Intro to Vehicle Crashworthiness Expert Overview

Vehicle crashes occur for countless reasons, and thankfully most do not result in substantial injury. When functioning properly, modern vehicle safety systems allow occupants to walk away from crashes that may have been fatal twenty years ago. Advanced vehicle structures and restraint systems have become the industry norm.

In this article, automotive engineer, Christopher Roche, provides an introduction into the science and principles of vehicle crashworthiness.

The Science and Principles of Vehicle Crashworthiness

Vehicle crashworthiness is the science of focusing on protecting occupants involved in frontal, side, rear, and rollover accident events through the utilization of various safety systems and safety principles. These include:

1. Minimize crush to maintain survival space
2. Provide proper restraint throughout the entire accident event
3. Prevent ejection from the vehicle and nominal seating positions
4. Distribute energy and dissipate crash forces
5. Prevent post-crash fires

Crashworthiness safety systems must work together to provide adequate occupant protection throughout an entire accident. These safety systems are akin to safety links in a chain. If one link fails, then the safety chain has failed.

Cause of Crash vs. Cause of Injury

Crashworthiness safety systems do not prevent accidents from occurring. Instead, they prevent or minimize the risks of serious injury or death once an accident has occurred.

If all accidents could be eliminated, there would be no need for safety systems that help prevent or minimize injuries after an accident has happened. Hence, there is a distinction between the cause of an accident versus the cause of an injury.

Whether a vehicle was designed with features to ensure the safety of its occupants in a foreseeable accident requires an investigation of the vehicles’ crashworthiness.

Vehicle Structures

Modern vehicle structures are designed from the outset for crash events. These structures can be divided into two types based on their primary crashworthiness function: crushable structures or safety cage structures.

Vehicle Crushable Structures

For a standard two-row vehicle, the crushable structure will consist of body and chassis parts that are forward of the front dash and those rearward of the second-row seats.

These structures are engineered to collapse, crush or bend in a repeatable manner and absorb or dissipate crash energy while doing so. The crushable structure at the front is designed to control the rate of deceleration experienced by the occupants in a frontal crash and to enable the restraints system to be effective.

These structures work in conjunction with seatbelts and airbags to slow occupants over the longest possible time and distribute crash forces over the largest area possible. When these systems function correctly, they effectively decrease the loads exerted upon occupants in a crash and reduce the severity of any resulting injury.

Vehicle Safety Cages

For the same two-row vehicle, the safety cage structures are designed to minimize intrusions into the occupant survival space. They also support the crushable structures and provide load paths.

The safety cage consists mostly of body structure parts that surround the occupants, such as the A, B and C pillars, the roof rails, side sills or rocker panels, crossmembers, roof headers and door impact beams.

Manufacturers use different strength materials to optimize the performance of the structure based on the crash requirements. In the illustration, the different colors represent different grades of steel with varying strengths.

The highest strength steels are used in the safety cage structure. Lower strength steels are used for the crushable structures or areas where stiffness or other performance requirements are the priority.

By selectively incorporating a range of different strength materials throughout the design, manufacturers can balance safety and weight concerns and build vehicles that are both safe and efficient.

Shaped for Crashworthiness

The picture above is a front frame rail tip on a newer light truck. The shape may seem arbitrary to the untrained eye, but the “rippled” area is a crush initiation zone.

The formations in the metal create a weaker area than the straight rails; when a longitudinal load is applied to the rail, such as in an impact, the rail will collapse in this area first. This ensures that the same area of the rail collapses first and in turn promotes the desired collapse behavior of the entire rail to maximize energy absorption and dissipation. These crush initiating zones are carefully engineered, optimized virtually with computer simulation, and verified through physical crash testing.

With the deliberate design and tuning of these areas of the crushable structure, they can be susceptible to interference with aftermarket items such as tow hooks, push bars, grill guards and lift kits.

Without proper engineering analysis on the location of the mounting hardware, it is foreseeable that aftermarket alterations may cause the rail to crush in an undesirable pattern and even cause the impact sensors to not properly detect the magnitude and direction of collision forces, resulting in the incorrect deployment of the airbags.

Vehicle Crash Expert Witness Investigations

From complex crash reconstruction to developing demonstrative evidence for court testimony, the transportation experts at Robson Forensic are well equipped to assist in your investigation. Our experts have in-depth knowledge of how gasoline and electric vehicles are designed and built, they are fluent in the regulations affecting trucking operations, and have designed, built, and maintained our nation’s transportation infrastructure.

For more information, submit an inquiry or call 800.813.6736.

Featured Expert

Christopher D. Roche

Automotive Engineer & Crash Expert

Christopher Roche is an automotive engineer with nearly 30 years of professional experience working for major vehicle manufacturers, specializing in the design of vehicle structures to protect… read more.