Documentation:FIB book/Anthropomorphic Test Device (ATD)

Hybrid III family of ATDs

Introduction

Anthropomorphic Test Dummies (ATDs), also known as crash test dummies, are human-sized and -shaped, durable, instrumented devices used to determine the forces, accelerations, and deflections that would be experienced by a human in an injury scenario. These dummies are used in many industries and play a vital role in improving occupant safety in motor vehicles. ATDs are utilized in regulated crash tests to assess occupant safety and increase occupant protection (crashworthiness). The primary goal of these simulations is to reduce the number of fatalities and the severity of injuries caused by motor vehicle accidents. In the US, the Federal Motor Vehicle Safety Standards (FMVSS) 208 - Occupant Crash Protection administered by the US Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) specifies the performance requirements and safety limits for ATD acceleration and force to ensure adequate occupant protection during a crash.

Ideally, an ATD will be anthropometric (be the same size, shape, weight, and have the same overall external dimensions as the intended occupant), biofidelic (replicates human responses), and durable. It should also have simple instrumentation and yield repeatable results when tested. When manufacturing an ATD, it is important to consider the size, shape, mass, moment of inertia, stiffness, energy absorption, and energy dissipation properties of the dummy. These properties account for differences in age, size, and sex among humans. Another important consideration when designing an ATD is ensuring that it is appropriately built for the simulated direction of impact. To cover this wide spectrum of crash scenarios and subjects, ATDs are available with different physical characteristics and are specialized for a particular type of crash. It is not feasible to construct a single biofidelic ATD that is suitable for all types of impacts and crash scenarios. As such, to achieve optimal performance of the ATD, the type of crash defines the specific biofidelity and instrumentation that is required.

Keeping this in mind, the number of ATDs on that market has been increasing since the seventies. Presently, the largest manufacturer of ATDs (Humanetics Innovative Solutions, Inc., Plymouth, Michigan, USA) produces the Hybrid III family of dummies, which serve as the current gold standard for regulated frontal crash tests. This manufacturer also developed the Test device for Human Occupant Restraint (THOR), which is an ATD that was created to be more biofidelic than the Hybrid III.

Biofidelity

Liver injury biofidelity has been tested for abdominal inserts in some ATDs.

Specific ATDs

ATDs are typically designed and validated for one primary crash type, as it is difficult to create an ATD that is biofidelic in multiple situations.

Frontal

The two ATDs designed for frontal collision testing are the Hybrid III and the THOR ATD (Test device for Human Occupant Restraint).

Pregnant People

It is estimated that 130,000 people in the second half of pregnancy are involved in motor vehicle accidents each year, with between 300 and 3800 experiencing fetal loss due to the accident trauma . However, there seems to have been little development or research done to prevent this. Like many fields in medical research, the development of ATDs has been slow to represent and protect females, as such it is not surprising that the first pregnant female ATD was only developed in 1996 . In 2001, an updated version of the pregnant ATD was developed and named the Maternal Anthropometric Measurement Apparatus dummy, version 2B (MAMA-2B). This appears to be the most common pregnant ATD at this time.

Development and Design

Version 2B of the Maternal Anthropometric Measurement Apparatus (MAMA-2B), restrained in the test setup using a correctly positioned conventional seatbelt

In 2001 General Motors (GM), according to an agreement with the U.S. Department of Transportation, financed the development and evaluation of a new pregnant crash test dummy through the University of Michigan . Using epidemiological data, it was determined that smaller females face the worst outcomes in motor vehicle accidents. This is due to these individuals being seated closer to the steering wheel which is the primary point of impact with the abdomen in pregnant people. Likewise, worse accident outcomes have been observed closer to the end of the pregnancy. Due to these factors, the MAMA-2B ATD is built around a 5th percentile female Hybrid III and is designed to represent 30 weeks of gestation .

Using the structure of the Hybrid III 5th percentile female as a basis for the MAMA-2B allows for a significant reduction of development and production cost of the MAMA-2B ATD ; however, it also adds design complexity. During the design of the MAMA-2B, some modifications had to be made to the base Hybrid III such as removing parts of ribs 4 through 6, and a replacement pelvis had to be manufactured to allow for room for the fluid-filled bladder. Ensuring these modifications and construction of the MAMA-2B did not require specialized tooling was important to allow other companies to easily test with the MAMA-2B in the future .

To determine the size of the ATD uterus, data was taken from a 1999 study by Klinich et al., 1999 . Previously the best data on pregnant anthropometry was from abdominal depth measurements from 5th percentile Japanese pregnant people. These measurements were then scaled to fit the larger American population which is not a valid assumption . The size of the uterus is dictated primarily by the size of the fetus, and almost all newborns carried to full term are between 6 and 8 pounds, independent of the mother's stature or weight. By using more accurate data and the new fluid-filled abdomen, the MAMA-2B  has improved anthropometry with a more representative midline contour of 30-week gestation pregnant people in America.

To properly represent the pregnant abdomen, a fluid-filled bladder made of a silicone-rubber hybrid was developed. During development, eight iterations of the silicone-rubber hybrid were tested and improved on to ensure the ATD uterus had an appropriate mechanical response while still retaining durability to be used repeatedly .

Instrumentation

Types and locations of measurements made using the MAMA-2B dummy during sled tests

One of the primary goals of the MAMA-2B is to quantify fetal outcomes from a Motor Vehicle Accident (MVA). Placental abruption is thought to be the primary cause of fetal loss in MVAs; therefore, to assess the likelihood of a placental abruption, anterior and posterior pressure transducers were placed in the fluid bladder. Shape tape was initially going to be used to record the curvature of the fluid bladder, but it proved to not be accurate or repeatable enough to be used on the MAMA-2B. Future work to improve the reliability of the shape tape could be added which would provide important data about likely fetal outcomes. Furthermore, the chest potentiometer in the Hybrid III model also had to be removed due to the modifications to the ribs and chest, and interference with the fluid bladder .

Improvements to MAMA-2B

Since the popularization of the MAMA-2B, some modifications have been made to improve the sensors on the ATD. A 2005 study was able to add two IR-TRACCs (Infra-Red Telescoping Rod for the Assessment of Chest Compression), as well as two accelerometers which are aligned to record data for the Viscous criterion (V*C) calculation . With the viscous criterion the time and likelihood of soft tissue injury dependant on rate can be assessed. Additionally, the center of mass and proper seated position were defined. Continued research and improvement into the MAMA-2B and other pregnant ATD's is still needed to better protect pregnant people and improve fetal outcomes in motor vehicle accidents. This includes improving instrumentation, increasing biofidelity, and better characterizing the existing MAMA-2B's response . Adding the MAMA-2B or another pregnant ATD to the standard set of ATD's would also be a massive step to improving vehicle safety for pregnant persons.