Effective in-plane elastic properties of honeycomb-polymer composites

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.

Cell Wall Fracture Mechanism in Ultrasonic Assisted Cutting of Honeycomb Materials

Revealing the ultrasonic cutting mechanism of honeycomb composite is important for determining the acoustic parameters of the ultrasonic system and selecting the parameters of the cutting process. Understanding more details of the stress on the cell wall from ultrasonic vibrating tool and the conditions for cell wall breakage is essential to study the machining mechanism. According to the evolution of contact state between the straight edge cutter and the honeycomb cell wall in a cycle, the cutting force acting on the cell wall is divided into three stages: transverse cutting load action, longitudinal cutting load action, and no cutting load action. The cell wall deflection and stress equations under transverse cutting load were established by applying elastic thin plate small deflection theory. The deformation and fracture characteristics of the honeycomb cell wall were analyzed by combining the analytical and the finite element model. The results showed that the ultrasonic vibration of the cutter greatly improved the stiffening effect of the cell wall and its fracture was caused by the deflection under the transverse cutting load, which exceeded the maximum allowable deformation after local stiffening. In addition, with only longitudinal cutting load, it was difficult to break the critical buckling state that leads to cell wall fracture.

Performance Testing of L-PBF Produced Honeycombs Out of IN625

Laser Powder Bed Fusion (L-PBF) enables the production of complex metallic parts. Processes using pulsed wave (PW) laser radiation have been proven to be well suited to build thin-walled honeycomb structures. However, the behavior of these structures under load conditions remains mostly unexplored. The objective of this paper is to characterize L-PBF produced honeycombs by investigating their rub and leakage performance. A pulse modulated process based on previous studies is optimized for productivity and used to build L-PBF test samples out of Inconel 625 (IN625). The honeycomb cell geometry is adjusted for improved printability of the overhanging walls. Repeatable L-PBF production of honeycombs with a wall thickness of about 100 μm is confirmed. Conventionally manufactured honeycomb samples out of sheet metal are tested as reference. The rub experiments cover radial incursion rates of up to 0.5 mm/s and relative velocities of up to 165 ms−1 at incursion depths (ID) between 0.5 and 2.0 mm. Lower incursion forces are observed for the L-PBF components, with a higher degree of abrasion. The leakage tests examine the mass flow rate for pressure ratios between 1.05 and 2.0 at constant gap size and constant back pressure. The L-PBF honeycomb seals show a higher mass flow rate, with the slightly larger cell size and higher surface roughness appearing to be the main influencing factors. Overall, improved rubbing behavior and 10 % higher leakage than the conventional probes demonstrate the applicability of L-PBF for honeycomb sealing systems. Future performance improvements through dedicated L-PBF designs can be expected.

Lightweight Panel for Building Construction Based on Honeycomb Paper Composite/Core-Fiberglass Composite/Face Materials

Lightweight panels for indoor constructions are typically made from composite materials with honeycomb and corrugated structures. The reinforcements are used in this study, one is fiberglass and the other is cellulose fiber, which cellulose from recycled paper. Experimental results indicate that the weight of honeycomb paper panel is light, only 13.6% of fiberglass composite and 32.6% of plywood. The presence of honeycomb structure has a significant effect on mechanical behaviors of composite panels. Both flexural and compressive strengths increase by replacing corrugated structure into honeycomb structure. During compression, the compressive strength and modulus of two-layer honeycomb/core panel are higher than those of monolayer honeycomb/core. Particularly, the honeycomb cell-wall thickness has a little effect on the weight, but has an important effect on mechanical properties. These results can be created low cost and lightweight environment-friendly panels by using recycled paper honeycomb structure.

Inverted Honeycomb Cell as a Reinforcement Structure for Building Soft Pneumatic Linear Actuators

In this article, the inverted honeycomb cell, known to exhibit an auxetic behavior, is considered to design two pneumatic linear actuators. The actuators are built using a combination of soft and rigid structures. They present complementary performances in terms of displacement, force, and stiffness. Experimental evaluations are conducted using prototypes produced using multimaterial additive manufacturing to combine soft and rigid materials with freedom of shape. The first actuator is inspired by origami structures. The possibility to obtain large deformations under low pressure is observed. The second actuator is based on a cylindrical auxetic structure based on the inverted honeycomb cell. Smaller deformation is reached but the design favors the off-axis stiffness, so the component can be integrated without any additional mechanical joint for translation. A discussion on the relative performances of these two actuators and their possible uses conclude the paper.

Mechanisms of Stiffening in Polymer-Filled Honeycomb Composites

Honeycomb composites are common materials in applications where a high specific stiffness is required. Previous research has found that honeycombs with polymer infills in their cells exhibit effective stiffnesses greater than the honeycomb or polymer alone. Currently, the state of analytic models for predicting the effective properties of these honeycomb polymer composites is limited, thus further research is needed to better characterize the behavior of these materials. In this work, a nonlinear finite element analysis was employed to perform parametric studies of a filled honeycomb unit cell with isotropic wall and infill materials. A pinned 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. Mechanisms by which the stiffness amplification occurs is studied through parametric studies, and the results are compared to current analytic models. 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 4,000 have been observed, with auxetic behavior achieved by tailoring of the HPC geometry. This research provides an important step toward understanding the design space and benefits of honeycomb polymer composites, and demonstrates the possibilities for variable stiffness structures when considering smart material infill materials.

Slumber in a cell: honeycomb used by honey bees for food, brood, heating… and sleeping

Sleep appears to play an important role in the lives of honey bees, but to understand how and why, it is essential to accurately identify sleep, and to know when and where it occurs. Viewing normally obscured honey bees in their nests would be necessary to calculate the total quantity and quality of sleep and sleep’s relevance to the health and dynamics of a honey bee and its colony. Western honey bees (Apis mellifera) spend much of their time inside cells, and are visible only by the tips of their abdomens when viewed through the walls of an observation hive, or on frames pulled from a typical beehive. Prior studies have suggested that honey bees spend some of their time inside cells resting or sleeping, with ventilatory movements of the abdomen serving as a telltale sign distinguishing sleep from other behaviors. Bouts of abdominal pulses broken by extended pauses (discontinuous ventilation) in an otherwise relatively immobile bee appears to indicate sleep. Can viewing the tips of abdomens consistently and predictably indicate what is happening with the rest of a bee’s body when inserted deep inside a honeycomb cell? To distinguish a sleeping bee from a bee maintaining cells, eating, or heating developing brood, we used a miniature observation hive with slices of honeycomb turned in cross-section, and filmed the exposed cells with an infrared-sensitive video camera and a thermal camera. Thermal imaging helped us identify heating bees, but simply observing ventilatory movements, as well as larger motions of the posterior tip of a bee’s abdomen was sufficient to noninvasively and predictably distinguish heating and sleeping inside comb cells. Neither behavior is associated with large motions of the abdomen, but heating demands continuous (vs. discontinuous) ventilatory pulsing. Among the four behaviors observed inside cells, sleeping constituted 16.9% of observations. Accuracy of identifying sleep when restricted to viewing only the tip of an abdomen was 86.6%, and heating was 73.0%. Monitoring abdominal movements of honey bees offers anyone with a view of honeycomb the ability to more fully monitor when and where behaviors of interest are exhibited in a bustling nest.

Effect of Rotation on Leakage and Windage Heating in Labyrinth Seals With Honeycomb Lands

One of the basic assumptions of the traditional labyrinth seal leakage calculation is that rotation has minimal or no effect on seal leakage. With the advancement of gas turbine technology, to achieve high performance, seals are run at tight clearances and very high rotational speeds. Due to tight clearances and high speeds, the temperature rise across the seal can be very significant in reducing the seal flow due to the Raleigh line effect. The influence of rotation on the flow dynamics inside the seal region has not previously been studied in detail. In this study the effect of rotation is studied for smooth and honeycomb cells at various seal clearances and rotational speeds. The main objective of this study is to understand the influence of rotation on seal leakage. However, the effect of rotation on swirl and windage heating is also investigated. For this study, the author leveraged the validated 3D computational fluid dynamics methodology for a stationary and rotating labyrinth from previous studies. However, before performing studies on rotation, the numerical modeling approach is benchmarked against experimental data on rotation with smooth stator lands by Waschka et al. The numerical predictions show good agreement with the experimental data. As the rotational speed increases, seal discharge coefficient remains constant until a critical rotational speed is reached. This critical speed is shown to depend non-dimensionally on the ratio of Taylor number to Reynolds number (Ta/Re). As Ta/Re increases above 0.1, seal discharge coefficient can reduce by up to 25% depending on the seal clearance, fin tip speed, and honeycomb cell size.