Browsing by Author "Albert, Devon Lee"
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- Biomechanical Responses of Human Surrogates under Various Frontal Loading Conditions with an Emphasis on Thoracic Response and Injury ToleranceAlbert, Devon Lee (Virginia Tech, 2018-06-04)Frontal motor vehicle collisions (MVCs) resulted in 10,813 fatalities and 937,000 injuries in 2014, which is more than any other type of MVC. In order to mitigate the injuries and fatalities resulting from MVCs, new safety restraint technologies and more biofidelic anthropomorphic test devices (ATDs) have been developed. However, the biofidelity of these new ATDs must be evaluated, and the mechanisms of injury must be understood in order to accurately predict injury. Evaluating the biomechanical response, injury mechanisms, and injury threshold of the thorax are particularly important because the thorax is one of the most frequently injured body regions in MVCs. Furthermore, sustaining a severe thoracic injury in an MVC significantly increases mortality risk. The overall objective of this dissertation was to evaluate the biomechanical responses of human surrogates under various frontal loading conditions. This objective was divided into three sub-objectives: 1) to evaluate the biofidelity of the current frontal impact ATDs, 2) to evaluate the effect of different safety restraints on occupant responses, and 3) to evaluate rib material properties with respect to sex, age, structural response, and loading history. In order to meet sub-objectives 1 and 2, full-scale frontal sled tests were performed on three different human surrogates: the 50th percentile male Hybrid III (HIII) ATD, the 50th percentile male Test Device for Human Occupant Restraint (THOR-M) ATD, and approximately 50th percentile male post-mortem human surrogates (PMHS). All surrogates were tested under three safety restraint conditions: knee bolster (KB), KB and steering wheel airbag (KB/SWAB), and knee bolster airbag and SWAB (KBAB/SWAB). The kinematic, lower extremity, abdominal, thoracic, and neck responses were then compared between surrogates and restraint conditions. In order to assess biofidelity, the ATD responses were compared to the PMHS responses. For both the kinematic and thoracic responses, the HIII and THOR-M had comparable biofideltiy. However, the HIII responses were slightly more biofidelic. The ATDs experienced similar lower extremity kinetics, but very different kinetics at the upper and lower neck due to differences in design. Evaluation of the different restraint conditions showed that the SWAB and KBAB both affected injury risk. The SWAB decreased head injury risk for all surrogates, and increased or decreased thoracic injury risk, depending on the surrogate. The KBAB decreased the risk of femur injury, but increased or decreased tibia injury risk depending on the surrogate and injury metric used to predict risk. In order to meet sub-objective 3, the tensile material properties of human rib cortical bone and the structural properties of whole ribs were quantified at strain rates similar to those observed in frontal impacts. The rib cortical bone underwent coupon tension testing, while the whole ribs underwent bending tests intended to simulate loading from a frontal impact. The rib material properties accounted for less than 50% of the variation observed in the whole rib structural properties, indicating that other factors, such as rib geometry, were also influencing the structural response of whole ribs. Age was significantly negatively correlated with the modulus, yield stress, failure strain, failure stress, plastic strain energy density, and total strain energy density. However, sex did not significantly influence any of the material properties. Cortical bone material properties were quantified from the ribs that underwent the whole rib bending tests and subject-matched, untested (control) ribs in order to evaluate the effect of loading history on material properties. Yield stress and yield strain were the only material properties that were significantly different between the previously tested and control ribs. The results of this dissertation can guide ATD and safety restrain design. Additionally, this dissertation provides human surrogate response data and rib material property data for the validation of finite element models, which can then be used to evaluate injury mitigation strategies for MVCs.
- Effects of Sex, Strain Rate, and Age on the Compressive and Tensile Material Properties of Human Costal CartilageNowinski, Hannah Marie (Virginia Tech, 2022-07-08)The objective of this study was to evaluate the effects of sex, loading rate, and age on the compressive and tensile material properties of human costal cartilage over a wide range of subject ages and sexes. Cylindrical compression samples and dog-bone shaped tension samples were tested to failure on a material testing system using target strain rates of 0.005 strain/s and 0.5 strain/s. Compression data were obtained from forty (n = 40) subjects (M = 26, F = 14) ranging in age from 11 – 69 years (Avg. = 39.1 ± 18.2 yrs.), and matched loading rate data were obtained for thirty-four (n = 34) samples. Tension data were obtained from forty-one (n = 41) subjects (M = 30, F = 11) ranging in age from 10 – 59 years (Avg. = 32.9 ± 14.9 yrs.), and matched loading rate data were obtained for seventeen (n = 17) samples. For both compression and tension, load and sample deflection data were collected and used to calculate stress and strain. For the compression data, the toe region was fit using a second-order polynomial, and the toe transition stress, toe transition strain, second-order polynomial coefficient A, and second-order polynomial coefficient B were calculated. In addition, the elastic modulus, ultimate stress, ultimate strain, and strain energy density (SED) were also calculated for each test. For the tension data, only the elastic modulus, ultimate stress, ultimate strain, and SED were calculated for each test. There were no effects of sex on the material properties for either method of loading or strain rate. Therefore, male and female data were combined for the age and loading rate analyses. For compression, toe transition stress, toe transition strain, A, elastic modulus, ultimate stress, and SED were all found to be significantly higher at 0.5 strain/s compared to 0.005 strain/s. For tension, no material properties were found to differ with respect to loading rate. Regarding the effects of age, toe transition stress, toe transition strain, A, B, ultimate stress, ultimate strain and SED were found to significantly decrease with advancing age for the 0.005 strain/s compression data. At 0.5 strain/s, toe transition stress, toe transition strain, elastic modulus, ultimate stress, ultimate strain, and SED all significantly decreased with advancing age. For tension, ultimate stress, ultimate strain, and SED were found to significantly decrease with advancing age at 0.005 strain/s and 0.5 strain/s. Comparing the two loading modes, the ultimate stress, elastic modulus, and SED were significantly higher in compression than in tension. For the compression samples, sample density and percent calcification were also obtained for each sample using physical measurements and micro-CT scans, respectively. However, since there were only a few samples with large calcifications, no meaningful trends were found. This is the first study of its kind to analyze the effects of sex, loading rate, and age on both the compressive and tensile material properties on human costal cartilage from such a wide range of subject ages. The results from this study can be used to develop more accurate finite element models of the human body, which will allow researchers to better evaluate human occupant response and injury risk in motor vehicle collisions for both young and old individuals.
- Investigating the Thoracic Biomechanical Responses of Rear Seated 50th Percentile Male Anthropomorphic Test Devices and Post Mortem Human Surrogates During Frontal Motor Vehicle CollisionsBianco, Samuel Thomas (Virginia Tech, 2023-07-14)Frontal motor vehicle collisions (MVCs) account for the majority of injuries and fatalities in MVCs according to the Fatality Analysis Reporting Systems (FARS). One of the most commonly injured regions of the body during MVCs is the thorax. While there are fewer adult passengers riding in the rear seat compared to the front seat, the number of adults in the rear seat may increase dramatically in the near future with the rise of ridesharing services and highly automated vehicles (HAVs). With the increase in exposure for adults riding in the rear seat, the safety of these passengers needs to be evaluated. Previous research has shown that occupant protection in the rear seat is disproportionately lower than that of the front seat in modern vehicles due to the focus on front seat occupants in both regulatory and market-driven crash tests. This has resulted in many of the occupant safety systems, e.g., pretensioners (PT), load limiters (LL), and airbags, being widely available in the front seat, but sparsely available in the rear seat. Anthropomorphic test devices (ATDs) have been developed to investigate occupant safety during frontal MVCs and can be utilized in the investigation of rear seat occupant injuries. However, the biofidelity and injury risk criteria used for these ATDs has only been validated when seated in the front seat. To validate the response and injury risk predictions of existing frontal ATDs in the rear seat it is necessary to generate new biomechanical data in the rear seat of modern vehicles. The purpose of this work is to quantify the biomechanical responses of two frontal ATDs, i.e., the Hybrid III and THOR-50M 50th percentile male ATDs, and 50th percentile male post mortem human surrogates (PMHS) seated in the rear seat of modern vehicles, which have various seat geometries and restraint types, during frontal MVCs. Emphasis is placed on comparisons between the thoracic responses of the three human surrogates e.g., thoracic deflection time histories, and thoracic injury risks, i.e., ATD injury risk prediction versus instances of PMHS injuries. A series of twenty-four frontal sled tests were first conducted with the HIII and THOR-50M ATDs seated in the rear seats of seven vehicle test bucks with varying seat geometries and two different restraint types. Three vehicles had advanced restraints while four had conventional restraints. Three different crash pulses were used derived from vehicle specific US New Car Assessment Program frontal crash data: Scaled (32kph), Generic (32kph), and NCAP85 (56kph). Thoracic injury metrics were not exceeded in the lower severity pulses for either ATD but were exceeded during some of the high severity tests. A matched comparison analysis between a front and rear seated Hybrid III 50th percentile male ATD is presented second that highlights the disparities between front and rear seat iii occupant safety of modern vehicles during frontal MVCs. The Hybrid III ATD data were used for this comparison. Thoracic injury risk was found to be higher for the rear seated HIII across all vehicles, while thoracic acceleration was lower in the rear than the front for some vehicles. PMHS thoracic responses and injury risk equations were then evaluated in four of the vehicles used for the ATD tests using the high severity sled pulse, i.e., NCAP85 (56kph). Thoracic acceleration and normalized deflection values were higher in vehicles with conventional restraints, and the location of maximum deflection was always inboard of the sternum. The resulting thoracic injuries ranged from AIS 3 to AIS 5. Additionally, there were a larger average number of rib fractures in vehicles with conventional restraints versus advanced restraints. A multi-point deflection injury risk equation predicted injury the best. However the less censored rib fracture data that were obtained suggest that all three of the injury equations evaluated could be improved. Lastly, the PMHS data were used to assess the similarities in thoracic response between the ATDs and PMHS. An objective rating metric was used for the response comparison. The HIII had a slightly better average score than the THOR-50M; however, the THOR-50M had a more biofidelic kinematic response during the tests. This analysis furthers the understanding of the effect of different occupant protection systems on thoracic injury risk in a rear seat environment and the biofidelity of frontal 50th percentile male ATDs in the rear seat.
- Occupant Responses of Relaxed and Braced 5th Percentile Female and 50th Percentile Male Volunteers during Low-Speed Frontal and Frontal-Oblique Sled TestsChan, Hana (Virginia Tech, 2023-07-05)The increased prevalence of crash avoidance technologies like autonomous emergency braking necessitates understanding of occupant responses during low-speed frontal pre-crash braking and low-severity crash events. Active human body models (HBMs) have emerged as valuable tools to evaluate occupant safety during these events, but must be validated with relevant volunteer data to accurately represent the responses of live occupants. The objective of this dissertation was to quantify the occupant responses of relaxed and braced 5th percentile female and 50th percentile male volunteers during low-speed frontal and frontal-oblique sled tests designed to simulate pre-crash braking and low-severity crash events. A study comprised of 160 low-speed sled tests was performed with 20 volunteers. The volunteers' kinematics, kinetics, and muscle responses were compared to determine how altering impact direction (frontal and frontal-oblique), impact severity (1 g and 2.5 g), demographic group (mid-size male and small female), and muscle state (relaxed and braced) affected occupant responses. The volunteers' occupant responses were significantly affected by impact direction, impact severity, demographic group, and muscle state. The frontal-oblique tests resulted in greater leftward excursions compared to the frontal tests. Increasing the pulse severity resulted in greater forward excursions, reaction forces, and muscle activation. The male volunteers exhibited greater forward excursions and reaction forces compared to the female volunteers. However, the two demographic groups exhibited similar muscle activation during the sled tests. Bracing increased the volunteers' initial joint angles, muscle activation, and reaction forces prior to the sled tests. Bracing decreased forward excursions and increased reaction forces during the sled tests. The relaxed volunteers exhibited greater relative changes in occupant responses compared to the braced volunteers. Overall, this study demonstrated that muscle activation significantly affected the volunteers' kinematics, kinetics, and muscle responses for both mid-size males and small females during low-speed events. Observed differences between demographic groups were more prominent when relaxed and more diminished when braced. These results underscore the importance of validating active HBMs with relevant volunteer data in order to be more representative of live occupants for a wider range of demographic groups in varying muscle states. Finally, this dissertation provides a large, comprehensive, and novel biomechanical dataset that can be used to develop and validate active HBMs for use in assessing occupant response during frontal pre-crash braking and low-severity crash events. These models will help improve the understanding of potential injury risk and development of effective vehicle safety systems for use during low-speed events.
- Structural Design Inspired by the Multiscale Mechanics of the Lightweight and Energy Absorbent CuttleboneLee, Edward Weng Wai (Virginia Tech, 2023-11-03)Cuttlebone, the endoskeleton of cuttlefish, offers an intriguing biological structural model for designing low-density cellular ceramics with high stiffness and damage tolerance. Cuttlebone is highly porous (porosity ~93%) and lightweight (density less than 20% of seawater), constructed mainly by brittle aragonite (95 wt%), but capable of sustaining hydrostatic water pressures over 20 atmospheres and exhibits energy dissipation capability under compression comparable to many metallic foams (~4.4 kJ/kg). Here we computationally investigate how such a remarkable mechanical efficiency is enabled by the multiscale structure of cuttlebone. Using the common cuttlefish, Sepia Officinalis, as a model system, we first conducted high-resolution synchrotron micro-computed tomography (µ-CT) and quantified the cuttlebone's multiscale geometry, including the 3D asymmetric shape of individual walls, the wall assembly patterns, and the long-range structural gradient of walls across the entire cuttlebone (ca. 40 chambers). The acquired 3D structural information enables systematic finite-element simulations, which further reveal the multiscale mechanical design of cuttlebone: at the wall level, wall asymmetry provides optimized energy dissipation while maintaining high structural stiffness; at the chamber level, variation of walls (number, pattern, and waviness amplitude) contributes to progressive damage; at the entire skeletal level, the gradient of chamber heights tailors the local mechanical anisotropy of the cuttlebone for reduced stress concentration. Our results provide integrated insights into understanding the cuttlebone's multiscale mechanical design and provide useful knowledge for the designs of lightweight cellular ceramics. Upon the prior curvature analysis of the cuttlebone walls, we discovered that the walls were primarily "saddle-shaped". Thus, the characterization of different curvatures, varying between flat, domed, saddled, or cylindrical surfaces, were explored. A mathematical model was utilized to generate multiple walls with different curvature characteristics. We observed the mechanical performance of these walls via finite-element analysis and formulated different techniques for designing effective ceramic structures through incorporation of curvature.
- Tensile Material Properties of Human Costal Cartilage PerichondriumDamron, Julia Anne (Virginia Tech, 2024-05-31)Rib and costal cartilage fractures are the most common injuries resulting from blunt thoracic loading scenarios, including motor vehicle collisions. The costal cartilage is a cylindrical hyaline cartilage composed of two layers: a core interstitial matrix enveloped by the perichondrium. The perichondrium itself has an inner chondrogenic layer and an outer fibrous layer. The objective of this study was to evaluate the tensile material properties of human costal cartilage perichondrium at two loading rates for a range of subject demographics. Fifty-six (n=56) samples containing the fibrous layer and chondrogenic layer (i.e., two-layered samples) were fabricated from thirty-three (n=33) donors aged from 11 to 69 years of age (19 M, 14 F). Thirteen (n=13) samples without the fibrous layer (i.e., one-layered samples) were fabricated from eight (n=8) donors aged from 11 to 54 years of age (5 M, 3 F). The perichondrium was isolated from the interstitial matrix for all samples and the fibrous layer was removed for one-layered samples to assess the effect of the absence of the fibrous layer. The tissue was then stamped into a dog bone-shaped coupon and sanded down to a uniform thickness of ~1.3 mm for two-layered samples and ~1 mm for one-layered samples. The gage length of the completed coupons was marked with a black ink dot pattern to facilitate strain calculations via video tracking. The coupons were loaded axially in tension to failure at either a slow (0.005 s⁻¹) or fast (0.5 s⁻¹) target loading rate using a material testing system. The elastic modulus, ultimate stress, ultimate strain, failure stress, failure strain, and strain energy density (SED) were then calculated for each test. Material property data were compared by sample type and loading rate. Since there was no significant influence of sex on any material properties, the data were grouped together for the analysis. Modulus, ultimate stress, failure stress, and SED were found to significantly decrease with donor age at both loading rates and ultimate and failure strain also significantly decreased with donor age at the 0.5 s⁻¹ target loading rate. Failure stress in the two-layered samples was found to be greater than that of the one-layered samples at both loading rates. One-layered samples had a greater failure strain than two-layered samples at both loading rates. Perichondrium data were compared to interstitial matrix data from a previous study to further investigate the role of cartilage layer on material properties. The modulus, ultimate stress, and failure stress of costal cartilage decreased moving radially inward (greatest in two-layered perichondrium samples, least in interstitial matrix samples). The opposite was true for ultimate and failure strain, with the greatest failure strain values occurring in the interstitial matrix and the least in the two-layered perichondrium samples. The sample size of one-layered samples was too small to draw any substantial conclusions regarding age trends. This was the first study to analyze the material property trends in costal cartilage perichondrium. The results of this study can be incorporated into virtual human body models to improve the accuracy of thoracic injury prediction in the context of motor vehicle safety.