Every year, 14 to 41 cases per 100,000 infants under 1 year old are diagnosed with inflicted head injury (IHI), primarily resulting from shaking trauma (IHI-ST) or blunt force trauma. Without reliable structural bending stiffness data of the infant’s neck, injury predictions usin
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Every year, 14 to 41 cases per 100,000 infants under 1 year old are diagnosed with inflicted head injury (IHI), primarily resulting from shaking trauma (IHI-ST) or blunt force trauma. Without reliable structural bending stiffness data of the infant’s neck, injury predictions using physical infant surrogates in shaking simulations remain highly uncertain, undermining both forensic and preventive studies. Due to ethical constraints, biomechanical properties of infant necks are scarce, limiting the biofidelity and validation possibilities for existing infant surrogates, such as anthropomorphic test dummies (ATDs). Currently, infant neck surrogates suffer from inadequate biofidelity concerning stiffness and validated range of motion, necessary to accurately simulate shaking trauma simulations.
This thesis aims to address the gap by exploring the design of a durable, adjustable stiffness surrogate neck, improving the accuracy of shaking experiments. Experimental stiffness values obtained from functional spine units (FSU) by Luck et al., extrapolated by Sullivan et al. were used as target values, suggesting stiffness ranges of 0.2 Nm/rad in flexion and 0.4 Nm/rad in extension for a 1.5-month-old infant. The design aims for a 90-degree ROM in flexion and extension, essential for accurate simulation of chin-to-chest and occiput-to-back contacts, both critical for assessing injury mechanisms.
A compliant monolithic hinge mechanism from Fowler et al. was proposed as the core mechanism, able to achieve large angular displacements through flexures. Finite element analysis was performed to optimize material and geometric parameters. Parametric modeling in ABAQUS identified the relationships between stiffness, stress, material properties, and hinge geometry. Based on these relationships, feasible prototype geometries were extracted, varying in flexure thickness, length, and width. Manufacturing was done using 3D printing with polylactic acid (PLA) and carbon fiber-reinforced polyethylene terephthalate glycol (PETG-CF).
Static experimental validation demonstrated achievable stiffness values at the lower boundary of target ranges while the upper bound was not reached, primarily due to anisotropy from 3D printing and material limitations. Despite these limitations, prototypes successfully reached the targeted ROM. Future research should incorporate dynamic testing to validate durability and head kinematics and should consider multi-degree-of-freedom designs to fully replicate infant neck biomechanics. Further challenges remain in replicating infant neck viscoelasticity and obtaining experimental infant data for validation.