Benjamin P.J. Hasseldine

‘MotorcycleSim’: An Evaluation of Rider Interaction with an Innovative Motorcycle Simulator

This paper describes a user-centred design process that has been used to develop an innovative simulator for research into motorcycle ergonomics and rider human factors. Building on initial user requirements and user experience elicitation exercises, an evaluation was conducted to investigate specificissuesassociatedwithsimulatorfidelity.Anexperimentalapproachwasemployedtoexamine the physical and functional fidelity of the simulator. Using different steering and visual feedback configurations, a battery of objective and subjective dependent variables were analysed including: user perceptions and preferences, rider performance data, rider workload, rider comfort issues and thefirstevaluationofsimulatorsicknessforamotorcyclesimulator.Theresultsindicatedthatacrossa number of measures, aspects of functional fidelity were considered more important than the physical fidelity of the simulator. This evaluation takes the development of the simulator a stage further and the paper provides recommendations for future improvements.

Compression-After-Impact of Sandwich Composite Structures: Experiments and Simulation

A combined experimental and numerical study of compression-after-impact strength of honeycomb core sandwich composite panels is described. Barely-visible impact damage was induced using quasi-static indentation. Specimens consisted of 16-ply carbon-epoxy facesheets with an aluminum honeycomb core. The facesheet stacking sequence, core geometry and thickness were varied as was the indentor diameter to study the effect of these parameters on damage resistance and post-impact damage tolerance. Computational models of the quasi-static indentation and compression after impact are underway. Results to date compare the experimental and simulate indentations for 25.4 mm diameter indentors. Future work will include modeling the larger, 76.2 mm indentor as well as compression-after-impact.

Mechanical response of common millet (Panicum miliaceum) seeds under quasi-static compression: Experiments and modeling

The common millet (Panicum miliaceum) seedcoat has a fascinating complex microstructure, with jigsaw puzzle-like epidermis cells articulated via wavy intercellular sutures to form a compact layer to protect the kernel inside. However, little research has been conducted on linking the microstructure details with the overall mechanical response of this interesting biological composite. To this end, an integrated experimental-numerical-analytical investigation was conducted to both characterize the microstructure and ascertain the microscale mechanical properties and to test the overall response of kernels and full seeds under macroscale quasi-static compression. Scanning electron microscopy (SEM) was utilized to examine the microstructure of the outer seedcoat and nanoindentation was performed to obtain the material properties of the seedcoat hard phase material. A multiscale computational strategy was applied to link the microstructure to the macroscale response of the seed. First, the effective anisotropic mechanical properties of the seedcoat were obtained from finite element (FE) simulations of a microscale representative volume element (RVE), which were further verified from sophisticated analytical models. Then, macroscale FE models of the individual kernel and full seed were developed. Good agreement between the compression experiments and FE simulations were obtained for both the kernel and the full seed. The results revealed the anisotropic property and the protective function of the seedcoat, and showed that the sutures of the seedcoat play an important role in transmitting and distributing loads in responding to external compression.

Damage resistance of aluminum core honeycomb sandwich panels with carbon/epoxy face sheets:

The damage resistance of composite sandwich structures with eight and 16 ply quasi-isotropic, carbon/epoxy face sheets and aluminum honeycomb core is evaluated. The external damage is induced quasi-statically, using spherical steel indentors under displacement control, to be in the vicinity of the barely visible threshold. In addition to the face sheet thickness, other parameters that are varied include the core thickness, core density, face sheet layup, and indentor diameter. The effect of these parameters on the extent of damage is evaluated using the damage metrics of dent depth, dent diameter, and planar area of delamination. When dent depth or dent diameter is considered as the damage metric, specimens containing a higher density core are always found to be the most damage resistant. When planar area of delamination is considered as the damage metric, the eight ply configuration comprised of a lower density core and face sheets containing only small ply angle changes are found to be the most damage resistant. However, this configuration is found to be the least damage resistant when this damage metric is applied to the 16 ply specimens. Rather, the best delamination resistance is provided by a 16 ply configuration with a high density core and face sheets that have ±45° ply groups at the beginning and ending of their stacking sequence.

Compressive strength of aluminum honeycomb core sandwich panels with thick carbon–epoxy facesheets subjected to barely visible indentation damage:

An experimental study of damage tolerance under quasi-static indentation (QSI) was performed for sandwich composite panels consisting of 16-ply carbon–epoxy facesheets bonded to an aluminum honeycomb core. To determine how indentation damage and compression strength after indentation depend on the facesheet layup, three facesheet stacking sequences were used, varying the maximum ply angle change and placement of the outermost 0° ply. Similarly, to determine the effect of core parameters on damage and strength following indentation, three cores with varying density and thickness were studied. Specimens were indented in QSI to the barely visible indentation damage threshold by spherical indenters of 25.4 or 76.2 mm diameters. Damaged specimens were tested to failure in compression to determine the post-indentation compressive strength and resulting failure mode. Compression-after-indentation (CAI) strength is compared to the undamaged strength obtained from edgewise-compression tests of specimens with the same geometry type. Three distinct failure modes were observed in the CAI experiments: compressive fiber failure, delamination buckling and global instability. Post-indentation compressive strength was independent of indenter size and there was no clear propensity for a particular failure mode dependent on a given specimen geometry. Specimens with a high core density and facesheets with a primary ply angle change of 90° were found to be the most damage resistant. Specimens with facesheets having the outer 0° plies closest to the center of the laminate were found to be the most damage tolerant.

Amplifying Strength, Toughness, and Auxeticity via Wavy Sutural Tessellation in Plant Seedcoats

Protective armors are widespread in nature and often consist of periodic arrays of tile-like building blocks that articulate with each other through undulating interfaces. To investigate the mechanical consequences of these wavy tessellations, especially in instances where the amplitude of the undulations is near the scale of the constituent tiles as is found in the seedcoats of many plant species, an approach that integrates parametric modeling and finite element simulations with direct mechanical testing on their 3D-printed multi-material structural analogues is presented. Results from these studies demonstrate that these tiled arrays of largely isotropic star-like unit cells exhibit an unusual combination of mechanical properties including auxeticity and mutually amplified strength and toughness which can be systematically tuned by varying the waviness of the sutural tessellation.

An analytical model for the response of carbon/epoxy-aluminum honeycomb core sandwich structures under quasi-static indentation loading

An analytical model is developed to predict the loading and unloading response, as well as the residual dent diameter and dent depth, of carbon/epoxy-aluminum honeycomb core composite sandwich structures undergoing quasi-static indentation loading. The model considers damage created using spherical indenters and is valid up to the barely visible external damage threshold. The initial low load regime (until the onset of core crushing) is modeled using a combination of local Hertzian indentation of an elastic half-space and small deflection plate theory of a circular plate on an elastic foundation. For loads above those required to cause core crushing, the model uses the Rayleigh-Ritz method of energy minimization with the total system energy determined using a combination of face sheet bending energy, face sheet membrane energy and work done to the core during both elastic deformation and crushing. Degraded face sheet properties are used in the model beyond the onset of face sheet delamination, which is predicted using Griffith’s energy criterion. The model is validated using experimental results for sandwich structures consisting of quasi-isotropic 8- (thin) and 16- (thick) ply carbon/epoxy face sheets and aluminum honeycomb cores. The results show that the overall mechanics of the model are fundamentally correct and reflective of physical behavior. Thus, in its present form the model shows promise as a preliminary design tool.

Compression After Impact of Thick Sandwich Composite Structures

Sandwich composite structures offer benefits over monolithic composites with increased bending stiffness and strength, and reduced structural weight. However, sandwich panels are more susceptible to damage from low energy impact events, such as tool drops, which can result in internal damage barely or even undetectable during visual inspection. Left undetected such damage can significantly compromise the compressive strength. An experimental study of 16-ply carbon-epoxy facesheets adhered to an aluminum honeycomb core was studied to examine the resulting failure modes in compression and the damage tolerance to low-velocity impact by quasi-static indentation. Various facesheet stacking sequences and core geometries were studied to examine the effect of facesheet and core geometry on the damage tolerance. Undamaged strength was obtained by means of an edgewise compression (EC) test. The strength of damaged specimens was obtained by compression-after-impact (CAI) test on specimens subjected to barely-visible impact damage induced by indentation of either a 25.4 or 76.2 mm diameter spherical indentor. Residual dent depths and planar delamination area for use as damage metrics were obtained from non-destructive evaluation using C-scan. Dent depth and planar delamination area results showed that the core type had a significant influence on the resistance to damage, with the denser core being more damage resistant during quasi-static indentation. Compression after impact results showed that specimens exhibited three primary failure modes, fiber failure, delamination buckling or global instability of the indentation. Although particular facesheet / core geometries had higher propensities for a particular failure mode, no definitive trend for failure mode or compressive strength for either indentor size emerges from the data.