Duane S. Cronin

C4–C5 segment finite element model development, validation, and load-sharing investigation

Detailed cervical spine models are necessary to better understand cervical spine response to loading, improve our understanding of injury mechanisms, and specifically for predicting occupant response and injury in auto crash scenarios. The focus of this study was to develop a C4-C5 finite element model with accurate representations of each tissue within the segment. This model incorporates more than double the number of elements of existing models, required for accurate prediction of response. The most advanced material data available were then incorporated using appropriate nonlinear constitutive models to provide accurate predictions of response at physiological levels of loading. This tissue-scale segment model was validated against a wide variety of experimental data including different modes of loading (axial rotation, flexion, extension, lateral bending, and translation), and different load levels. In general, the predicted response of the model was within the single standard deviation response corridors for both low and high load levels. Importantly, this model demonstrates that appropriate refinement of the finite element mesh, representation at the tissue level, and sufficiently detailed material properties and constitutive models provide excellent response predictions without calibration of the model to experimental data. Load sharing between the disc, ligaments, and facet joints was investigated for various modes of loading, and the dominant load-bearing structure was found to correlate with typical anatomical injury sites for these modes of loading. The C4-C5 model forms the basis for the development of a full cervical spine model. Future studies will focus on tissue-level injury prediction and dynamic response.

Cervical spine segment finite element model for traumatic injury prediction.

Many detailed cervical spine models have been developed and primarily used to investigate kinematic response of the neck in impact scenarios. However, the goal of detailed models is to predict both kinematic response and provide insights into injury mechanisms and thresholds through tissue-level response. The objective of this study was to verify and validate an enhanced cervical spine segment finite element model to predict tissue-level failure under four load conditions: tension, flexion, and extension using a C4-C5 segment, and compression using a C5-C6-C7 segment. Mechanical tissue test data in relevant modes of loading was used in the model, and this data was also used to model ultimate tissue failure. The predicted failure locations were representative of reported cervical spine injuries for the different modes of loading, and the predicted peak failure forces were within the reported experimental corridors. The displacement to failure of the tension simulation was lower than expected in some cases, attributed to limitations in the constitutive model. This study provided a validated approach to predict tissue-level failure for cervical spine segments, predicting the location and sequence of tissue failure, and can be applied to future full cervical spine models for the prediction of injurious loading in automotive crash scenarios.

Cervical spine response in frontal crash

Predicting neck response and injury resulting from motor vehicle accidents is essential to improving occupant protection. A detailed human cervical spine finite element model has been developed, with material properties and geometry determined a priori of any validation, for the evaluation of global kinematics and tissue-level response. Model validation was based on flexion/extension response at the segment level, tension response of the whole ligamentous cervical spine, head kinematic response from volunteer frontal impacts, and soft tissue response from cadaveric whole cervical spine frontal impacts. The validation responses were rated as 0.79, assessed using advanced cross-correlation analysis, indicating the model exhibits good biofidelity. The model was then used to evaluate soft tissue response in frontal impact scenarios ranging from 8G to 22G in severity. Disc strains were highest in the C4-C5-C6 segments, and ligament strains were greatest in the ISL and LF ligaments. Both ligament and disc fiber strain levels exceeded the failure tolerances in the 22G case, in agreement with existing data. This study demonstrated that a cervical spine model can be developed at the tissue level and provide accurate biofidelic kinematic and local tissue response, leading to injury prediction in automotive crash scenarios.

Cervical Spine Model to Predict Capsular Ligament Response in Rear Impact

Predicting neck kinematics and tissue level response is essential to evaluate the potential for occupant injury in rear impact. A detailed 50th percentile male finite element model, previously validated for frontal impact, was validated for rear impact scenarios with material properties based on actual tissue properties from the literature. The model was validated for kinematic response using 4g volunteer and 7g cadaver rear impacts, and at the tissue level with 8g isolated full spine rear impact data. The model was then used to predict capsular ligament (CL) strain for increasing rear impact severity, since CL strain has been implicated as a source of prolonged pain resulting from whiplash injury. The model predicted the onset of CL injury for a 14g rear impact, in agreement with motor vehicle crash epidemiology. More extensive and severe injuries were predicted with increasing impact severity. The importance of muscle activation was demonstrated for a 7g rear impact where the CL strain was reduced from 28 to 13% with active muscles. These aspects have not previously been demonstrated experimentally, since injurious load levels cannot be applied to live human subjects. This study bridges the gap between low intensity volunteer impacts and high intensity cadaver impacts, and predicts tissue level response to assess the potential for occupant injury.

Influence of material properties on the ballistic performance of ceramics for personal body armour

In support of improved personal armour development, depth of penetration tests have been conducted on four different ceramic materials including alumina, modified alumina, silicon carbide and boron carbide. These experiments consisted of impacting ceramic tiles bonded to aluminum cylinders with 0.50 caliber armour piercing projectiles. The results are presented in terms of ballistic efficiency, and the validity of using ballistic efficiency as a measure of ceramic performance was examined. In addition, the correlation between ballistic performance and ceramic material properties, such as elastic modulus, hardness, spall strength and Hugoniot Elastic Limit, has been considered.

Investigation of whiplash injuries in the upper cervical spine using a detailed neck model

Whiplash injuries continue to have significant societal cost; however, the mechanism and location of whiplash injury is still under investigation. Recently, the upper cervical spine ligaments, particularly the alar ligament, have been identified as a potential whiplash injury location. In this study, a detailed and validated explicit finite element model of a 50th percentile male cervical spine in a seated posture was used to investigate upper cervical spine response and the potential for whiplash injury resulting from vehicle crash scenarios. This model was previously validated at the segment and whole spine levels for both kinematics and soft tissue strains in frontal and rear impact scenarios. The model predicted increasing upper cervical spine ligament strain with increasing impact severity. Considering all upper cervical spine ligaments, the distractions in the apical and alar ligaments were the largest relative to their failure strains, in agreement with the clinical findings. The model predicted the potential for injury to the apical ligament for 15.2 g frontal or 11.7 g rear impacts, and to the alar ligament for a 20.7 g frontal or 14.4 g rear impact based on the ligament distractions. Future studies should consider the effect of initial occupant position on ligament distraction.

Prediction of the failure pressure for complex corrosion defects

A new method for predicting the failure pressure of corrosion defects in pipelines has been developed. The failure pressure of a plain pipe represents an upper limit for the failure pressure of a pipe with a corrosion defect. The failure pressure of a uniform depth, infinitely long groove, where the depth is equal to the maximum depth of the corrosion defect, represents a lower limit for the failure pressure of a pipe with a natural corrosion defect. The predicted failure pressure can be calculated from these limits using the weighted depth difference (WDD) method, which accounts for the defect geometry and any interaction with adjacent defects. The WDD method has been validated using the results of 40 burst tests of pipe sections containing real corrosion defects. The results indicate that this method provides more accurate burst pressure predictions than the currently accepted corrosion defect assessment procedures.

Investigation of Head Response to Blast Loading

BACKGROUND Head injury resulting from blast loading, specifically mild traumatic brain injury, has been identified as a possible and important blast-related injury for soldiers in modern conflict zones. A study was undertaken to evaluate head response to blast loading scenarios using an explicit finite element numerical model and to comment on the potential for head injury. METHODS The blast loading and simplified human body numerical models were validated using impulse, peak acceleration and the Head Injury Criterion from experimental blast test data. A study was then undertaken to evaluate head response at varying distances and orientations from the explosive. RESULTS The accelerations and injury metrics for the head increased with decreasing distance to the explosive, as expected, but were also significant at intermediate distances from the explosive for larger charge sizes and intermediate heights of burst. Varying lateral position with constant standoff did not have a significant effect on the head kinematic response. CONCLUSIONS The head injury criteria considered were exceeded in close proximity to the explosive (<35 charge radii) and depended on the height of burst for the range of charge sizes considered. The injury criteria were also exceeded at intermediate distances for larger charge sizes because of the influence of the mach stem. Although the injury criteria used in this study are typically applied to longer duration events, and may not be applicable for shorter duration blast loading, aggressive loading is predicted at small standoff distances and confirmed by the resulting head kinematics.

Strain rate dependent properties of human craniovertebral ligaments

Craniovertebral ligaments were tested to failure under tensile loading. Ligaments tested included: transverse ligament, anterior atlanto occipital membrane, posterior atlanto occipital membrane, capsular ligaments between Skull-C1 and C1-C2, anterior atlantoaxial membrane, posterior atlantoaxial membrane and the tectorial membrane/vertical cruciate/apical/alar ligament complex. The objective of this study was to obtain mechanical properties of craniovertebral ligaments of a younger population, at varying strain rates representative of automotive crash scenarios, and investigate rate and gender effects for use in numerical models of the cervical spine. There have been few studies conducted on the mechanical properties of human craniovertebral ligaments. Only one study has tested all of the ligaments, and previous studies use older age specimens (mean age 67, from most complete study). Further, tests were often not performed at elongation rates representative of car crash scenarios. Previous studies did not perform tests in an environment resembling in vivo conditions, which has been shown to have a significant effect on ligament tensile behaviour. Fifty-four craniovertebral ligaments were isolated from twenty-one spines, and tested to failure in tension under simulated in vivo temperature and hydration levels, at quasi-static (0.5 s(-1)) and high strain rates (150 s(-1)). Values for failure force, failure elongation, stiffness, and toe region elongation were obtained from force-displacement curves. Values were analyzed for strain rate and gender effects. Increased strain rate produced several significant effects including: higher failure forces for the transverse ligament and capsular ligament (Skull-C1), lower failure elongation for the tectorial membrane complex, higher stiffness for the tectorial membrane complex and capsular ligament (Skull-C1), and lower toe region elongation for capsular ligament (Skull-C1). Gender effects were limited. Ligament tests demonstrated expected rate effects. Younger specimens had a higher failure force and stiffness and failed at lower elongations than older specimens from previous studies. Gender effects suggest there may be a difference between male and female properties, but require further testing to establish greater significance.

Experimental Database for Corroded Pipe: Evaluation of RSTRENG and B31G

The evaluation and development of the current corrosion defect assessment procedures for pipelines has been based on experimental burst tests of line pipe. In these tests, external corrosion has often been simulated with machined defects of simple geometry. As a result, assessment procedures which model the corrosion defect geometry with only a few parameters, such as ASME B31G, show reasonable agreement with the experiments. However, the degree of conservatism in these assessment methods is undefined when they are applied to complex corrosion defects. The authors have burst over 40 pipes removed from service due to corrosion defects. All corrosion defects on each pipe were measured in detail and the material properties were determined from tensile tests. The currently accepted assessment procedures for corroded line pipe (B31G and RSTRENG) have been applied to the database. The degree of conservatism in these procedures is quantified and a statistical model for the failure predictions is proposed.Copyright