<div>Thin walled tubular structures are widely used in the automotive industry because of its weight to energy absorption advantage. A lot of research has been done in different cross sectional shapes and different tapered designs, with design for manufacturability in mind, to achieve high specific energy absorption. </div><div><br></div><div>In this study a novel type of tubular structure is proposed, in which predesigned origami initiators are introduced into conventional square tubes. The crease pattern is designed to achieve extensional collapse mode which results in decreasing the initial buckling forces and at the same time acts as a fold initiator, helping to achieve a extensional collapse mode. The influence of various design parameters of the origami pattern on the mechanical properties (crushing force and deceleration) are extensively investigated using finite element modelling. Thus, showing a predictable and stable collapse behavior. This pattern can be stamped out of a thin sheet of material. </div><div><br></div><div>The results showed that a properly designed origami pattern can consistently trigger a extensional collapse mode which can significantly lower the peak values of crushing forces and deceleration without compromising on the mean values. Also, a comparison has been made with the behavior of proposed origami pattern for extensional mode verses origami pattern with diamond fold.</div>

Roadside safety hardware has traditionally been approved on the basis of full-scale crash tests. In recent years, nonlinear dynamic Finite Element (FE) programs like LS-DYNA, PAM-Crash or ABAQUS Explicit have been widely used in evaluating new or improved design of roadside hardware. Although a powerful tool, numerical models must be properly verified and validated in order to provide reliable results. Typically, the verification and validation (V&V) process involves a visual comparison of two curves and is based on a purely subjective judgment. This research investigated the use of comparison metrics, which are mathematical measures that quantify the level of agreement between two curves, for comparing simulation and experimental outcomes in an objective manner. A computer program was developed in Matlab® to automatically evaluate most of the comparison metrics available in literature. The software can be used to preprocess and compare either single or multiple channels, guiding the user through friendly graphical interfaces. Acceptance criteria suitable to represent the typical scatter of experimental tests in roadside safety were determined by comparing ten essentially identical full-scale vehicle crash tests. The robustness and reliability of the implemented method were tested by comparing the qualitative score of the computed metrics for a set of velocity waveforms with the corresponding subjective judgment of experts. Moreover, the implemented method was applied to two real validation cases involving a numerical model in roadside safety and a model in biomechanics respectively. Eventually, the program showed to be an effective tool to be used for assessing the similarities and differences between two curves and, hence, for assisting engineers and analysts in performing verification and validation activities objectively.

acase@tulane.edu

The aim of this thesis was to examine the extent, and correlates, of self-regulation of driving behaviour among a sample of South Australian older drivers (aged 60 or more). The first of four studies was an analysis of official crash statistics in South Australia over a period of five years. The patterns of crash involvement for South Australian older drivers were found to resemble those reported in the literature for other jurisdictions. Lower levels of crash involvement for older drivers in difficult driving situations (peak hour, rain, darkness) were interpreted as indirect evidence for self-regulation of driving behaviour. The second study involved pilot testing a measure developed specifically for assessing the visual attention of older adults (the Computerised Visual Attention Test - CVAT). The CVAT assesses visual attention by measuring target detection and reaction time for central and peripheral stimuli, and in conditions requiring selective and divided attention. The third study involved assessing the test-retest reliability, construct validity and predictive validity of the CVAT. It was concluded that the CVAT is a reliable measure of abilities including, but not restricted to, attention, and that it is correlated with on-road driving ability. The fourth study involved an examination of the driving behaviour and attitudes of 104 drivers aged over 60, with avoidance of difficult driving situations providing an index of self-regulation. These drivers also completed a battery of tests measuring psychological factors, vision, physical functioning, various cognitive abilities, and attention (the CVAT). Ninety participants additionally completed an on-road assessment of driving ability. It was found that older drivers most often avoided reverse parallel parking and driving at night in the rain, while driving alone was avoided least often. Measures of visual attention, medication use and visual acuity were most predictive of levels of self-regulation, while poorer driving ability was only associated with avoidance of a small number of specific situations. Functional deficits related to poorer driving ability but not to self-regulation included poorer contrast sensitivity, speed of information processing and spatial memory. Such deficits could identify drivers who may need to restrict their driving more than they do. / Thesis (Ph.D.)--Department of Psychology, 2004.

Dans le cadre de l'étude par éléments finis du crash des structures aéronautiques, la prédiction des modes de ruine engendrés au sein ou au voisinage des assemblages rivetés, telle la déchirure d'une tôle le long d'une ligne de rivets, s'avère, encore aujourd'hui, délicate. Dans ce contexte, une méthodologie permettant la formalisation et la caractérisation d'un modèle de fragilisation structurale est proposée. Ce modèle a pour objectif de simuler la rupture d'une plaque métallique perforée à un niveau macroscopique. La notion de fragilisation structurale est rappelée dans la première partie du mémoire. Engendrée par présence de perforations, celle-ci a une incidence directe sur la tenue mécanique des structures et elle est définie comme la distribution inhomogène des déformations le long du futur chemin de rupture. Le rapport de la déformation locale, observée le long de ce chemin, à une déformation de référence permet d'accéder à une "mesure" particulière de cette fragilisation. Sur la base d'observations expérimentales menées en quasi-statique sur des éprouvettes perforées ou non, le second chapitre tente de proposer un cadre théorique qui permet de mieux comprendre les fondements physiques de l'exercice de modélisation proposé. Le formalisme algébrique de Dvorak est ensuite mis en œuvre dans le troisième chapitre, pour poser les premiers jalons d'une méthode numérique multi-échelle de caractérisation du modèle de fragilisation structurale. Le développement de ce modèle, entrepris dans un premier temps dans le domaine élastique, a permis de démontrer la faisabilité d'une telle approche. Le développement de cette démarche en plasticité est ensuite tenté et discuté. Le quatrième chapitre cherche enfin à étudier l'influence de la dynamique sur le modèle de fragilisation structurale, via une étude expérimentale mettant en œuvre des matériaux sensibles ou non à la vitesse de déformation.

In this paper, we discuss the consensus problem for synchronous distributed systems with orderly crash failures. For a synchronous distributed system of n processes with up to t crash failures and f failures actually occur, first, we present a bivalency argument proof to solve the open problem of proving the lower bound, min (t + 1, f + 2) rounds, for early-stopping synchronous consensus with orderly crash failures, where t < n - 1. Then, we extend the system model with orderly crash failures to a new model in which a process is allowed to send multiple messages to the same destination process in a round and the failing processes still respect the order specified by the protocol in sending messages. For this new model, we present a uniform consensus protocol, in which all non-faulty processes always decide and stop immediately by the end of f + 1 rounds. We prove that the lower bound of early stopping protocols for both consensus and uniform consensus are f + 1 rounds under the new model, and our proposed protocol is optimal. / Singapore-MIT Alliance (SMA)

Mass transportation systems, specifically bus systems, are a key element of the national transportation network. Buses are one of the safest forms of transportation; nonetheless, bus crashes resulting in occupant injuries and fatalities do occur. According to Traffic Safety Facts reports from 1999 to 2003, an average of 40 fatalities and 18,430 injuries of bus occupants have occurred per year, with side impact accounting for 14 % according to type of impact and by initial point of impact it accounts for 36%. A full scale crash test is considered the most reliable source of information regarding structural integrity and safety of motor vehicles. However, the high cost of such tests and difficulties in collecting data has resulted in an increasing interest in the analytical and computational methods of evaluation. With the advancement in computer simulations, full finite element validated vehicle models are being analyzed for different impact scenarios to predict vehicle behavior and occupant response. This thesis research work presents the procedure for development of a finite element (FE) model of a mass transit bus and the results of its crashworthiness and structural integrity analysis. The finite element model is developed by extracting mid-surface from solid cad model. This model is a detailed model with all parts. All parts are connected using different multi point constraints and special links with failure to model actual types of structural connections such as bolts and spot welds. LS-DYNA non-linear, explicit, 3-D, dynamic FE computer code was used to simulate behavior of the transit bus under different side impact scenarios. A parametric study is done to study structural response of transit bus when impacted by vehicles of different masses, sizes and shapes. A multibody analysis is done to study occupant response to different side impact crash conditions. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering / "December 2006."

Millions of square feet of mechanically stabilized earth retaining wall are constructed annually in the United States. When used in highway fill applications in conjunction with bridges, these MSE walls are typically constructed with a roadside barrier system supported on the edge of the wall. This barrier system generally consists of a traffic barrier or bridge rail placed on a continuous footing or structural slab. The footing is intended to reduce the influence of barrier impact loads on the retaining wall system by distributing the load over a wide area and to provide stability for the barrier against sliding or overturning. The proper design of the roadside barrier, the structural slab, and the MSE wall system requires a good understanding of relevant failure modes, how barrier impact loads are transferred into the wall system, and the magnitude and distribution of these loads. In this study, a procedure is developed that provides guidance for designing: 1. the barrier-moment slab, 2. the wall reinforcement, and 3. the wall panels. These design guidelines are developed in terms of AASHTO LRFD procedures. The research approach consisted of engineering analyses, finite element analyses, static load tests, full-scale dynamic impact tests, and a full-scale vehicle crash test. It was concluded that a 44.5 kN (10 kips) equivalent static load is appropriate for the stability design of the barrier-moment slab system. This will result in much more economical design than systems developed using the 240 kN (54 kips) load that some user agencies are using. Design loads for the wall reinforcement and wall panels are also presented.

Numerous studies have documented the application of crash severity models to explore the relationship between crash severity and its contributing factors. These studies have shown that a large amount of work was conducted on this topic and usually focused on different types of models. However, only a limited amount of research has compared the performance of different crash severity models. Additionally, three major issues related to the modeling process for crash severity analysis have not been sufficiently explored: sample size, model misspecification and underreporting in crash data. Therefore, in this research, three commonly used traffic crash severity models: multinomial logit model (MNL), ordered probit model (OP) and mixed logit model (ML) were studied in terms of the effects of sample size, model misspecification and underreporting in crash data, via a Monte-Carlo approach using simulated and observed crash data. The results of sample size effects on the three models are consistent with prior expectations in that small sample sizes significantly affect the development of crash severity models, no matter which model type is used. Furthermore, among the three models, the ML model was found to require the largest sample size, while the OP model required the lowest sample size. The sample size requirement for the MNL model is intermediate to the other two models. In addition, when the sample size is sufficient, the results of model misspecification analysis lead to the following suggestions: in order to decrease the bias and variability of estimated parameters, logit models should be selected over probit models. Meanwhile, it was suggested to select more general and flexible model such as those allowing randomness in the parameters, i.e., the ML model. Another important finding was that the analysis of the underreported data for the three models showed that none of the three models was immune to this underreporting issue. In order to minimize the bias and reduce the variability of the model, fatal crashes should be set as the baseline severity for the MNL and ML models while, for the OP models, the rank for the crash severity should be set from fatal to property-damage-only (PDO) in a descending order. Furthermore, when the full or partial information about the unreported rates for each severity level is known, treating crash data as outcome-based samples in model estimation, via the Weighted Exogenous Sample Maximum Likelihood Estimator (WESMLE), dramatically improve the estimation for all three models compared to the result produced from the Maximum Likelihood estimator (MLE).

Safety-shaped median barriers have long been employed to keep misguided vehicles on the roadway. In recent years there has been a growing national desire for more aesthetically pleasing roadside safety systems. Adding surface texture is one of the most popular ways to make a more aesthetically pleasing barrier. This practice of adding surface texture can potentially reduce the safety performance of the barrier. The purpose of this research was to develop guidelines for the aesthetic surface treatment of safety-shaped median barriers. Numerical simulation was utilized to develop these guidelines. This was done by first validating the vehicle model that was used in this research, which was the National Crash Analysis Center (NCAC) 2000P Detailed Pickup Truck model. The validity of the vehicle model could be determined by comparing the vehicle dynamics of the simulation to the actual crash test data for the smooth surfaced Single Slope and New Jersey Safety-Shaped barriers. Crash tests involving concrete median barriers most commonly fail crash testing criteria given by the National Cooperative Highway Research Program (NCHRP) Report 350 by excessive Occupant Compartment Deformation (OCD). OCD is excessive deformation of the occupant compartment that would cause severe harm to the occupant. Current simulation vehicle models do not give reliable direct measurement of OCD. To take the place of direct measurement, several parameters were measured to find the best surrogate measure of OCD. The internal energy of the floorboard in the NCAC 2000P Detailed Pickup Truck model gave the best correlation to OCD. By simulating several different past crash tests with passing and failing OCD, limits of internal energy in the floorboard could determine if a simulation had passing, marginal, or failing amounts of OCD. Using the surrogate measure of OCD a parametric study was then evaluated by NCHRP Report 350 standards. The parametric study of 29 simulations varied width and depth of recess between asperities for two different angles of asperities. Guidelines were determined for the 45? and 90? angles of asperities as a curve on depth vs. width of recess between asperities from the results of this parametric study.