Shock Absorption Capability Research Articles

Experimental and Numerical Analysis of the Impact Resistance of Polyurethane Foam Aluminum-Concrete Sandwich Structures

The objective of this research paper is to examine the shock-absorption capabilities of sandwich structures that utilize polyurethane foam and aluminum as energy-absorbing materials. A series of drop weight impact tests were conducted on sandwich structures comprising polyurethane foam, aluminum, and concrete. The investigation encompasses variations in the thickness of the polyurethane foam-aluminum absorption layer, the impact height, and different structural combinations, coupled with numerical simulations. Results indicate that as the thickness of the polyurethane foam-aluminum energy absorption layer increases, the energy absorbed by the composite structure also increases. However, the rate of this increase tapers off as the layer thickness continues to grow. The impact height influences energy absorption within a defined range, enabling optimal utilization of the deformation and energy absorption capacities of the polyurethane foam-aluminum layer. Notably, the double-sandwich structure outperforms the single-sandwich structure in terms of impact resistance. The incorporation of the polyurethane foam-aluminum sandwich structure significantly enhances the impact resilience of concrete. Among the tested configurations, the double-sandwich structure composed of polyurethane foam, aluminum, and concrete exhibits the optimal absorption performance. Nevertheless, the layered nature of the structure significantly increases its construction complexity, potentially impacting the practical feasibility of utilizing the polyurethane foam-aluminum-concrete composite structure in real-world applications.

4D printing of biobased shape memory sandwich structures

Lightweight sandwich structures already have many applications in the aerospace, automotive, and construction sectors due to their high strength-to-weight ratio, enhanced stiffness and rigidity, and high energy and shock absorption capabilities. Additive manufacturing (AM) can provide great freedom and flexibility in the fabrication of complex sandwich structures that cannot be made by other conventional processes. The application of smart materials, like shape memory polymers (SMP), can offer the capability of dynamic transformation so that the deformed structure can recover its original shape using external stimuli, such as temperature. This study exploits the potential of this technology in the design and manufacturing of biobased smart sandwich structures with energy absorption capability and shape recovery performance. For that, a combination of recycled poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) biopolymers are developed as printing filaments with shape memory properties. The designed sandwich samples are fabricated by Fused Filament Fabrication (FFF) technology. The mechanical and functional properties of the printed samples are also evaluated. The results show PLA/PBS filaments have good printability and the fabricated parts have acceptable dimensional accuracy, mechanical strength, and functional performance.

Preparation and performance study of polyurethane/ kaolinite nanocomposite insulation materials

Abstract Polyurethane foam insulation materials exhibit excellent noise reduction, shock absorption and vibration damping capabilities while being cost-effective and easily moldable. They have found widespread applications in diverse fields such as automotive, machinery, packaging, insulation, healthcare and construction. However, the application range of this traditional organic material is limited by issues related to thermal stability and flame retardancy. By achieving uniform dispersion of nanoparticles, composite materials exhibit enhanced comprehensive properties in terms of flame retardancy, oxidation resistance, physicochemical stability and structural performance. Polyurethane/Kaolinite nanocomposite insulation materials were prepared by using the in situ intercalation compounding method. X-ray diffractometer, Fourier infrared spectrophotometer, thermogravimetric analyzer and scanning electron microscope were used to characterize the thermal stability of the composite material obtained under different preparation conditions and the state of the nanomaterial in the system. The results showed that the composite material with good dispersion of kaolinite in the matrix was obtained by effective surface modification through dimethyl sulfoxide. The doping of low-concentration kaolinite can improve the thermal stability of polyurethane. When the mass fraction of nano-kaolinite is 5%, the initial decomposition temperature of the composite system is 47°C higher than that of pure polyurethane and the system achieves the highest thermal stability.

A Shear-Stiffening Mouthguard with Excellent Shock Absorption Capability and Remoldability via a Dynamic Dual Network.

Mouthguards are used to reduce injuries and the probability of them to orofacial tissues when impacted during sports. However, the usage of a mouthguard is low due to the discomfort caused by the thickness of the mouthguard. Herein, we have constructed a dynamic dual network to fabricate a shear-stiffening mouthguard with remoldability, which are called remoldable shear-stiffening mouthguards (RSSMs). Based on diboron/oxygen dative bonds, RSSMs show a shear-stiffening effect and excellent shock absorption ability, which can absorb more than 90% of the energy of a blank. Even reducing the thickness to half, RSSMs can reduce approximately 25% of the transmitted force and elongate by about 1.6-fold the buffer time compared to commercial mouthguard materials (Erkoflex and Erkoloc-pro). What is more, owing to the dynamic dual network, RSSMs show good remolding performance with unchanged shear-stiffening behavior and impact resistance, which conforms to the existing vacuum thermoforming mode. In addition, RSSMs exhibit stability in artificial saliva and biocompatibility. In conclusion, this work will broaden the range of mouthguard materials and offer a platform to apply shear-stiffening materials to biomedical applications and soft safeguarding devices.

Shock absorption and dispersion capability of a novel five-layer mouthguard sheet material.

There is a growing need for a mouthguard sheet material with higher shock absorption and dispersion capacity than those obtained by conventional materials. A five-layer mouthguard sheet material was previously developed using laminated ethylene vinyl acetate and polyolefin copolymer resin. In this study, the shock absorption capacity and dispersion capability of the new sheet material were investigated and compared with those of other materials. Impact testing for the new sheet material showed that the force required to displace the sheet by 1 mm was significantly higher at all thicknesses (p<0.001), whereas the puncture energy and displacement were significantly lower than those for ethylene vinyl acetate (p<0.05). The five-layer mouthguard sheet material successfully absorbed and resisted shock. Therefore, the sheet material potentially increases resistance to applied deformation in teeth and alveolar bone and maintains structure. The five-layer sheet material could expand the range of mouthguard products and help prevent oral trauma.

Shock absorption capability of corrugated ring yield mount subjected to high impact loading

Various types of mechanical energy-absorbing devices are known that operate by plastic deformation. The corrugated ring mount that is used in this study relates to a device that absorbs energy by plastic deformation. This energy-absorbing device has reduced volumetric proportions, simple in design, and therefore has small overall dimensions and can be mass-produced at low cost. This study aims to determine the shock absorption capability and efficiency of this mount against impact loading. For this, Finite Element Method Analysis (FEA) and experimentation are done. The FEA is done using the Explicit Dynamics (AutoDyn) module of ANSYS Workbench and for experimentation Drop Test Machine (DTM) is used. In this study impact load from low g up to 85 g is applied and a very close agreement is found between FEA and experimental results. There is just a 5–10% deviation between the findings. The results show that this mount is plastically deformed to absorb the impact energy with a maximum efficiency of 70%. It concludes that it is a reliable and safer shock energy device.

Deformation analysis in impact testing of functionally graded foams by the image processing of high-speed camera recordings

We developed an image processing algorithm and applied it on high-speed camera recordings to characterize the deformation response of three-layered density-graded foam structures subjected to drop weight testing. Different densities (30, 40, 50 and 70 kg/m3) of weakly cross-linked polyethylene foam sheets were laminated together to achieve varying density distributions along the thickness, and the effect of layer order on the shock absorption capability was evaluated. Foam structures with a higher density top layer and a negative density gradient showed enhanced energy absorption in the initial stage of deformation, which resulted in lower maximum reaction forces. The positive effect of layer order modification was more dominant at higher impact energies. We provided a detailed explanation of the tendencies by investigating the differences in deformation propagation and the changes in the diameter of the deformation zone. The presented method can be utilized to design sports and packaging foam products.

Aluminium metal foam production methods, properties and applications- a review

Aluminium metal foam has a cellular structure. It's lightweight with these unique physical and mechanical properties and widely used in structural and functional applications. This paper's studies show the possible ways to produce Aluminium metal foam and its different properties and, based on that, the field it has applications. During the studies, it is observed that the Aluminium metal foam can develop in two ways: solid route and liquid route, after acquiring unique properties, such as light in weight to strength, suitable acoustic properties, and shock and energy absorption capabilities. The application will be selected based on properties and open or closed pore cells obtained in Aluminium metal foam. The significant finding from the review is that Aluminium metal foam has broad applications. However, the main lacunas that are still Aluminium metal foam are commercially not used because it is challenging to get good properties such as attaining uniform distribution and percentage of porosity in the prepared foam sample and uniform pore size. Another critical factor is that the cost will be high if the liquid or solid route develops the metal foam. So powder metallurgy process is the best method to produce metal foam to get better surface integrity and a proper network connection between each pore.

Hybrid auxetic materials implemented in crates & non-pneumatic wheels for shock absorption

In this study, new hybrid auxetic structures have been designed, and modifications of the pre-existing auxetic & hybrid auxetic structures have been made to analyze the shock absorption capability of the designed structures. The basic hybrid auxetic structure consists of a bowtie structure (exhibits auxetic property) which is partnered with a regular hexagon (for stability). The modifications are made to the hexagon along its vertices. On a few hybrid auxetic models, the bowtie is also significantly redesigned. These modifications result in the enhancement of the Negative Poisson's ratio as compared to the basic hybrid auxetic structure. In addition to that, they are also structurally stable than their predecessor. Depending upon their property & performance, it is determined whether to use them as support structures in the packaging (crates) or as the internal frame of non-pneumatic wheels.

The Dynamic Impact Response of 3D-Printed Polymeric Sandwich Structures with Lattice Cores: Numerical and Experimental Investigation.

This paper proposes a dynamic drop weight impact simulation to predict the impact response of 3D printed polymeric sandwich structures using an explicit finite element (FE) approach. The lattice cores of sandwich structures were based on two unit cells, a body-centred cubic (BCC) and an edge-centred cubic (ECC). The deformation and the peak acceleration, referred to as the g-max score, were calculated to quantify their shock absorption characteristic. For the FE results verification, a falling mass impact test was conducted. The FE results were in good agreement with experimental measurements. The results suggested that the strut diameter, strut length, number and orientation, and the apparent material stiffness of the lattice cores had a significant effect on their deformation behavior and shock absorption capability. In addition, the BCC lattice core with a thinner strut diameter and low structural height might lead to poor shock absorption capability caused by structure collapse and border effect, which could be improved by increasing its apparent material stiffness. This dynamic drop impact simulation process could be applied across numerous industries such as footwear, sporting goods, personal protective equipment, packaging, or biomechanical implants.

Lizard osteoderms – Morphological characterisation, biomimetic design and manufacturing based on three species

Osteoderms (OD) are mineralised dermal structures consisting mainly of calcium phosphate and collagen. The sheer diversity of OD morphologies and their distribution within the skin of lizards makes these reptiles an ideal group in which to study ODs. Nonetheless, our understanding of the structure, development, and function of lizard ODs remains limited. The specific aims of this study were: (1) to carry out a detailed morphological characterisation of ODs in three lizard species; (2) to design and manufacture biomimetic sheets of ODs corresponding to the OD arrangement in each species; and (3) to evaluate the impact resistance of the manufactured biomimetic sheets under a drop weight test. Skin samples of the anguimorphs H. suspectum and O. ventralis, and the skink C. zebrata were obtained from frozen lab specimens. Following a series of imaging and image characterisations, 3D biomimetic models of the ODs were developed. 3D models were then printed using additive manufacturing techniques and subjected to drop weight impact tests. The results suggest that a 3D printed compound of overlapping ODs as observed in Corucia can potentially offers a higher energy absorption by comparison with the overlapping ODs of Ophisaurus and the non-overlapping ODs of Heloderma. Compound overlapping ODs need to be further tested and explored as a biomimetic concept to increase the shock absorption capabilities of devices and structures.

Contemporary studies on suitability of biomaterials for mouth-guards

Use of Mouth Guards (MGs) can protect from such orofacial injuries in contact sports by reducing the impact force through its shock absorption capabilities. The objective of the current study is to organize relevant literature by other researchers following selection of suitable biomaterial for mouth guards. Orofacial injuries in contact sports (such as boxing, rugby, football, basketball, and karate, etc.) are common events. There are three different types of Mouth Guards available: Boil and bite, Stock, and Custom made. The Boil and bite are made by thermoplastic material and further heated in hot water and placing it in an athlete’s mouth by pressure application. The stock type has been found cheaper than the other two. The custom-made type is prepared on the imprints of the mouth of an individual patient. It has great benefits than two and provides greater comfort while speaking but slightly costlier. The MGs are available in different thicknesses according to the type of MGs and patient needs. Thickness carries an important role in fabricating MGs. Thickness affects comfort, breathing, speech, and shock absorption capabilities during activities. But there is still no specific thickness or material prescribed carrying good comfort and provides better protection from impact. It is still expected to conduct extensive impact studies on varieties of materials, combinations of available materials and also varieties of Biomaterials available for MGs to verify suitability being optimum one. EVA MGs, polycarbonate foam, polycarbonate-EVA Sandwich, polystyrene-polyolefin copolymer, new-generation polyolefin self-adapting MGs, Corflex have been seen to be the biomaterial choice for mouth guards.

Exogenous Shocks on the Dual-country Industrial Network: A Simulation Based on the Policies during the COVID-19 Pandemic

ABSTRACT This article investigates the performance of the industrial structure in different emerging markets under exogenous shocks during the COVID-19. Based on the ICIO database, we use System Dynamics to simulate the evaluation of the economic system under different types of exogenous shocks (instantaneous shocks like entertainment restrictions, and continuous shocks like trade controls). We find that there are significant differences in the shock absorption capability of a country, that capability is not related to the magnitude of the shock, but related to the type of shock and the industrial structure.

A Study on Shock Absorption Characteristics of Honeycomb-Inserted Bollards

Lack of shock absorption capability of conventional steel bollards causes significant vehicle damage and, consequently, high repair costs. This research studies a solution to reduce vehicle damage by inserting polylactic acid (PLA) honeycomb structures. A honeycomb-inserted bollard was designed based on numerical simulations using LS-DYNA, which yielded the bollard designed for actual vehicle-bollard collision experiments. Simulation efforts were focused on calculating the acceleration characteristics when a vehicle collides with steel and honeycomb-inserted bollards. Compared to the simulated steel bollards, 20 MPa yield-strength honeycomb-inserted bollard showed 0.017 s delay in the maximum acceleration occurrence time, reduction of the maximum acceleration of 37.4% of that of steel bollards, and a 13.1% reduction in the B-pillar maximum acceleration. Actual vehicle-bollard collision experiments, with a gyro-sensor installed at the test vehicle front bumper frame, also proved improved shock absorption characteristics of the honeycomb-inserted bollards. An experiment with honeycomb-inserted bollard showed a 0.783 s delay in the maximum acceleration occurrence time, a significant delay when compared to steel bollards. The maximum acceleration measured by the gyro-sensor was 0.35 × 103 m/s2 when the simulation predicted it to be 0.388 × 103 m/s2, proving the similarity in the simulations and experiments. Thus, this study of shock absorption characteristics promised reduced damage to vehicles and lower repair cost.

The influence of temperature on sheet lamination process when fabricating mouthguard on dental thermoforming machine.

Laminated custom-made mouthguards tend to delaminate with use; this is a problem in clinical use. Insufficient bonding strength causes delamination, and bonding strength is strongly affected by heating temperature during lamination. The present study aimed to evaluate the influence of heating temperature on the sheet lamination process. Seven mouthguard sheet products were laminated together at different heating temperatures. To evaluate the bonding strength, a delamination test (n = 6) was performed, and the fracture patterns were inspected visually. To evaluate the shock absorption capability, a falling impact test (n = 5) was performed, and the specimen thicknesses were measured. All recorded values were analyzed using two-way analysis of variance and Tukey's Honest Significant Difference Test (P < 0.05). The present study confirmed that bonding strength was dependent on heating temperature: In ethylene-vinyl acetate copolymer products, the bonding strength was almost constant at 130°C and above, and it was constant at 110°C and above in polyolefin products. The thickness of every specimen decreased and, in some specimens, the shock absorption capability decreased with increasing heating temperature. The present study concludes that the heating temperature during the sheet lamination process when laminated custom-made mouthguards are fabricated may not be less than 120°C in ethylene-vinyl acetate copolymer products and 110°C in polyolefin products.

Investigation of the mechanical performance of carbon/polypropylene 2D and 3D woven composites manufactured through multi-step impregnation processes

In this work, pre-impregnation techniques including Dr. Ernst Fehrer (DREF) spinning and electrostatic powder coating were used to negate the poor impregnation of highly viscous thermoplastics. The DREF spun hybrid yarns and electrostatic spray coated towpregs were woven into 2D and 3D fabrics and subsequently consolidated to yield two variations of 2D and four variations of 3D composites including 3D angle inter-lock and 3D orthogonal weave. The 2D composites possessed higher tensile and flexural strength than the 3D composites. However, better notch impact properties were observed for 3D orthogonal weave. The closer wrapping in 3D orthogonal slightly improves the shock absorption capability of the composite than the angle interlock composite. Composites made from powder coated towpregs performed better than composites made from DREF spun hybrid yarns, minimizing the effect of the weave pattern. Porosity was a common feature of composites manufactured from DREF spun yarns as observed from micro-CT images.

A Comparative Study of Shock Absorption Capacities of Custom Fabricated Mouthguards Using a Triangulation Sensor

This in-vitro study compares the shock absorption qualities of five mouthguard designs measured with a triangulation laser sensor during small hard object collisions. The aim was to investigate the impact of different labial designs on mouthguard performance. Methods: Five different custom-fabricated ethylene vinyl acetate (EVA) types of mouthguards with varying thickness and different labial inserts (polyethylene terephthalate glycol-modified (PETG), nylon mesh, air space) were tested with a triangulation laser sensor during different energy blows, generated with a pendulum testing device. The pendulum hits were applied to the center of a pivoted tooth crown in a custom-built upper jaw model. Measurements were executed with the mouthguards on the model and with no mouthguard as a negative control. Results: Tooth deflection was reduced with all mouthguards in comparison to no mouthguard. Increasing mouthguard thickness improved the mouthguards’ shock absorption capacities. Also, adding labial inserts increased their preventive qualities in ascending order: Mouthguard with a soft insert (nylon mesh), a hard insert (PETG), air space plus a hard insert (PETG). Conclusion: Increasing EVA foil thickness of a mouthguard, increasing labial thickness, and adding labial inserts (soft, stiff and air space) improve mouthguard shock absorption capabilities during small hard object collisions, thereby improving dental trauma prevention.

Modelling the cushioning properties of athletic tracks

In this work, a three-dimensional finite-element model of athletic tracks is presented. The model is based on data from quasi-static compression tests performed on small laboratory samples, to tune the constitutive parameters. The model was validated on three different athletic tracks, considering their top and bottom layers. Model predictions compared well with the results of shock absorption tests performed using a standard artificial athlete system, with relative errors of a few percent in terms of shock absorption. The model was then used to investigate the effect of the geometric structure of different tracks on their shock absorption capabilities. In particular, a reduction in size of the bottom layer cell pattern increased cushioning; the same property was shown to depend on the pattern voids depth in a non-monotonic way. A maximum in shock absorption was found for a void depth value about 40% higher than the one currently used in the analysed track patterns.

Design of a New Magnetorheological Damper Based on Passive Oleo-Pneumatic Landing Gear

In this research, a new type of magnetorheological (MR) damper, applicable to the landing gear system of airplanes, is presented. As a first step, an oleo-pneumatic damper, which is used for the landing gear system of small airplanes, is adopted. Its damping force is tested to determine the principal design parameters for the proposed MR damper. Thereafter, the structural configuration of the MR damper is characterized according to the operating principles of the adopted damper. The MR damper has two orifices and a recoil valve where one orifice is to be controlled by the flow direction. An analytical model for the field-dependent damping force is derived under both compressed and extended modes, followed by the analysis of the magnetic field intensity of the MR damper using the finite element method. After investigating the field-dependent damping characteristics, the dynamic equation for half of the airplane model is derived, and a simple, but effective, skyhook controller is formulated by considering the safety condition. Through computer simulations, it is shown that the proposed MR damper can provide the best vibration control and highest efficiency, which indicates the shock absorption capability of the damper during the landing stage.

Radial Inertia Effect on Dynamic Compressive Response of Polymeric Foam Materials

Polymeric foams have been extensively used in shock isolation applications because of their superior shock or impact energy absorption capability. However, as a type of soft condensed matter, the highly nonlinear, heterogeneous, and dissipative behavior of polymeric foams may result in an ineffective mitigation or isolation to shock/blast loading. To meet certain desired shock mitigation or isolation requirements, the polymeric foams need to be experimentally characterized to obtain their intrinsic material response. However, radial inertia during dynamic compression has become a severe issue and needs to be fully understood. In this study, we developed an analytical method to calculate the additional stress induced by radial inertia in a polymeric foam specimen. The radial inertia is generally caused by Poisson’s effect and associated with three different mechanisms – axial strain acceleration, large deformation, and Poisson’s ratio change. The effect of Poisson’s ratio change during deformation on radial inertia was specifically investigated for hyperelastic foam materials, and verified with experimental results obtained from Kolsky compression bar tests on a silicone foam.