William Altenhof

Methods to mitigate injury to toddlers in near-side impact crashes

This research focuses on the injury potential of children seated in forward-facing child safety seats during side impact crashes in a near-side seated position. Side impact dynamic sled tests were conducted by NHTSA at Transportation Research Center Inc. (TRC) using a Hybrid III 3-year-old child dummy seated in a convertible forward/rearward child safety seat. The seat was equipped with a LATCH and a top tether and the dummy was positioned in forward-facing/near-side configuration. The test was completed using an acceleration pulse with a closing speed of 24.1 km/h, in the presence of a rigid wall and absence of a vehicle body. A fully deformable finite element model of a child restraint seat, for side impact crash investigations, has been developed which has also been previously validated for frontal and far side impacts. A numerical model utilizing a Hybrid III 3-year-old dummy, employing a similar set-up as the experimental sled test was generated and simulated using LS DYNA. The numerical model was validated by comparing the head and the chest accelerations, resultant upper and lower neck forces and moments from the experimental and numerical tests. The simulation results were observed to be in good agreement to the experimental observations. A numerical model of the near-side laboratory tests, utilizing a Q3s child dummy, was also created for parametric studies regarding different ISOFIX configurations. Further, numerical simulations were completed for both the dummy models with rectangular and cross-shaped sections of rigid ISOFIX systems. In addition, studies were conducted to confine lateral movement of the dummys head by adding energy absorbing foam on the side wings in the vicinity of the contact region of the CRS. It was observed that the use of rigid ISOFIX system reduced the lateral displacement of the CRS and different injury parameters. Addition of energy absorbing foam blocks was effective in further reducing the lateral displacement of the dummys head. The lateral displacement of the head was reduced by 68 mm by using cross-shaped section ISOFIX with energy absorbing foam near the vicinity of the head of the Hybrid III 3-year-old dummy compared to the flexible LATCH configuration without foam. For the Q3s dummy, the lateral displacement of the head was reduced by 48 mm by utilizing a cross-shaped section rigid ISOFIX system with the addition of energy absorbing foam compared to the flexible LATCH configuration.

Numerical simulation of AM50A magnesium alloy under large deformation

Abstract The present research concentrates on the development of a material model for the AM50A magnesium alloy, frequently used in the automotive industry. This computer model was developed and validated through experimental and numerical simulation of standardized charpy and tensile tests, and intensive microstructural analysis. The material model was further used to predict the behavior of an AM50A magnesium alloy steering wheel armature. Experimental and numerical impact tests were performed, correlated and validated by detailed structural analysis of the armature. Three material models were evaluated in the present research including a bilinear approximation, piecewise linear, and Johnson–Cook models. The piecewise linear model presented accurate predictive capabilities with variations explained by microstructural defects existing within the specimen being tested. In addition, a failure criterion was proposed and assessed during numerical simulations of the charpy impact tests.

Comparison of the load/displacement and energy absorption performance of round and square AA6061-T6 extrusions under a cutting deformation mode

Abstract Quasi-static compressive testing of extruded aluminum alloy AA6061-T6 round and square cross-sectional tubular specimens was completed to investigate the crush characteristics of these structural members under a cutting deformation mode by using a specially designed cutting tool. Results from the experimental tests showed that the cutting deformation mode of the round and square tubes exhibited high crush force efficiencies (CFE) of 0.95 and 0.81 respectively. In comparison, CFE of round specimens that experienced progressive folding and global bending deformation modes were observed to be 0.66 and 0.20 respectively and CFE of square specimens that underwent global bending were found to be 0.22. An almost constant cutting force was observed for the round tubes in the cutting deformation mode, while a slight increase in the cutting force was observed for the square tubes under the same deformation mode. The increase in cutting force for the square tubes was observed to occur primarily due to contact arising between the cutting tool and tube sidewalls and to a lesser extent due to bending of the petalled side walls. For the round tubes, contact between the cutting tool and sidewalls as well as bending of the petalled side walls was not as significant and resulted in a more consistent cutting force. For both the 200 mm and 300 mm length tubes the total energy absorption for the round and square tubes was observed to be 6.11 kJ and 4.31 kJ respectively. The energy absorption was observed to be independent of tube length.

Dynamic stress concentrations for an axially loaded strut at discontinuities due to an elliptical hole or double circular notches

Abstract Numerical modeling, simulation, and analysis of axial struts with geometrical discontinuities subjected to dynamic loading conditions is the focus of this paper. Understanding how geometrical discontinuities influence the stress distribution within a structural member is critical for design applications. Furthermore, understanding how axial struts perform under dynamic loading conditions is critical in the design of automobiles, airplanes, and a large number of potentially dynamically loaded structures. A large amount of research investigating static loading conditions of struts with geometrical discontinuities has been conducted. With the development of finite element (FE) codes, numerical dynamic analyses can be completed much easier and at much lower costs than would occur for experimental methods. In this research, FE simulations were conducted on struts with centrally located elliptical discontinuities. A good correlation was found between the results from these simulations and experiments conducted using the photolaserelastic technique. Based on these correlations, models of struts with circular notches located at the sides of the strut were simulated under the same loading condition. The stress distributions of the models were studied to determine the maximum stress state for each geometric configuration. This information was used to determine the dynamic stress concentration factor for each configuration. Three-dimensional surface plots were constructed illustrating how the numerically determined dynamic stress concentration factor varies with strut and discontinuity geometry. Design equations are presented that relate the dynamic stress concentration factor to non-dimensional geometric parameters. These equations are a useful tool for engineers involved in automotive and aerospace component design.

An investigation into the head and neck injury potential of three-year-old children in forward and rearward facing child safety seats

Abstract This research focuses on the injury potential of children in forward and rearward facing child restraint seats in frontal collisions. Experimental sled tests were completed following the guidelines outlined in the Federal Motor Vehicle Safety Standard 213 using a Hybrid III 3-year-old dummy in a convertible forward/rearward facing child restraint seat. The seat was equipped with a five point child safety belt and the experimental test was completed in the forward facing configuration. The Hybrid III 3-year-old dummy was equipped with three uniaxial accelerometers arranged in mutually perpendicular directions in the head and chest. A numerical model employing a subset of the apparatus used in the forward facing experimental sled test was developed and numerically simulated using LSDYNA. To verify the numerical simulations, the head and chest accelerations were compared to the experimental findings and it was observed that a reasonable correlation between the data existed. Further numerical simulations were completed to investigate the influence of positioning the 3-year-old dummy in the rearward configuration on the head and neck injury potential during frontal crash. Through an analysis of injury criteria, using neck loads and head accelerations, it was observed that the rearward facing child dummy sustained significantly lower levels of neck injury criteria while exhibiting similar levels of the head injury criteria as the forward facing child dummy.

Finite Element Modeling of the Axial Crushing of AA6061 T4 and T6 and AA6063 T5 Structural Square Tubes with Circular Discontinuities

This research focused on the energy absorption capabilities of axially loaded structures fabricated from aluminum alloy extruded tubing with a square cross section. Quasi-static compressive testing was used to examine the effects of dual centrally-located circular hole discontinuities on the energy absorption characteristics of the extrusion test specimens. In addition to previously characterized progressive buckling and global bending modes, collapse modes involving cracking and splitting were observed in several experimental tests. For this reason, finite element models of each test specimen were developed using a material model incorporating damage mechanics. The suitability of using shell elements versus solid elements to model these relatively thick walled structures was investigated. A good correlation was observed between the results of the experimental quasi-static compressive tests and the results of the finite element simulations conducted using LS-DYNA.

An experimental investigation into the energy absorption and force/displacement characteristics of aluminum foam filled braided stainless steel tubes under quasistatic tensile loading conditions

Abstract Experimental tensile testing of aluminum foam filled braided stainless steel tubes was completed in this research investigation. The kinematic constraints imposed on the individual tows of the braided tube provided for a reduction in tube diameter under axial elongation of the tube ends. Encasing an aluminum foam core within the tube and deforming the structure under tensile loading was completed to examine the load/displacement and energy/displacement relationships for this novel approach for energy absorption. In addition, the influence of aluminum foam density on the load bearing capacity and energy absorption characteristics was considered. Five different foam densities were investigated for the tube cores which varied between 249 kg/m3 to 373 kg/m3. In addition to the results from the aluminum foam filled braided stainless steel tube tensile tests, observations on the load/displacement characteristics of unfilled braided stainless steel tubes are presented as well as compressive engineering stress/strain characteristics for densities of aluminum foam considered in this research. Results from the experimental tests indicated that the 405 mm length foam filled braided tubes illustrated three distinct load bearing regions. The first region was associated with a somewhat constant load bearing capacity with energy absorption resulting from tensile fracture and compression of the foam core. The second region was associated with load stiffening characteristics where the foam underwent significant radial crushing. Finally the third region was associated with axial deformation of the braided tube. Energy absorption capacities, for the foam densities and tube lengths considered in this research, ranged from approximately 5.2 kJ to 7.9 kJ. The tensile force efficiency, which is similar to the crush force efficiency, in the first load bearing region was found to range from 0.46 to 0.55.

A numerical investigation into the effect of CRS misuse on the injury potential of children in frontal and side impact crashes

This research focuses on an investigation into the head and neck injuries sustained by toddlers due to CRS misuse under frontal and side impact crashes. A fully deformable FE model incorporating a Hybrid III 3-year-old dummy was developed which has been previously validated for frontal impacts under CMVSS 208 and FMVSS 213 testing conditions. Furthermore, this model has also been validated under near-side impact conditions in accordance to crash tests carried out by NHTSA. In addition, numerical models incorporating a Q3/Q3s prototype child crash test dummies were developed. The objective of this research was to study the effect of seatbelt slack and the absence of the top tether strap on the head and neck injuries sustained by toddlers in a vehicle crash. Numerical simulations were conducted under full frontal and near side impact crash testing conditions in accordance with FMVSS 213 for the Hybrid III 3-year-old dummy and Q3/Q3s dummies in the absence and presence of slack in the seatbelt webbing, and in the absence and presence of the top tether strap. In addition, the effect of using a cross-shaped rigid ISOFIX system was also investigated. An analysis of the head and chest accelerations, neck loads and moments was completed to investigate the potential of injury due to CRS misuse. An increase in HIC(15) by approximately 30-40% for the frontal impact and 10-20% for the near-side impact respectively was observed for the Q3 child dummy due to both forms of CRS misuse. In the absence of the top tether strap the forward head excursions were observed to be increased by approximately 70% for the Hybrid III 3-year-old dummy and 40% for the Q3 dummy, respectively. Use of the cross-shaped rigid ISOFIX system illustrated a reduction in head and neck injury parameters, for both frontal and side impact conditions, in the absence and presence of CRS misuse. CRS misuse results in a significant increase in injury parameters and potential for contact related head injuries. Use of a rigid ISOFIX system to restrain a CRS provides better CRS and dummy confinement and reduced injury potential than a flexible ISOFIX system.

Deformation behaviour of aluminium during machining: Modelling by Eulerian and smoothed-particle hydrodynamics methods

Large-strain deformation behaviour of aluminium that accompanies continuous chip formation during machining (1100 Al) has been studied using experimental and numerical techniques. In experimental studies, local values of plastic strains were determined in the primary and the secondary deformation zones of machined 1100 Al. This was completed through a careful examination of metallographic sections taken from the material ahead of the tool tip, in which orientation changes in the flow lines in the material and shear angles were used to calculate plastic strains. Variations in local flow stresses were estimated from microhardness measurements. The examination of the stresses and strains at each measurement location generated a stress—strain relationship for the 1100 Al material. An important observation from the experimental portion of this research indicated that the material stress—strain response was independent of the feed rates considered in this study. Additionally, the response was observed to obey an exponential relationship with stress saturation occurring at approximately 300 MPa. Parameters associated with the Johnson—Cook constitutive equation were also determined from the experimental work. An Eulerian finite-element method and a relatively new so-called mesh-free method [smoothed-particle hydrodynamics (SPH) method] have been applied to the simulation of machining. The application of these methods permits simulation of the machining process without use of any mesh separation criterion. Appropriate values of the coefficients of friction, for numerical studies, were determined in parametric studies by correlating the experimentally measured chip thicknesses with the numerically predicted values. The effectiveness of the Eulerian and SPH methods in predicting the response of 1100 Al during orthogonal machining has been assessed through a rigorous comparison of the stress—strain distribution within formed chips during steady-state cutting. Both the Eulerian and SPH models showed good overall correlation with the experimentally measured stress—strain distribution when the exponential type material behaviour was assumed in modelling. A maximum stress of 300 MPa at the tool tip was obtained from the numerical simulations using the assumed exponential material behaviour. The location of maximum stress corresponded to the position of maximum strain (8.0). The application of the Johnson—Cook type constitutive equation resulted in predicting a lower maximum equivalent strain (4.5) and higher maximum stresses (325 MPa).

Experimental observations of AA6061-T6 round extrusions under a cutting deformation mode with a deflector

A cutting deformation mode of AA6061-T6 round extrusions initiated by a heat-treated 4140 steel alloy cutter incorporating a deflector was investigated experimentally considering the load/displacement and energy absorption characteristics. Two different geometries of the cone-shaped deflectors, namely, straight and curved profiles, were considered in this research. The tubular specimens utilised in this experimental investigation were round AA6061-T6 tubes of lengths 200 mm with a nominal wall thickness of 3.175 mm and an external diameter of 50.8 mm. In addition to these specimens, additional extrusions were tested such that a progressive folding and global bending deformation mode was observed. Specimens which experienced global bending were of identical cross-sectional geometry as the extrusions which experienced cutting; however, the lengths of these extrusions were 300 mm. Results from the experimental tests showed that the cutter penetrated through the extrusion and formed petalled sidewalls which contacted the deflector and initiated bending in the petalled sidewalls. An almost constant cutting force, of magnitude 45 kN, was observed for the cutting deformation mode without the deflector. The presence of the straight or curved deflectors generated fluctuations in the cutting force which were significantly less than the variations in load for the specimens which experienced progressive folding, resulting in an increase in the crush force efficiency. As a result of the bending imposed on the petalled sidewalls from the deflector, a reduction in the steady state cutting force, to approximately 37 kN, was observed.