Yi Yang Tay

A finite element analysis of high-energy absorption cellular materials in enhancing passive safety of road vehicles in side-impact accidents

In an effort to increase road vehicles’ structural strength, cellular materials, such as foam, have been utilised and installed in vital parts of the vehicle. The limited structural crush zones in side-impact collisions, when compared to frontal impacts, have shown to cause higher deformation to the passenger compartments that will lead to severe injury to the vehicle occupants. Therefore, the need to further enhance road vehicles’ passive safety system to protect the occupants during side-impact collisions is necessary. In addition to many passive safety features, cellular materials have been installed in current vehicles to serve as structural reinforcement by absorbing impact energy from transferring to the occupants. This study is aimed at investigating the effect of various cellular materials in enhancing vehicle crashworthiness such as side doors intrusion, interior doors acceleration and the internal energy of the cellular materials. To fulfil the objective of this paper, an existing finite element model of a sedan vehicle is modified to include a cellular material sandwiched in between the door panels. The cellular materials used for this study are IMPAXX, polyurethane foam, micro-agglomerated cork, DAX and CONFOR foams.The mechanical properties of the cellular materials utilised in the computational model are validated. Various dynamic responses of the vehicle structure with the inclusion of the five selected materials are numerically tested and compared against the vehicle structure without the cellular materials. Side-impact simulations in accordance to federal motor vehicle safety standard (FMVSS) No. 214 standard are used to replicate side-impact collisions. This study quantifies the energy absorption and side-door intrusion with different cellular padding. It also shows that the inclusion of cellular materials significantly reduces occupant compartments intrusion and deceleration of the vehicle by at least 30%. Therefore, the inclusion of cellular materials has shown promising results in improving the crashworthiness of road vehicles.

Crash simulations of aircraft fuselage section in water impact and comparison with solid surface impact

Aircraft water landing emergency provisions 14 CFR 25.801 demand requirement of ditching provision if requested in certification. This requires evaluation of the dynamic behaviour and response of aircraft in water impact to analyse the immediate injury to occupants. A correlated finite element model of a narrow-body Boeing-737 fuselage section and smoothed-particle hydrodynamics model of a body of water are coupled and utilised to investigate the structural response of the aircraft fuselage section when subjected to vertical drop test. The vertical drop of the fuselage section onto a body of water is simulated at an impact speed of 9.14 m/s, and also at higher impact speeds of 10.67 and 12.19 m/s. The vertical drop simulations are modelled using the non-linear explicit code, LS-DYNA, to predict the deformation of the fuselage section and acceleration pulses of the cabin floor, as well as the energy absorbed by the fuselage structure. The acceleration pulses from the cabin floor are then utilised as input for the occupant simulation performed using the mathematical code, MADYMO 7.5. The occupant model consists of a MADYMO FAA Hybrid-III 50th percentile dummy, a 2-point lap belt and a rigid seat. The lumbar loads experienced by the occupants in relation to both types of impacts are also presented. The dynamic simulation results from this study suggest that the fuselage section in water impact may be less severe than solid surface impact.

Multi-objective optimization of mechanisms with clearances in revolute joints

Despite extensive work on the evaluation of the dynamic performances of various mechanisms and multi-body mechanical systems with revolute joint clearances, limited work has been conducted in optimizing the performances of these systems. A multi-objective optimization technique is presented to examine and to quantify the effect of combined objective functions with several design variables on the response of the systems. In particular, a Kriging meta-model based on the Design-of-Experiment method is utilized to optimize the systems’ performance. The reason for implementing this meta-model is to replace the computational intensive simulations with a more efficient mathematical model. In this study, a simple slider-crank mechanism with a revolute clearance joint at the slider pin is modeled, and its dynamic response is analyzed using the multi-body dynamic software, MSC ADAMS. The revolute joint clearance is modeled as a pin-in-hole dry contact utilizing the Hertzian contact force model with hysteresis damping. Response surfaces are generated on the prediction of the system’s performances for three different objective functions and for different range of design variables. The objective functions are combined to develop a single response surface characterizing the dynamic responses of the system at different range of design variables in order to optimize its performance.

An experimental and numerical investigation into the dynamic crash testing of vehicle bumper fabricated using friction stir welding and gas metal arc welding

The advancement in friction stir welding (FSW) technology has provided automotive and aerospace industry with an alternative method in developing structures and assemblies. This study investigates the performance of FSW and gas metal arc welding (GMAW) on road vehicle bumpers. The method of investigation is to weld the bumper to the crash-box, and the assembly is mounted onto a moving deformable barrier before a dynamic crash test is performed. The bumper and crash-box is fabricated from AA6082-T6 and AA6063-T6 extrusions, respectively. In the first part of the study, the full-frontal crash testing of the FSW and GMAW fabricated bumper using experimental method is presented. The FSW and GMAW fabricated bumpers are subjected to 7, 10, 15 and 20 km/hr impact velocities against a rigid wall. The methods used to quantify the results are the post-crash deformation and stress distribution of the bumper as well as crack propagation at the weld joint. The non-linear dynamic software, LS-DYNA, is used exclusively in the second part of this study to replicate the experimental procedures using numerical methods. Finally, a 40% frontal offset test is conducted to evaluate the performance of the bumper when subjected to a different impact condition. It was shown that the FSW fabricated bumper can enhance the structural integrity and performance of the bumper at all impact velocities and configurations.

Multibody modelling of an internal gyroscopic micro-mechanism for development of lateral deviation of a projectile

The lateral control of a projectile for targeting and impacting a nonstationary target is of interest in many applications. Through the use of internal moving parts, gyroscopic forces can be generated, thus changing the flight trajectory of the projectile. In this study, three small internal swing masses are introduced to the projectile and their motions are controlled. The masses are attached to the end of massless rods that are located on points of an equilateral triangle centered about the major axis of the projectile. A mathematical model for the internal gyroscopic rotating disks of this multibody mechanism and its trajectory path is presented. For this mechanism, the dynamics equations of motion are developed and solved numerically to simulate the trajectory of the projectile. The concept projectile model is shown to move cyclically about the axis of rotation and to deviate from its axis in a relatively even slope. A parametric study is then focused on actuating each mass in sequence or changing the weight of the masses and their initial positions to examine and evaluate the flight trajectory of the projectile. The results from this study show that the lateral deviation of a projectile can be controlled by altering the initial configuration of the rotating mass mechanism. This application may hold merit for controlling the re-entry flight trajectory of air vehicles.

An Internal Gyroscopic Micro-Mechanism for Development of Lateral Deviation of a Projectile

The lateral control of a projectile for impacting a non-stationary target is of interest in many applications. Changing the flight trajectory can be achieved using the internal moving parts of the projectile. In this study, three small internal swing masses introduced to the projectile are controlled, and the masses are attached at the end of a massless rod. A mathematical model for the internal gyroscopic rotating disks of this mechanism and its trajectory path is developed. For this mechanism, the equations of motion are developed and solved numerically to simulate the trajectory of the projectile. The projectile is shown to move cyclically about the axis of rotation and deviate from its axis in a relatively even slope. A parametric study is conducted on actuating each mass in sequence or changing the weight of the mass to examine and evaluate the flight trajectory of the projectile. The results from this study show that the projectile could move in a lateral direction in a controlled manner by altering the mass mechanism in a predefined manner. This application may hold merit for controlling the re-entry flight trajectory of air vehicles.

Development and application of planar computational general-purpose constrained multibody simulations in Matlab with simple graphical/visualization capability

This study demonstrates the implementation and advantages in utilizing the Matlab programming environment for general-purpose simulations of constrained planar dynamic and kinematic multibody mechanical systems. Many currently available tools have a focus and can have limited flexibility through difficulty in data entry, limited access to source code, analysis of data or use of programming languages not readily taught. A Matlab source code is created, which includes the use of Microsoft Excel and GUI’s created in GUIDE that allow a user to construct, simulate and analyze multibody systems in Matlab. This technique allows the user to utilize any of Matlab toolboxes for unique problems or integrate the base program into a Simulink environment. An overview of the general code structure and multibody kinematics and dynamics equations used are shown in this paper. For kinematic simulations, the system’s Cartesian coordinates are found by finding the roots of the constraints vector at each time step. For the dynamic systems, the solver uses a numerical integration scheme with augmented form of the constrained equations of motion to solve for the system’s accelerations. Examples are presented demonstrating the benefits of using the Matlab environment and the flexibility to easily expand the code to simulate unique problems. These examples include an Ackermann steering for automotive applications and a double pendulum at the influence of gravity. The last example shows how a custom function can be created to inject forces into the dynamic solver in order to simulate a structural beam at the influence of a heavy pendulum.Copyright

Lumbar load estimation for a MADYMO FAA Hybrid-III scalable dummy

The Federal Aviation Administration (FAA) has a number of regulations aimed at protecting occupants in the event of a crash. The Code of Federal Regulations, 14 CFR 25.562, describes the compliance regulation for transport category aircraft, with similar regulations for other types of aircraft in Parts 23, 27 and 29. One of the required tests is the dynamic impact with a Hybrid-II or a FAA Hybrid-III 50th percentile dummy seated on a 60-degree pitched seat, with an input deceleration/acceleration pulse acting primarily on the mid-sagittal plane of the dummy. In particular, an important compliance criterion is that the lumbar/pelvic load must be below the 1,500 lb (6,672 N) compliance limit. The objective of this study is to develop a reasonable approach to estimate the lumbar load tolerance for potential future expansion of lumbar load regulations for other dummy sizes such as an FAA Hybrid-III 5th and 95th percentile dummy. To accomplish this, the lumbar load measured with the Hybrid-II and the FAA Hybrid-III 50th percentile dummy when subjected to the 19 g rigid seat impact tests and simulations are correlated and discussed. The FAA Hybrid-III 50th percentile dummy is then scaled to the 5th and 95th percentile sizes based on GEBOD database. The dynamic behavior of the scaled FAA dummies in the 19 g sled simulation using an ideal acceleration pulse is then simulated and their corresponding lumbar loads are estimated. The dummy models utilized are obtained from the MADYMO crash test dummy database and the dynamic impact simulations are solved using the non-linear multibody dynamic solver, MADYMO. This study proposes the lumbar load tolerances for the 5th and 95th percentile sizes represented by the scaled FAA dummies by correlating their lumbar loads to the Dynamic Response Index (DRI) values. In this study, the lumbar load tolerance values for the 5th and 95th percentiles are proposed to be 870.4 lb (3,871.7 N) and 1772.9 lb (7,886.3 N), respectively. A comparison of the lumbar load tolerances proposed from this study and other sources is also presented.Copyright

Finite element analysis, Ground Vibration Testing, and characterization of vibration modes for a cantilever plate representing an aircraft wing with and without secondary structure attached

One of the most critical testing procedures for an airplane certification is Ground Vibration Testing (GVT). With proper GVT analysts can determine the stiffness distribution, natural frequencies, mode shapes and structural damping of each airplane components, which are needed for flutter and dynamic loads analyses. Hence, the results from GVT are crucial. The problem identified in this study is focused on structural design, which can lead to catastrophic situations, if proper attention is not given to GVT results. In GVT, analysts attempt to instrument most of the primary components of the airplane while often neglecting secondary structures such as bungees, gears, control surfaces, etc. These secondary structures must also be considered during GVT in identifying the in-phase and out-of-phase modes in order to achieve higher accuracy when tuning the stiffness of the primary structure. During the stiffness tuning process for the flutter analysis, tuning the primary structure stiffness to in-phase torsion mode can be considered as a conservative approach and will require design change. Conversely, if the stiffness of the primary structure is tuned to out-of-phase torsion mode, which is always higher, the analysis becomes unconservative. The goal of this study is to reconstruct the above-mentioned problem of in-phase and out-of-phase vibration modes of a cantilever plate with an attached secondary structure, replicating a simple model of aircraft wing structure. This includes performing the modal experiments and finite element analysis (FEA) of a cantilever plate (primary structure) with and without flexible links (secondary structure) attached to the plate and characterizing the in-phase and out-of-phase modes of the flexible links. A thorough study using frequency response functions (FRFs) is performed to characterize the modes using different accelerometer ‘raw data’ readings measured from different locations on the dynamic system. For GVT of the cantilever plate, natural frequencies associated with the respective mode shapes are identified and calculated and a comparison is made between the test results, the FEA results, and from an analytical approach. A parametric study is then conducted to evaluate and quantify the change in the frequencies of the in-phase and out-of-phase modes with the change in the chord-wise and span-wise location of the flexible attachment of the secondary structure to the primary structure, and due to the change in the compliant stiffness of the flexible link to the plate. Proper identification and correlation of the modes and natural frequencies of the cantilever plate with and without the secondary structure are presented. It is concluded that the in-phase and out-of-phase torsion frequencies increased with higher compliant stiffness. With the chord-wise change in location of the flexible link, both the in-phase and out-of-phase frequencies increased when the center of gravity of the link move towards the center of the chord from both leading and trailing edges of the plate. With the span-wise change in CG of the link, the in-phase frequency reduced with span (i.e., when the CG moves away from the constraint location of the plate) and the out-of-phase frequency increased.Copyright

Energy Absorption Characteristics of a Thin-Walled Tube Filled With Carbon Nano Polyurethane Foam and Application in Car Bumper

Over the past few decades, much research work has been conducted on the development of advance crashworthy structures to increase the energy absorption of mechanical systems. Thin-walled tubes are primarily used as structural reinforcements and as energy absorbing components. The high-energy absorption characteristics of cellular foams have attracted great attention to further enhance this superior capability. In particular, nanotechnology has been utilized in the development of advanced cellular materials for the automotive and aerospace industry. The primary objective of this study is to conduct a parametric study using experimental and finite element methods to examine and quantify the performances of thin-walled tube when filled with carbon nano particulates. To accomplish this study, compression tests are carried out to obtain the load-deflection curves of the nano-foams when subjected to different weight percentages of carbon nano fibers. Next, the specific energy absorbed and the collapse mechanism of nano foam filled thin-walled tubes are analyzed and compared with the empty ones. Finally, an illustrative study on the use of nano foams for vehicular applications is presented by using a vehicle bumper numerical model. The carbon nano foam is installed into the cavity of the bumper model and a full-frontal crash simulation is performed. Overall, this study has shown that the energy absorption capacity of thin-walled structures can be significantly enhanced with the use of carbon nano foams.Copyright