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Developing Methods to Mitigate Blast Wave Effects

torso assemblyIn a jointly sponsored program (U.S. Navy Office of Naval Research and U.S. Army Natick Soldier Research, Development, and Engineering Center), APL has developed advanced head and torso surrogate models to support investigations of blast effects on the human body. With our instrumented human torso, we're evaluating the efficacy of body armor to protect warfighters against blast and ballistic impacts. The torso includes embedded sensors that quantify the amount of energy transmitted into the body, thus allowing us to measure the energy-absorption capabilities of the armor. This torso model has been tested continually under a wide range of traumatic conditions, including ballistic testing, shock tube testing, and open-field blast testing at the Army Research Laboratory. 

The success of the early model led to new funding for expanded efforts to study traumatic brain injury using an instrumented head model. We have also developed an instrumented head/brain to evaluate the protective capabilities of helmets.

The process for development of protocols for investigating the human response to blast loading includes:

  • Fabrication of human surrogate models,
  • Measuring response to blast loading (pressure, acceleration),
  • Determining the sensitivity, specificity, and durability of models, and
  • Creating computational simulations to predict response.

Joint Trauma Analysis and Prevention of Injury in Combat

APL is analyzing the processes for accumulating and synthesizing multiple-source and multiple-format forensic data on enemy engagements and combat casualties collected in theater. Sponsored by the Joint Trauma Analysis and Prevention of Injury in Combat program, APL staff are looking at the program's current processes to identify impending issues and recommend corrective measures to facilitate and standardize program products. This analysis leverages APL's experience in injury biomechanics, medical surveillance, and material science, among other relevant disciplines. This effort will culminate in improved tools to mitigate warfighter combat casualties, supporting the combatant commanders and material developers in the global war on terror.

Improving Warfighter Performance and Sustainment in Extreme Environmental Conditions

The Defense Advanced Research Projects Agency (DARPA) is sponsoring fundamental research efforts to enhance the level of warfighter adaptability to environmental extremes such as extreme heat, cold, and high-altitude hypoxia as a research area of the highest importance. Identifying molecular and physiological mechanisms underlying human adaptation is one of the prerequisites to achieving this goal. APL's approach to this problem, in collaboration with other researchers, is identifying key factors involved in all of these extreme environmental conditions. The objective is to understand these general mechanisms in order to increase the warfighters' adaptability and performance while being subjected to environmental extremes. Experimental results related to strengthening the heat-shock response have been promising.

Neurally Controlled Prosthetic 

To explore the potential for revolutionary changes in the design and natural performance of prosthetic limbs, in 2005 APL assembled a team of neural scientists, clinicians, technology developers, and commercial organizations. The program, sponsored by DARPA, is based on a highly aggressive engineering strategy to develop an entire limb system that meets stringent performance requirements. The goal is to achieve 22 degrees of freedom and a power-to-mass ratio over 600% greater than any existing comparable mechanical limb.

Vehicle Collision Studies

APL has a long-standing program in transportation research. Working with government agencies such as the Department of Transportation and the National Highway Traffic Safety Administration (NHTSA), we built and maintain a state-of-the-art laboratory to support vehicular safety efforts. We conduct rear-impact sled tests using a variety of anthropomorphic test dummies to better understand the response of automotive occupants during motor vehicle collisions. These tests provided critical data to the government in support of an upgrade to the Federal Motor Vehicle Safety Standard related to rear impact protection. To date, we have performed more than 250 sled tests using various crash test dummies. These efforts have supported improvements to the Federal Motor Vehicle Safety Standards. 

Neck Injuries Induced by Visual Augmentation Systems (VASs)

APL is developing techniques to assess the potential for injury caused by helmet-mounted night-vision systems. The approach is to define a standard procedure for measuring neck-torque-induced head-supported mass by

  • Developing a procedure for measuring the mass and center of gravity (CG) of current helmets and VASs measuring the mass and CG of CAD existing helmets and VAS helmet mounts
  • Creating a database of 3D CAD models that have the mass properties of currently fielded ballistic helmets and VASs
  • Comparing helmet and VAS mass property measurements with existing literature on neck injury

Biomechanical Survivability Systems

Warfighter Support

APL provides systems engineering support to the Army's Future Force Warrior Medical Systems Integration Team. The objective is to integrate the Army's Warfighter Physiological Status Monitor into the Future Force systems-of-systems architecture and thus bridge the gap between a prototype device and a fielded solution. The device monitors soldiers' physiology, including pulse, respiration, activity, and sleep deficit, to help determine their readiness, conduct remote triage, and monitor life signs of the wounded.

Developing Human Models for the Evaluation of Blast and Ballistic Threats

In the current battlefield environment, warfighters are constantly exposed to the threat of blast events and ballistic impacts. The exact mechanisms for injury from blast-related events are not well understood. To reduce the number of injuries sustained by warfighters, we need to know more about injury manifestation.

A team of APL investigators has developed computational and experimental models of the human head and torso to investigate the body's response to high-rate mechanical insults. These models are capable of predicting relative injury risk and evaluating the efficacy of existing and novel mitigation techniques. Simulated operational environments were created to evaluate the models and provide insight into the human body's response to high rate impact events. Complementary research efforts have developed miniaturized, high-frequency displacement sensors for in vivo organ placement and experimentally determined high-strain rate human tissue material properties for input into the computational models.


Human Torso Finite Element Model


Human Head Finite Element Model

Building a Military Relevant Shock Tube: APL's Contribution to Blast Injury Research

Use of explosive weaponry is the most common cause of both civilian and military combat casualties in terrorist incidents. Data from Operation Iraqi Freedom indicate that explosive devices account for at least 60% of deaths and over 70% of injuries in Iraq. Hence, blast injuries, especially blast-induced neurotrauma (BINT), have been called the signature wound of the war in Iraq. Blast-related injuries are anticipated as a continuing threat to both our troops and civilians; thus, the need for rapid advancements in mitigation and treatment technologies is even more critical.

The most recent experimental data suggest that the peak overpressure is not the most important injurious parameter of a shock wave, generated by either conventional explosives or enhanced blast weaponry (EBW), as previously thought. Thus, the duration of overpressure, the number of overpressure fronts and expansion waves, the difference between wavefront arrival times, and the interaction between waves emerge as potentially decisive factors for blast injury outcomes.

To clarify the importance of these factors and establish a causal relationship between them and the type and/or severity of injury, a strictly controlled experimental setting is required that would allow fine-tuning and grading of these shock wave properties. Our original shock tube design uses multiple, interchangeable tube sections of varying length and multiple membranes to formulate a well-founded concept for reproducing multiple wave fronts. The composite configuration enables use of both the open-end and closed-end modules to replicate complex shock wave signatures seen in theater. To our knowledge, no comparable design exists at this time.

Based on our design, we built a 6-inch-diameter compressed air-driven shock tube and have completed the standardization of the basic module. Currently, we are developing analytical and computational models, based on the physical shock tube parameters, to provide simulations guiding the design of a shock tube able to replicate the pressure response characteristics of operationally relevant blast threats. In addition, these computational techniques will allow us to predict the necessary shock tube characteristics for reproducing future specified threats of interest by sponsor organizations.

Establishing an artificially created analogous environment using a shock tube, we will be able to perform biomedical research concerning blast injuries, especially BINT, and develop new mitigation strategies and physical/mathematical models for injury prediction.

Basic configuration of the shock tube with a diaphragm separating the Driver and Driven sections. The tube is instrumented
with eight pressure sensors; two in the Driver section and six sensors (five static, one dynamic) in the Driven section.