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Changes in limb volume and shape among transtibial amputees affects socket fit and comfort. The ability to accurately measure residual limb volume and shape and relate it to comfort could contribute to advances in socket design and overall care. This work designed and validated a novel 3D laser scanner that measures the volume and shape of residual limbs. The system was designed to provide accurate and repeatable scans, minimize scan duration, and account for limb motion during scans. The scanner was first validated using a cylindrical body with a known shape. Mean volumetric errors of 0.17% were found under static conditions, corresponding to a radial spatial resolution of 0.1 mm. Limb scans were also performed on a transtibial amputee and yielded a standard deviation of 8.1 ml (0.7%) across five scans, and a 46 ml (4%) change in limb volume when the socket was doffed after 15 minutes of standing. [ABSTRACT FROM AUTHOR]

Honeycomb materials as reinforcements for shape memory polymers have been considered for their commercial availability, ease of geometric tailoring, and high in-plane stiffnesses. The design optimization of these honeycomb cells remains an open field of research, with many approaches taken in formulating the structural optimization problems. This investigation focuses on implementing a shape variable parametrization of the honeycomb to study the possible value of both cell asymmetry and spatially varying cell geometries in multicell networks. A unit cell finite element model framework was developed to predict the in-plane elastic properties of these composites, and two design objectives were selected to be optimized. Pareto fronts were estimated for multiple loading cases and cell wall material models, and experimental results were collected for model validation. The optimization results find that these composites can achieve a large range of performances, with maximum moduli as high as 17.2 GPa. Large asymmetry is found in the optimized cell geometries, and relationships are identified between loading cases and for different wall materials. Furthermore, the experimental results validate the finite element model predictions, with relative errors as low as 20% for the predicted maximum modulus and 2% for the modulus ratio. [ABSTRACT FROM AUTHOR]

Polymer‐filled honeycomb composites are composite materials that exhibit effective in‐plane moduli greater than either the honeycomb or polymer alone. Previous numerical modeling work by the authors has identified two key mechanisms by which this stiffness amplification is achieved. For thin honeycomb cells, the difference in Poisson's ratio between the infill and honeycomb drives the in‐plane composite behavior. For large cell depths, the volume change of the hexagonal cells, acting on the infill polymer, is the dominant factor in stiffness amplification. This work aims to extend these findings to thick walled honeycombs, and to experimentally validate the model predictions while making comparisons to existing analytic models. A unit cell finite element model is created for the composite, with isotropic material properties for the honeycomb and infill obtained from characterization tests on 3D printed honeycomb wall material and polyurethane elastomer infill materials. An experimental investigation is completed, where both empty and polymer filled honeycomb samples are 3D printed and tested for a range of cell geometries, varying the cell angle, cell depth, and infill polymer, and are testing in two in‐plane loading directions. The results support both the model predictions of the effective Young's moduli and the mechanisms of stiffness amplification previously found, with a maximum percent error of 16.9% found and an amplification factor of the infill modulus of up 16 demonstrated. The improved understanding demonstrated in this work supports the use of these composites in applications where reinforcement of the honeycomb by a polymer, or vice versa, is desired. [ABSTRACT FROM AUTHOR]

Space-based adaptive optic systems have gained considerable attention within the past couple of decades. Achieving the increasingly stringent performance requirements for these systems is greatly hindered by strict weight restrictions, size limitations, and subjected hostile environments. There has been considerable attention in developing lightweight adaptive optics where piezoelectric sheet actuators are attached' on the back of optical mirrors to achieve a high precision surface shape with minimum additional weight. Vibration control of such large flexible space structures is continually challenging to engineers due to the large number of actuators and sensors and the large number of vibration modes within the operational bandwidth. For these structures, any disturbed modes are likely to remain vibrating for an extended period of time due to the small amount of damping available. As a result, controller spillover should be minimized as much as possible to avoid exciting the residual modes. In recent investigations of circular plate shape control by [Philen and Wang, Int. Soc. Opt. Eng. 4327, pp. 709-719]. It was demonstrated that directional decoupling of the two-dimensional actuator (meaning that the actuation in one of the two directions is eliminated) improves the system performance when correcting for the lower order Zernike static deformations. This directional decoupling effect can be achieved through an active stiffener (AS) design. In this research, analytical and experimental efforts are carried out to examine the effect of the active stiffener actuators in reducing the controller spillover through the stiffeners' decoupling characteristics. It is shown that significant reductions in controller spillover can be achieved in systems using the active stiffener actuators when compared to systems having direct attached (DA) actuators, thus resulting in improved vibration control performance. The experimental results verify the analytical predictions and clearly demonstrate the merit of the active stiffener concept. [DOI: 10.1115/1.2013303]

Spaced-based adaptive optic systems have gained considerable attention within the past couple of decades. Achieving the increasingly stringent performance requirements for these systems is greatly hindered by strict weight restrictions, size limitations, and subjected hostile environments. There has been considerable attention in lightweight adaptive optics, where piezoelectric sheet actuators are directly attached on the back of optical mirrors to achieve a high-precision surface shape with minimum additional weight. In recent studies, it was discovered that the performance of the system could be further improved if the piezoelectric sheet actuator were decoupled in direction, meaning that the actuation in one of the two directions is eliminated. To realize the decoupling effect, the concept of utilizing the active stiffener for high-precision shape control is proposed and investigated in the study. The active stiffener is a stiffener-piezoceramic actuator pair that consists of an passive insert (stiffener) placed between the host structure and the active piezoelectric actuator. The basic premise is that the insert (stiffener) will reduce the action transmitted in one direction while allowing adequate action to transmit in the orthogonal direction. In this research, analytical and experimental efforts are carried out to examine the effect of the active stiffener actuators for shape control of circular plate structures. Analysis is performed on two large flexible circular plate structures, one having the direct attached actuators and the other utilizing the active stiffener actuators. It is shown that more reductions in the surface error can be achieved with the active stiffeners, as compared to systems with the direct attached actuators. It is illustrated that the direct attached actuators generate more localized deformation in the structure, whereas the decoupling capability of the active stiffener reduces the undesired localized deformation considerably. The experimental results verify the analytical predictions and clearly demonstrate the performance improvement of the active stiffener concept over the direct attached actuator.

Honeycomb composites are now common materials in applications where high specific stiffness is required. Previous research has found that honeycombs with polymer infills in their cells, here referred to as honeycomb-polymer composites (HPCs), exhibit effective stiffnesses greater than the honeycomb or polymer alone. Currently, the state of analytic models for predicting the elastic properties of these composites is limited, and further research is needed to better characterize the behavior of these materials. In this research, a nonlinear finite element analysis was employed to perfor2m parametric studies of a filled honeycomb unit cell with isotropic wall and infill materials. A rigid wall model was created as an upper bound on the deformable wall model's performance, and an empty honeycomb model was employed to better understand the mechanisms of stiffness amplification. Parametric studies were completed for infill material properties and cell geometry, with the effective Young's modulus studied in two in-plane material directions. The mechanisms by which the stiffness amplification occurs are studied, and comparisons to existing analytic models are made. It has been observed that both the volume change within the honeycomb cell under deformation and the mismatch in Poisson's ratios between the honeycomb and infill influence the effective properties. Stiffness amplifications of over 4000 have been observed, with auxetic behavior achieved by tailoring of the HPC geometry. Additionally, the effect of large effective strains up to 10% is explored, where the cell geometry changes significantly. This research provides an important step toward understanding the design space and benefits of HPCs. [ABSTRACT FROM AUTHOR]