Residual Crush Research Articles

Crushing of Single-Walled Corrugated Board during Converting: Experimental and Numerical Study

Corrugated cardboard is an ecological material, mainly because, in addition to virgin cellulose fibers also the fibers recovered during recycling process are used in its production. However, the use of recycled fibers causes slight deterioration of the mechanical properties of the corrugated board. In addition, converting processes such as printing, die-cutting, lamination, etc. cause micro-damage in the corrugated cardboard layers. In this work, the focus is precisely on the crushing of corrugated cardboard. A series of laboratory experiments were conducted, in which the different types of single-walled corrugated cardboards were pressed in a fully controlled manner to check the impact of the crush on the basic material parameters. The amount of crushing (with a precision of 10 micrometers) was controlled by a precise FEMat device, for crushing the corrugated board in the range from 10 to 70% of its original thickness. In this study, the influence of crushing on bending, twisting and shear stiffness as well as a residual thickness and edge crush resistance of corrugated board was investigated. Then, a procedure based on a numerical homogenization, taking into account a partial delamination in the corrugated layers to determine the degraded material stiffness was proposed. Finally, using the empirical-numerical method, a simplified calculation model of corrugated cardboard was derived, which satisfactorily reflects the experimental results.

Post-accident evidence basis for new equestrian standards: Relationship between helmet liner residual crush and accident parameters

An in-depth analysis of 216 equestrian helmets involved in real-world accidents, with accompanying laboratory drop-test experiments has focussed on the crushing of energy absorbing liners. The mean measured residual crush (i.e., damage in the form of permanent deformation of helmet liner expressed as a percentage of the local undeformed thickness) was 21.5%. For front, rear and side impacts that occurred against both rigid and soft surfaces, the amount of residual crush varied linearly with impact velocity, peak translational acceleration, and maximum dynamic crush. For all impact locations, the percentage of energy absorbed by the helmet during an impact with a rigid surface is significantly less (between 4% and 20%) than those of both un-helmeted and helmeted headform soft surface impacts. Thus, the amount of helmet residual crush provides important insight into real-world equestrian accidents. This approach provides an evidence basis to improve future certification standards. There is clear scope to improve helmet designs, as helmet performance is clearly not optimised either for impact against soft surfaces or for relatively low velocity impacts. We suggest a peak impact power threshold that would improve equestrian helmet energy absorption for soft surface impacts without altering current standard test methodologies.

Repeated Impacts Diminish the Impact Performance of Equestrian Helmets.

Context: During thoroughbred races, jockeys are placed in potentially injurious situations, often with inadequate safety equipment. Jockeys frequently sustain head injuries; therefore, it is important that they wear appropriately certified helmets. Objective: The goals of this study are (1)to perform impact attenuation testing according to ASTM F1163-15 on a sample of equestrian helmets commonly used by jockeys in the United States and (2)to quantify headform acceleration and residual crush after repeat impacts at the same location. Participants and Design: Seven helmet models underwent impact attenuation testing according to ASTM F1163-15. A second sample of each helmet model underwent repeat impacts at the crown location for a total of 4 impacts. Setting: Laboratory. Intervention: Each helmet was impacted against a flat and equestrian hazard anvil. Main Outcome Measures: Headform acceleration was recorded during all impact and computed tomography scans were performed preimpact and after impacts 1 and 4 on the crown to quantify liner thickness. Results: Four helmets had 1 impact that exceeded the limit of 300g. During the repeated crown impacts, acceleration remained below 300g for the first and second impacts for all helmets, while only one helmet remained below 300g for all impacts. Foam liner thickness was reduced between 5% and 39% after the first crown impact and between 33% and 70% after the fourth crown impact. Conclusions: All riders should wear a certified helmet and replace it after sustaining a head impact. Following an impact, expanded polystyrene liners compress, and their ability to attenuate head acceleration during subsequent impacts to the same location is reduced. Replacing an impacted helmet may reduce a rider's head injury risk.

The effect of motorcycle helmet fit on estimating head impact kinematics from residual liner crush

Proper helmet fit is important for optimizing head protection during an impact, yet many motorcyclists wear helmets that do not properly fit their heads. The goals of this study are i) to quantify how a mismatch in headform size and motorcycle helmet size affects headform peak acceleration and head injury criteria (HIC), and ii) to determine if peak acceleration, HIC, and impact speed can be estimated from the foam liner’s maximum residual crush depth or residual crush volume. Shorty-style helmets (4 sizes of a single model) were tested on instrumented headforms (4 sizes) during linear impacts between 2.0 and 10.5m/s to the forehead region. Helmets were CT scanned to quantify residual crush depth and volume. Separate linear regression models were used to quantify how the response variables (peak acceleration (g), HIC, and impact speed (m/s)) were related to the predictor variables (maximum crush depth (mm), crush volume (cm3), and the difference in circumference between the helmet and headform (cm)). Overall, we found that increasingly oversized helmets reduced peak headform acceleration and HIC for a given impact speed for maximum residual crush depths less than 7.9mm and residual crush volume less than 40cm3. Below these levels of residual crush, we found that peak headform acceleration, HIC, and impact speed can be estimated from a helmet’s residual crush. Above these crush thresholds, large variations in headform kinematics are present, possibly related to densification of the foam liner during the impact.

Dynamic Response and Residual Helmet Liner Crush Using Cadaver Heads and Standard Headforms.

Biomechanical headforms are used for helmet certification testing and reconstructing helmeted head impacts; however, their biofidelity and direct applicability to human head and helmet responses remain unclear. Dynamic responses of cadaver heads and three headforms and residual foam liner deformations were compared during motorcycle helmet impacts. Instrumented, helmeted heads/headforms were dropped onto the forehead region against an instrumented flat anvil at 75, 150, and 195J. Helmets were CT scanned to quantify maximum liner crush depth and crush volume. General linear models were used to quantify the effect of head type and impact energy on linear acceleration, head injury criterion (HIC), force, maximum liner crush depth, and liner crush volume and regression models were used to quantify the relationship between acceleration and both maximum crush depth and crush volume. The cadaver heads generated larger peak accelerations than all three headforms, larger HICs than the International Organization for Standardization (ISO), larger forces than the Hybrid III and ISO, larger maximum crush depth than the ISO, and larger crush volumes than the DOT. These significant differences between the cadaver heads and headforms need to be accounted for when attempting to estimate an impact exposure using a helmet's residual crush depth or volume.

Vector model of vehicle collisions for inferring velocity from loss of kinetic energy with restitution on residual crush surface

In the standard mathematical model that underpins the inference of velocity change from vehicle damage in road accident reconstruction, the point where the colliding bodies engage is taken to lie in the same location as the point of application of the average impact force, usually in the central region of the crush zone or on the residual crush surface. Mathematical and physical reasons suggest the fidelity of the model could be deepened by allowing for a separation of these points, for example by locating the impulse or average force in the central region of the crush zone and defining engagement (common velocity or rebound) relative to the crush surface. Refinement of the theory revealed that the solutions for the change of linear and angular velocity are unaffected. For long-running in-depth research studies, this means that historical calculations of velocity change (delta-V) and related analyses on such topics as injury risk curves, countermeasure effectiveness and accident scenarios are not potentially undermined. Relative and absolute velocity are however affected. This was illustrated using crash test data where adjustments of 6 and 12 cm resulted in changes of up to 4% in road speed.

Simplified method for evaluating energy loss in vehicle collisions

A method is proposed for the evaluation of energy loss in road vehicle collisions. The energy loss evaluation is an essential task to reconstruct the dynamics of a road accident. The proposed method combines the simplicity of visual evaluation, typical of the method based on EES (equivalent energy speed), with flexibility, in order to evaluate the energy loss on any kind of vehicle deformation profile, of the methods based on measuring residual crush. The method is based on linearizing the damage profile, so that it is possible to predetermine the analytical expression of the kinetic energy loss in relation to only two parameters that characterise the shape of the damage. The stiffness of the vehicle is determined by estimating the geometric parameters of the damage starting from a photograph of generic damage, with documented EES, on a vehicle of the same model as the one under investigation. The proposed method was validated performing crash tests and using data from crash tests found in the literature. The method estimate with sufficient accuracy the kinetic energy loss in deformation on vehicles. The method, thanks to its simplicity and versatility, can constitute a valid alternative to the classic procedures for evaluating energy loss commonly utilised.

Energy loss in vehicle to vehicle oblique impact

Since the seventies, many methodologies have been developed for estimating from energy loss the delta V produced in a vehicle to vehicle impact. Normal energy loss, is calculated by a discrete number of residual crush measurements in the direction parallel to the vehicle's axis, using the stiffness coefficients. In the case of oblique impact, a correction factor is applied to the normal energy loss to determine energy loss in the impulse direction. In this paper the concept of principal direction of deformation is introduced, presenting a new method for estimating energy loss in vehicle to vehicle collision, starting from a discrete number of crush measurements, which are, however, performed considering the effective displacement of the points during the crush. This novel approach, in addition to providing a more rigorous model of the physical phenomena, leads to improvement in the results: with the new approach, the mean error committed in estimating energy loss is about 10%, as compared to the 20% of the previous methodology.

Empirical model for impact response of motorcycle front spoked wheel-tyre assembly

An experimental study on the response of the motorcycle front wheel-tyre assembly in a frontal impact was conducted. A topological approach was employed whereby the post-impact projected deformation area of the wheel was selected as the response variable. Design factors included in the design of experiment were impact speed (S), impact mass (M), inflation pressure level of the tyre (P), contact geometry of the striker (G), and the offset distance of the impact location from the axle (D). A 2v5-1 fractional factorial design with four replications was applied. Statistical software, Minitab version 13, was employed in the experimental design and data analysis. The impact tests were conducted using the in-house developed pendulum impact test rig. A factorial analysis was performed to identify the significant factors influencing the responses of the wheel-tyre assembly. It was found that the influential effects for the response, excluding the torn-off cases, are the main effects S, M, P, and D, and interaction effects SM and PG. On the other hand, for the response including the torn-off cases, the main effects are the same but the interaction effects are slightly different, namely SM, MD, MG, and PG. These factors were then incorporated in the establishment of the empirical models for predicting the impact response of the wheel-tyre assembly. Regression analysis was also carried out to evaluate the yielded empirical models. Curves demonstrating the behaviour of the wheel under various impact conditions investigated were generated based on the empirical models. A comparison was also made with the findings where maximum residual crush was the response variable.

An experimental study of deformation behaviour of motorcycle front wheel-tyre assembly under frontal impact loading

Experiments were conducted to study the deformation behaviour of front wheel-tyre assembly of a motorcycle when subjected to frontal impact loading. Impact tests were conducted using an in-house developed pendulum impact test apparatus. Statistical software, Minitab version 13, was employed to support the entire experimental process. Some of the parameters that influence response of the motorcycle in a frontal crash, viz., impact speed, impact mass, inflation pressure level of the tyre, contact geometry of the striker and offset distance of impact location from the axle were varied during the experiments. A 2 V 5 - 1 fractional factorial design was incorporated in the experimental investigation and is described in detail. Experimental results are presented in terms of the maximum residual crush sustained by the wheel, normalized area of deformation and dissipated impact energy. Regression analysis to relate the impact energy to maximum residual crush and normalized area of deformation was then performed. It was found that the deformation of the wheel-tyre assembly is well correlated to the dissipated impact energy. Factorial analysis was also performed to investigate the effect of individual parameters on response of the assembly. These are presented in factorial plots, followed by a brief discussion.

Structural adaptivity for acceleration level reduction in passenger car frontal collisions

A mathematical model was developed to explore and demonstrate the injury reducing potential of an adaptable frontal stiffness system for full frontal collisions. The model was validated by means of crash tests and was found to predict the peak accelerations of the crash test vehicles well, whereas correlation concerning mean acceleration or residual crush was not found. Vehicles were divided into three mass classes, and a test matrix was established in order to evaluate different combinations of vehicles involved in frontal crash at three closing velocities. In a baseline simulation setup, constant stiffness values were used and the results were compared to the corresponding simulations using adaptable frontal stiffness. Results show promising acceleration peak reductions at low speeds, implying that injury risk reductions are possible.

A Novel Approach to Vehicle Dynamics using the Theory of a Cosserat Point and its Application to Collision Analyses of Platooning Vehicles

A fully three-dimensional, computationally inexpensive vehicular model is presented. In contrast to traditional rigid body models, the vehicle's sprung mass is modeled as a (nonlinearly) deformable body. The formulation of the equations of motion is based on a continuum theory known as the theory of a Cosserat point. These equations largely preserve the relative simplicity of rigid body dynamics but incorporate deformable features. The ease of computer implementation permits the simultaneous simulation of vehicle and collision dynamics of multiple vehicles and highway objects. In this paper, the theory of a Cosserat point is summarized and its general application to vehicle and collision dynamics is illustrated. A three-dimensional collision algorithm is discussed with emphasis on small closing velocities (negligible residual crush, elastic rebound). The novel model is compared to standard procedures.