WEBVTT 00:00:05.617 --> 00:00:11.617 Hi, I'm Allison Nelson and today I'm going to be talking about combat helmet performance and mitigating blast loading on the head. 00:00:13.138 --> 00:00:21.138 So use of explosive weapons in military conflicts has grown over the last century, which has led to an increase in traumatic brain injuries caused by blast events. 00:00:20.995 --> 00:00:25.995 This has brought the conversation of combat helmet blast protection effectiveness to the forefront. 00:00:25.576 --> 00:00:36.576 Current infantry combat helmets offer fragmentation, ballistic, and impact protection, but none of them are currently designed for protection against primary blast, despite often being worn in a blast environment. 00:00:37.612 --> 00:00:46.612 Previous numerical simulations have suggested that the blast tape infiltrates the gap between the head and helmet and generates regions of increased pressure on the surface of the head. 00:00:46.687 --> 00:00:55.687 And this phenomenon was termed the underwash effect. And while it's been reproduced with computational models, there are limited studies actually evaluating this effect experimentally. 00:00:55.733 --> 00:01:03.733 So the objective of this work was to empirically investigate the effect of the combat helmet and orientation on blast loading on the head surface. 00:01:04.512 --> 00:01:08.512 We hypothesize that the surface pressures will be increased with the helmet, especially at the back of the head. 00:01:08.890 --> 00:01:13.890 Since it's been predicted that the blast pressure occurs on the side opposite of the blast source. 00:01:13.797 --> 00:01:20.797 And then in the 45 degree rotated orientation, we expect the pressures to be increased at all locations under the helmet. 00:01:21.809 --> 00:01:27.809 To accomplish this, we created an instrumented head form with a human skull model affixed to a hybrid 3 crash dummy neck. 00:01:27.631 --> 00:01:34.631 And this head form was secured in our advanced loss simulator, either fully facing the blast, which is the zero degree orientation. 00:01:35.471 --> 00:01:43.471 Or rotated 45 degrees about the transverse axis, which essentially positions the head form facing upwards but still towards the blast. 00:01:43.881 --> 00:01:50.881 We also considered a helmet or no helmet case in which the helmet was either on or off of the head form. 00:01:51.135 --> 00:01:57.135 And then our large advanced loss simulator was used to expose the head form to a blast pressure of approximately 16 psi. 00:01:56.958 --> 00:02:04.958 And we did three tests for each combination of experimental conditions, which included for the zero degree rotation, a no helmet and helmet case. 00:02:05.158 --> 00:02:09.158 And for the 45 degree rotation condition, a no helmet and helmet case. 00:02:11.401 --> 00:02:19.401 We also instrumented our head forms. With four pressure transducers, one in the forehead, one in the skull front, skull back, and then the skull side. 00:02:20.536 --> 00:02:26.536 The school side was located approximately above the ear and the forehead front and back were located right along the middle of the skull. 00:02:27.177 --> 00:02:46.177 We also instrumented our advanced blast simulator with wall sensors and a pitot probe, but primarily we're going to be focused on wall sensor two, which is located directly above where the head form was positioned in the blast chamber We conditioned and acquired all of our signals with a TMX multi-channel high-speed data acquisition recorder 00:02:46.141 --> 00:02:58.141 And we sampled at 800 kilosamples per second. We collected pressure data during these tests and were primarily interested in the peak pressure, which is the maximum pressure And the pressure time curve. 00:02:58.481 --> 00:03:06.481 And then impulse, which is the area under that pressure time curve. And that takes into consideration the overall pressure as well as the duration of the blast event. 00:03:06.998 --> 00:03:12.998 And the frontal orientation, we found that the peak pressure was actually reduced at the forehead and top front of the head. 00:03:12.957 --> 00:03:24.957 But it was increased at the back and side of the head. So this can be visualized here, the zero degree rotation Results are located on the left and we have our no helmet case on the left here and then 00:03:24.859 --> 00:03:34.859 Our helmet case on the right. And you can see the reduction with this representative pressure trace of the blue here is the forehead. So we see reduction with the helmet. 00:03:35.117 --> 00:03:40.117 But in contrast, we see with the orange, it actually increases with the helmet. 00:03:41.594 --> 00:03:55.594 And now just to better visualize this, I have the averages included in these bar plots below. And so we can see that we're getting approximately the same pressure with the No helmet case, which is a solid line in our helmet case, which is checkered. 00:03:56.081 --> 00:04:06.081 But we're seeing a decrease in pressure with the helmet at the forehead and the skull front, but we're actually seeing an increase at the skull side and especially at the skull back. 00:04:06.040 --> 00:04:13.040 And for the total impulse, we're actually seeing an increase in impulse across all locations. 00:04:12.785 --> 00:04:23.785 So in the 45 degree rotation. We actually see that the helmet case resulted in notably greater pressures at all sensor locations compared to the no helmet case. 00:04:24.424 --> 00:04:33.424 So this is shown in our representative plots here. But it's also shown in our bar plots where there's a dramatic increase between the no helmet and helmet case. 00:04:33.972 --> 00:04:40.972 The same was true for the total impulse, where all were greater, but it's much more exaggerated in the 45 degree rotation orientation. 00:04:42.142 --> 00:04:53.142 So a limitation of this work is that the biofidelity of the head form is lacking a bit as it does not model the soft tissue of the scalp, and this could reflect the shockwave reflections on the head surface. 00:04:53.230 --> 00:05:03.230 Though it would likely be minimal. We also consider the head form in isolation, meaning without a torso. So that could affect how the pressures are getting up and under the head form. 00:05:02.705 --> 00:05:08.705 However, these findings essentially suggest that the underwash effect was observed experimentally. 00:05:09.438 --> 00:05:16.438 And the combat helmet does offer some reduction in peak pressure towards the front of the head, but peak pressure and impulse were predominantly increased with the helmet overall. 00:05:16.507 --> 00:05:23.507 And then in future directions, we want to consider how does this increase loading actually translate into injury? 00:05:24.036 --> 00:05:28.036 And would different pad geometries help mitigate this increased pressure under the helmet?