Material modeling and analysis to select artificial materials for simulating human head.
Instrumentation of the head model to record and analyze blast response.
Validate experimental blast response data with the developed mathematical model.
High-Speed Video Imaging
This video, taken by the Aramis High-Speed Cameras, shows the RED Head being subjected to a blast in the shock tube to generate data that helps map pressure histories in the head. The data recorded from experiments like this one is crucial to the Trauma Mechanics Research Initiative. It provides a basis for our understanding of the movement of blast waves through the human head.
PDMS Skin Simulant
The RED Head has a two-piece skin made of polydimethylsiloxane (PDMS) – a silicone-based organic polymer. The larger part of the skin covers the cranium, face, and neck, and it is attachable/detachable over the one-piece skull. The smaller part of the skin is glued at the back of the skull covering mostly the occipital bone area.
The average thickness of the skin is 7 mm, which is consistent with the 5-7 mm scalp thickness for a real human head. The skin was painted with white spray paint and marked with black dots. This enables three dimensional displacement measurements of the head using high-speed, high-resolution ARAMIS® video system.
The skin material went through dynamic mechanical analysis (DMA) where the storage and loss modulus were plotted against frequency. Ultrasonic vibration analysis was also performed to find material properties for up to 10 MHz frequency.
The initial version of the head model was prepared from dense urethane foam having two pieces of skull approximately symmetric about the sagittal plane. The skull material properties were not perfectly matched to the desired values, but the geometry was very much like a real human skull. However, a two-piece skull is not good for testing because the seam between the two parts would change how the shock waves propagate under blast loading. Also, the skull needs to be clamped from behind, which is not consistent with a human head that is supported by the neck from below. Due to these limitations, a new skull model was prepared to be used in the next version of the RED Head.
A one-piece skull design offers more consistency in the propagation of shock waves through it and into the brain model. This skull has a stainless steel base plate which can be bolted into the bottom of the skull. The plate contains a silicone rubber gasket to offer resistance against fluid leakage. This is an advantage because of the possibility to insert cerebrospinal fluid simulant inside to better emulate a real human head. Another feature of the base plate is that it can be connected to a flexible neck structure, something common in crash test dummies. Incorporation of such a neck structure gives the head flexibility when impacted by a shockwave.
Brain Simulant and Mold
The brain consists of several parts, each of which have unique mechanical and viscoelastic properties. Simulating such detail is very complex so it was decided to prepare the brain out of a single homogeneous material. With this constraint, the part of the brain containing the largest volume of tissue was considered as the one to be simulated by a synthetic material. To choose the materials, general properties of brain cortex were considered. DMA analysis was performed on gelatin and silicone gels, and these properties were compared with those for a real brain as obtained from literature. Finally, a specific silicone gel was chosen as the brain simulant material. The property of the gel can be varied by adding a "thinner," which offers control over the brain simulant's properties.
Brain Mold Preparation
Geometry of the brain layer is significant to the model's simulation capabilities
Silicone rubber was used as the brain mold
A full-scale demonstration model of human brain was used
Mold preparation was done in the sculpture facility of the Arts Department at UNL
Fiber optic sensors
All-glass sensor, at the tip of the optical fiber
Fully biocompatible with high measurement resolution and precision in detecting very quick and subtle pressure variations
Piezoelectric pressure sensors
National Instruments PXI
FISO Veloce 50 signal conditioner, 200 kHz sampling rate
National Instrument’s LabViewRT Server
National Instrument’s LabView 2009
The RED Head or "Realistic Explosive Dummy Head" development focuses on head injuries caused by shock waves generated by explosions. This head surrogate model is developed by selection of appropriate syntetic materials to emulate properties of human head components, i.e. skin, skull and brain. The geometries of these components are carefully controlled to replicate biometrics of human head. The model is instrumented with various sensors to capture the load caused by shock waves.