reducing ?y . | en_US |
