Crashworthiness assessment considering the dynamic damage and failure of a dual phase automotive steel

Analyzing crash worthiness of the automotive parts has been posing a great challenge in the sheet metal and automotive industry since several decades. The present contribution will focus on one of the most urging challenges of the crash worthiness simulations, namely, an enhanced constitutive formulation to predict the failure and cracking of structural parts made from high strength steel sheets under impact. A hybrid extended Modified Bai Wierzbicki damage plasticity model is devised to this end. The material model calibrated using the experimental data covering high strain rate deformation, damage and failure successfully predicted the instability and subsequent response of the crash box under impact. Simulation results provide the deformation shape and deformation energy in order to predict and evaluate the vehicle crashworthiness. The simulations further helped in discovering the irrefutable impact of strain rate and stress state on the impact response of the auto-body structure. The strain rate is found to adequately affect the energy absorption capacity of the crash box structure both in terms of impact load and fold formation whereas the complex stress state has a direct association to the development of instability within the structure and early damage appearance within the folds

Seat Design for Crash Worthiness

A study of many crash deceleration records suggested a simplified model of a crash deceleration pulse, which incorporates the essential properties of the pulse. The model pulse is considered to be composed of a base pulse on which are superimposed one or more secondary pulses of shorter duration. The results of a mathematical analysis of the seat-passenger deceleration in response to the airplane deceleration pulse are provided. On the basis of this information, presented as working charts, the maximum deceleration loads experienced by the seat and passenger in response to the airplane deceleration pulse can be computed. This maximum seat-passenger deceleration is found to depend on the natural frequency of the seat containing the passenger, considered as a mass-spring system. A method is presented that shows how to arrive at a combination of seat strength, natural frequency, and ability to absorb energy in deformation beyond the elastic limit that will allow the seat to serve without failure during an airplane deceleration pulse taken as the design requirement

Analysis of Potential Co-Benefits for Bicyclist Crash Imminent Braking Systems

In the US, the number of traffic fatalities has had a long term downward trend as a result of advances in the crash worthiness of vehicles. However, these improvements in crash worthiness do little to protect other vulnerable road users such as pedestrians or bicyclists. Several manufacturers have developed a new generation of crash avoidance systems that attempt to recognize and mitigate imminent crashes with non-motorists. While the focus of these systems has been on pedestrians where they can make meaningful contributions to improved safety [1], recent designs of these systems have recognized mitigating bicyclist crashes as a potential co-benefit. This paper evaluates the performance of one system that is currently available for consumer purchase. Because the vehicle manufacturer does not claim effectiveness for their system under all crash geometries, we focus our attention on the crash scenario that has the highest social cost in the US: the cyclist and vehicle on parallel paths being struck from behind. Our analysis of co benefits examines the ability to reduce three measures: number of crashes, fatalities, and a comprehensive measure for social cost that incorporates morbidity and mortality. Test track simulations under realistic circumstances with a realistic surrogate bicyclist target are conducted. Empirical models are developed for system performance and potential benefits for injury and fatality reduction. These models identify three key variables in the analysis: vehicle speed, cyclist speed and cyclist age as key determinants of potential co-benefits. We find that the evaluated system offers only limited benefits for any but the oldest bicycle riders for our tested scenario

Development of an energy-absorbing passenger seat for a transport aircraft

Commercial air transport passenger safety and survivability, in the event of an impact-survivable crash, are subjects receiving increased technical focus/study by the aviation community. A B-720 aircraft, highly instrumented, and remotely controlled from the ground by a pilot in a simulated cockpit, was crashed on a specially prepared gravel covered impact site. The aircraft was impacted under controlled conditions in an air-to-ground gear-up mode, at a nominal speed of 150 knots and 4-1/2 deg glide slope. Data from a number of on board, crash worthiness experiments provided valuable information related to structural loads/failure modes, antimisting kerosene fuel, passenger and attendant restraint systems and energy absorbing seats. The development of an energy absorbing (EA) seat accomplished through innovative modification of a typical modern standard commercial aviation transport, three passenger seat is described

Energy absorption in polymer composite materials for automotive crash worthiness

The energy absorption capability of a composite material is important in developing improved human safety in an automotive crash. In passenger vehicles the ability to absorb impact energy and be survivable for the occupant is called the crash worthiness of the structure. The vehicle must be designed such that, in the event of an impact at speeds up to 35 mph with a solid, immovable object, its occupants do not experience a resulting force that produces a net deceleration greater than 20g. Subjection of the occupants to decelerations greater than 20g can cause serious internal injury, particularly brain damage. Energy absorption in these composite materials are dependent on many parameters like fiber type, matrix type, fiber architecture, specimen geometry, processing conditions, fiber volume fraction, and testing speed. Changes in these parameters can cause subsequent changes in the specific energy absorption of composite materials up to a factor of 2. Through ongoing research programs a considerable amount of experimental data on the energy absorption characteristics of polymer composite materials have been generated. They have been found to be efficient energy absorbers and suitable for crash worthy structural applications. But there are a lot of other criteria, in addition to a material being crash worthy, that need to be met before one can begin the use of a particular composite as a crash energy absorber in automobiles. Some of the primary ones being, low costs involved in their manufacture, the raw materials being readily available and many more. Once a composite material is identified to meet the above necessary requirements, one ought to study the effect all the controllable parameters (like fiber volume fraction, specimen geometry etc.) will have on its energy absorption capabilities, in an attempt to design the most crash worthy structure. The ACC (Automotive Composite Consortium) is interested in investigating the use of chopped fiber reinforced composites as crash energy absorbers primarily due to the low costs involved in their manufacture thus making them cost effective for automotive applications. While many scientists have investigated the energy absorption characteristics in various continuous fiber reinforced composite materials, there is no literature available on the energy absorption and crushing characteristics of chopped fiber reinforced composite materials. Therefore the primary goal of this project was to determine the crash worthiness of a chopped carbon fiber composite material system and to see how it compared with that of other fiber resin systems like graphite/epoxy cross-ply laminates, a graphite/epoxy braided material system and a glass-reinforced continuous strand mat (CSM). To meet this goal first an experimental set up was developed for discerning the deformation behavior and damage mechanisms that occur during the progressive crushing of composite materials. The composite material systems studied were chopped carbon fibers reinforced in an epoxy resin system, graphite/epoxy cross-ply laminates, graphite/epoxy triaxial braids with 0/+30°/-30° fiber orientation and glass/polyurethane continuous strand mat. Quasi-static progressive crush tests were then performed on these composite plates to identify and quantify their energy absorbing mechanisms. An attempt was made to understand in great detail the effect of various material (fiber volume fraction, fiber length, fiber tow size) and test (specimen width, loading rate, profile radius, constraint condition) parameters on their energy absorption capability by varying these parameters during testing. After having identified which combination of fiber volume fraction, fiber length, fiber tow size and specimen width will yield the highest energy absorbing material, the quantity of this material needed to ensure passenger safety in a mid-size car traveling at various velocities was calculated. The specific energy absorption, SEA, of the chopped carbon fiber composite material, CCF, was the highest compared to that of all the other composites investigated herein. The 2 inch wide specimens belonging to panel group CCF5 having fiber tow size 150 gsm (grams per square meter), a fiber length of 1 inch and 50% fiber volume fraction recorded the highest SEA equal to 28.11 kJ/kg when tested at 5 mm/min crushing speed under the tight constraint condition using a profile block of radius 0.635 cm. It was calculated that only 4.27 kg of it would need to be placed at specific places in the car to ensure passenger safety in the event of a crash at 35 mph. This clearly led to an important practical conclusion that only a reasonable amount of this composite material is required to meet the necessary impact performance standard. The CCF composite tested at 5 mm/min crushing speed met both the criteria that need to be satisfied before a material is deemed highly crash worthy: A high magnitude of energy absorption and a safe allowable rate of this energy absorption. All the experimental data and test observations generated from the above work was used to support the modeling efforts conducted by the Computer Science and Mathematics division at ORNL in their pursuit to develop analytical material damage models

Cluster-Based Optimization of Cellular Materials and Structures for Crashworthiness

The objective of this work is to establish a cluster-based optimization method for the optimal design of cellular materials and structures for crashworthiness, which involves the use of nonlinear, dynamic finite element models. The proposed method uses a cluster-based structural optimization approach consisting of four steps: conceptual design generation, clustering, metamodel-based global optimization, and cellular material design. The conceptual design is generated using structural optimization methods. K-means clustering is applied to the conceptual design to reduce the dimensional of the design space as well as define the internal architectures of the multimaterial structure. With reduced dimension space, global optimization aims to improve the crashworthiness of the structure can be performed efficiently. The cellular material design incorporates two homogenization methods, namely, energy-based homogenization for linear and nonlinear elastic material models and mean-field homogenization for (fully) nonlinear material models. The proposed methodology is demonstrated using three designs for crashworthiness that include linear, geometrically nonlinear, and nonlinear models

Test Methods for Composites Crashworthiness: A Review

Crashworthiness is a material\u27s ability to absorb energy during a vehicle crash. Modern automobiles, aircraft, rail vehicles, and marine vessels incorporate crashworthy structures. The use of composite materials, with their high specific strength and stiffness, can result in efficient and safe vehicles. Mechanical testing is essential for obtaining a deeper understanding of the crash-worthiness capabilities of composite materials. This review highlights the many aspects involved in crashworthiness testing of composites, including a brief overview of the field of crashworthiness, general crushing behavior, typical testing methodologies, and the effect of the loading rate and friction on test results

The Reliability of Autonomous Vehicles Under Collisions

Unmanned autonomous vehicles (UAV) subject is one of the most conspicuous topics of the last decade ensures a better handling ability for more precision way of control of the system or the drive compared to the human. Focusing this issue causes the more computerized vehicles the less unacceptable mistakes. Notwithstanding the efficient drive parameters are increased, the collisions are still the worst scenarios for the vehicles that should be taken care of. The most reliable way to define the collision response of the vehicles and the occupants is crash tests, although it is time consuming. Except crash test is the most convenient procedure to define the details of the impact process; it is also the most expensive way even for the major companies and research centers. Considering the compelling pricey amount of the first investment of the crashworthiness facilities and the crash test costs, recently, computer-aided simulations with the finite element method (FEM) using an explicit dynamics approach is very convenient, especially for the transient dynamic analysis. This chapter characterizes some perspectives of the autonomous vehicles in a short glance of an enormous science of the collisions with the help of experimental and numerical approaches