Experimental evaluation of energy absorption and hysteresis in expanded polystyrene foams under repeated compressive loading

Traditional modeling of mechanical energy absorption due to compressive loadings in expanded polystyrene foams involves mathematical descriptions that are derived from stress/strain continuum mechanics models. Nevertheless, most of those models are either constrained using the strain as the only variable to work at large deformation regimes and usually neglect important parameters for energy absorption properties such as the material density or the rate of the applying load. This work presents a neural-network-based approach that produces models that are capable to map the compressive stress response and energy absorption parameters of an expanded polystyrene foam by considering its deformation, compressive loading rates, and different densities. The models are trained with ground-truth data obtained in compressive tests. Two methods to select neural network architectures are also presented, one of which is based on a Design of Experiments strategy. The results show that it is possible to obtain a single artificial neural networks model that can abstract stress and energy absorption solution spaces for the conditions studied in the material. Additionally, such a model is compared with a phenomenological model, and the results show than the neural network model outperforms it in terms of prediction capabilities, since errors around 2% of experimental data were obtained. In this sense, it is demonstrated that by following the presented approach is possible to obtain a model capable to reproduce compressive polystyrene foam stress/strain data, and consequently, to simulate its energy absorption parameters.

Expanded polystyrene (EPS) foam is a material, frequently used in a range of applications for its good energy absorption, thermal insulation, durability, and acoustic absorption. In this wide range of applications, the material undergoes a variety of loads that can extend from static to dynamic. When it comes to crush applications, these loading profiles create the need of well‐defined compression and tensile properties for a range of densities and strain rates. Herein, static and dynamic tension tests are conducted on EPS foam dog‐bone samples for material characterization. The target of the study is to obtain stress–strain curves for a range of densities spreading from 60 to 120 g L−1. For the low‐strain rates, tensile testing machines are used, whereas for the high‐strain rates, a modified drop tower set‐up is used. The influence of the strain rate on the stress–strain behavior, the dynamic strength, Young's modulus, and energy absorption capacities for different foam densities is measured. Furthermore, the experimental results for each density are compared with the predictions of Avalle's model for crushable foams to evaluate the validity of the model. The quality of fit obtained between experimental and theoretical is between 70% and 97% depending on the strain rate.

As an innovative technique, the lost foam casting (LFC) process has drawn great attention from both academia and industry in recent years. The key feature of LFC process is that a desired shape pattern made of expandable polystyrene (EPS) foam is buried in unbonded sand and replaced by advancing molten metal. The heat and mass transfer between the molten metal front and the EPS foam pattern plays an important role in the soundness of the product in the LFC process. The present study focuses on determining the characterization of heat and mass transfer during the EPS pattern degradation process. A unique experimental system using a cylindrical quartz window and heated steel block simulating the hot molten metal front has been constructed to make measurements and visualize the process. The foam pattern is 88 mm in diameter and 254 mm long. It is coated twice with DCH Ashland refractory material and the average coating thickness is 1.2 mm. The heat flux and pressure between the moving steel block and the EPS pattern are measured. The process variables studied during this experiment include foam density and steel block speed. It was found that unlike the fluidity of the molten metal which is highly dependent on the density of the foam patterns, foam density has marginal effect on the heat flux from the steel block to the foam pattern. The heat flux increases about 37% during a one-minute process under steel block velocity of 4.4 mm/s using different EPS foam density of 24 kg/m3 and 27 kg/m3. Flow visualization shows a gaseous gap formed between the steel block and the foam pattern. The phase change and degradation of EPS foam pattern and the heat and mass transfer in the gap are crucial to characterize the mold filling process which decides the quality of casting products. The maximum pressures measured in the gap using steel block velocity of 4.4 mm/s are 1.1 kPa and 1.4 kPa for EPS foam density of 24 kg/m3 and 27 kg/m3, respectively. Under a slower steel block velocity of 3.6 mm/s the gap peak pressure using 24 kg/m3 density EPS foam pattern is 0.43 kPa. It is concluded that higher foam density and faster steel block speed give rise to larger gas pressure between the steel block and foam pattern. The measured pressure values confirm data reported in literature.

Investigation into thermal characteristics of linear hotwire cutting system for variable lamination manufacturing (VLM) process by using expandable polystyrene foam

Mitigation of seasonal temperature change-induced problems with integral bridge abutments using EPS foam and geogrid

Dynamic crushing and energy absorption of foam filled multi-layer folded structures: Experimental and numerical study

A straightforward approach to recycle waste expanded polystyrene (EPS) foam to produce polystyrene (PS) microfibers using the improvised centrifugal spinning technique is demonstrated in this work. A typical benchtop centrifuge was improvised and used as a centrifugal spinning device. The obtained PS microfibers were characterized for their potential application for oil adsorption. Fourier transform infrared spectroscopy results revealed similarity on the transmission bands of EPS foam and PS microfibers suggesting the preservation of the EPS foam’s chemical composition after the centrifugal spinning process. Scanning electron microscopy displayed well-defined fibers with an average diameter of 3.14 ± 0.59 μm. At the same time, energy dispersive X-ray spectroscopy revealed the presence of carbon and oxygen as the primary components of the fibers. Contact angle (θCA) measurements showed the more enhanced hydrophobicity of the PS microfiber (θCA = 100.2 ± 1.3°) compared to the untreated EPS foam (θCA = 92.9 ± 3.5°). The PS microfiber also displayed better oleophilicity compared to EPS foam. Finally, the fabricated PS microfibers demonstrated promising potential for oil removal in water with a calculated sorption capacity value of about 15.5 g/g even at a very short contact time. The fabricated PS fiber from the waste EPS foam may provide valuable insights into the valorization of polymeric waste materials for environmental and other related applications.

Lightweight polypropylene/BaTiO3 composite foams with tunable dielectric constant

Expanded polystyrene (EPS) foams were flame retarded using ammonium polyphosphate (APP) and nano-zirconia (nano-ZrO2) by means of phenolic resin as a binder. It is found that the incorporation of a small amount (5 phr) of nano-ZrO2 into the APP flame-retarded EPS foams leads to 19% increase in flexural strength and 38% increase in compressive strength. Flame-retardant properties of the flame-retarded EPS foams were investigated by limiting oxygen index (LOI), UL-94 and cone calorimetry test (CCT). The LOI of the APP flame-retarded EPS foams in presence of nano-ZrO2 is above 31%, and the UL 94 V-0 rating can be reached. The CCT test results indicate that the APP flame-retarded EPS foams containing nano-ZrO2 have lower peak heat release rate, average effective heat of combustion and average specific extinction area. Moreover, thermal decomposition of the flame-retarded EPS foams was investigated by thermogravimetric analysis (TGA) and the TGA results illustrated clearly that the addition of nano-ZrO2 into the APP flame-retarded EPS foams leads to an increase in the residual char yield. The reason for the increase is possibly because ZrO2 may react during combustion process with pyrophosphoric acid produced from the thermal decomposition of APP to form zirconium pyrophosphate (ZrP2O7) confirmed by XRD studies of the char, which is helpful to improve the formation of the char. The XPS results showed that the ratio of oxidized carbons in the char increases with the presence of nano-ZrO2.

Quasi-static/dynamic energy absorption characteristics and micromechanical behavior of Al/Ep cast metal braided tubular structures

Influence of environmental factors on energy absorption degradation of polystyrene foam in protective helmets

Efficient energy absorption and dissipation are crucial for the development of novel protective materials under intensive dynamic loadings. Nanofluidic solid–liquid composite materials (NLCs) provide a promising pathway to engineer such materials owing to their rapid and reversible energy absorption and storage performance. In this study, we conducted systematic experiments on nanoporous SiO2 based NLCs to gain a better understanding of the dynamic mechanical behavior and the underlying energy absorption and storage mechanisms under compressions with varying strain rates. Our findings indicate that the energy absorption in terms of dissipation and storage under the repeat compressive loadings includes two stages. The initial stage indicates the maximum energy absorption capacity, which is efficiently improved by the adding electrolyte solution and the retreatment. The stable energy absorbing stage represents the reversible energy absorption and storage capacity of the NLCs. Based on the noticeable strain rate effect, a three-stage mechanism is proposed to explain the significant increase of energy absorption capacity with the varying compressive strain rates. The superior reusable energy absorption capacity of NLCs holds great promise for their use as excellent energy-absorbing materials under intensive impulsive loadings.

Investigation of novel expandable polystyrene/alumina aerogel composite thermal insulation material

New composite liners for energy absorption purposes

In frontal impacts, the usage of thin-walled box structures in the front-end of vehicles is crucial for effectively absorbing collision energy. However, achieving maximum energy absorption while considering constraints such as available space, weight, cost, and maintaining occupant safety is a challenging task. Previous studies have indicated that the structural shape, utilization of high strength materials, and incorporating foam-filled structures can significantly enhance energy absorption capacity. This paper presents a novel approach to optimize the energy absorption capacity with a combination of conventional and auxetic materials. Auxetic materials possess a unique characteristic of exhibiting a negative Poisson’s ratio, which means they contract when compressed and expand when subjected to tension. These distinctive properties enable auxetic structures to achieve higher stiffness and improved impact resistance while remaining lightweight. In this paper, a Finite Element Analysis (FEA) methodology has been formulated with a simple crush box, and with multiple materials combinations of conventional materials such as high strength steels, Aluminum and auxetic materials, to improve the energy absorption capacity. The significant factors affecting the energy absorption which are critical to occupant safety have been compared between the simulations. It is demonstrated that the optimal blend of conventional materials such as Aluminum and Ultra High Strength Steels, when integrated with auxetic structures, exhibits a higher potential for maximizing the specific energy absorption capacity of these structures. The findings reveal that the optimized combination of the above-mentioned materials can increase the specific energy absorption (SEA) capacity by up to 256%. Additionally, the practical application of these findings is demonstrated through full vehicle level crash analyses aimed at achieving light weighting. The research findings were implemented on the Ford Taurus FE model, available online and validated experimentally that shows benefits of 7.83kg weight reduction for the same crash performance of a standard material taken as baseline.