The impact speed was 1.22 m/s and 1.4 m/s, respectively. Khosroshahi S.F., Olsson R., Wysocki M., Zaccariotto M., Galvanetto U. Dynamic mechanical properties of closed cell aluminum foam under medium and low strain rates. Firsttechnique is known as Open Cell manufacturing while the other is called Closedcell manufacturing. Consequently, the stressstrain curve is shown in Figure 7b, and its strain rate was calculated over the proportional region of the specimen displacementtime relationship. Zheng Z.J., Yu J.L., Li J.R. Rc represents the compressed part. Zheng Z., Liu Y., Yu J., Reid S.R. Tan P.J., Harrigan J.J., Reid S.R. Kesavan A., Madhavan V.R.B., Chinnadurai E. Mechanical and thermal properties of PVC and polyurethane foam hybrid composites. Nine specimens were tested under the quasi-static test (QSST), which were divided into three groups. According to reference [42], 0, L, and E1 can be obtained from the stressstrain curves. The specimen deformation becomes progressively more localized as the compressive strain rate is increased and the deformation mode changes from homogeneous to transitional to shock mode, as shown in Figure 1 [41]. Dynamic crushing of cellular materials: Continuum-based wave models for the transitional and shock modes. Hence, local microstructure variations in the foam affect the foam compression response observed in Figure 7b. FOIA In some foams, there is a wide range of stomatal sizes and stomatal wall thicknesses. The specimen energy absorption varied linearly in the early stage and then increased rapidly, corresponding to a uniform compression process. Such an effect combines the elastic, plateau, and densification effects in a small zone and does not lead to the appearance of individual zones in the energy density curve for the entire specimen. The stressstrain curve of the foam at an intermediate strain rate was obtained. The craft, however, will encounter unexpected loads, such as bird strikes or other objects. The gas, pockets make foam very light weight and at the time of impact most of the, energy is absorbed by the material and hence it helps in minimising the damage. The testing results in the shock tube test: (a) the diagram of the velocity of the compression deformation as a function of the time, here, the blue line represents the experiment velocity and the red line represents the idealized velocity, and the average velocity of the compression is about 155 m/s; (b) the typical corresponding pressuretime curve of the shock tube, here, the blue line represents the pressure recorded by sensor 1 and the red line represents the pressure recorded by sensor 2, ps represents the first reflected wave, and p5 represents the second reflection wave; (c) the dynamic crushing stress A as a function of the specimen compression ratio in the shock tube experiment, which was calculated by Equation (6). Youssef G., Reed N., Huynh N.U., Rosenow B., Manlulu K. Experimentally-validated predictions of impact response of polyurea foams using viscoelasticity based on bulk properties. The result is a smooth plateau with slow deformation. Tang N.H., Lei D., Huang D.W., Xiao R. Mechanical performance of polystyrene foam (EPS): Experimental and numerical analysis. A new method for obtaining the stressstrain curve of foams under intermediate strain rate deformation is provided by modifying a drop weight test machine. In the absence of complete fracture, there may be vibrations in the specimen and multiple impacts due to rebound (although air brakes and other methods can be used to minimize such effects). The dynamic crushing stress A can be calculated by Equation (6), where 0 can be obtained from the quasi-static tests and Vs can be obtained from Figure 8a. Zhang H., Zhou Y., Zhang F., Gong W., He L. Studies on Foaming Properties and Mechanical Properties of Polypropylene /beta-Cyclodextrin Foamed Composite. Overall, the damage is nonuniform in the specimen along the length. Therefore, we cannot get the strainstress curve. The deformation at an intermediate strain rate is not expected to be uniform along the specimen length. The final total compression energy density of the specimen in quasi-static and intermediate strain rate reaches 0.1 MJ/m3 and 0.17 MJ/m3, respectively. The observations of drop weight impact in Figure 10a show that the center of the specimen has deformed preferentially, not the top part close to the impact. Aluminium metalfoam is used in many sectors like : +7 (343) 344 44 11 info@alupor.com, Simple experiment shows low deflection of impact with ALUPOR. Miltz J., Ramon O. Therefore, the forcetime curve can be converted to obtain the stressstrain curve of the specimen, as shown in Figure 6b. Both the diameter and height of the specimens are 25.4 mm. The intermediate strain rate for this experiment was in the range of 40 s1. Moreover, the energy density trend under the shock loading condition was different. When the impact stress of A inside the specimen is greater than the compaction stress of the specimen (L), the shock mode appears [41,42,43,44]: where Vs is the compression velocity of the foam, L is the densification strain of the foam. In order to study the energy absorption characteristics of polymer foam under high strain loading, a new method to obtain the energy absorption was found through theoretical derivation. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (. The mechanical response characteristics of the foam in intermediate experiments under a strain rate of 40 s1: (a) drop tower test curve corresponding to the displacement, force, and time of the experiment, the orange line represents the force of the specimen, and the blue line represents the compression displacement of the specimen; (b) the strainstress curve of the foam in the drop tower experiments, here, the yield stress is 0.0109 MPa. Using a shock tube as a controlled experimental platform is very helpful for determining the high strain rate properties of materials. Here, the test theory is presented, and the test platform is designed with a special foam fixture and a visualization of the end of the tube, which is able to test foam impact properties and monitor the foam failure progress. The trends of energy density under high strain rate deformation in previous studies are similar to the results obtained in this test, as the energy density changed linearly with the increase in strain rate [54,55]. An official website of the United States government. The results from impact tests are augmented with high strain rate loading results obtained from a shock tube-based test method [35,36,37]. Between 1750 and 1850, a new kind of revolution startedfrom England which was later knows as Industrial Revolution by thehistorians. El-Qoubaa Z., Othman R. Strain rate sensitivity of polyetheretherketones compressive yield stress at low and high temperatures. The shock wave has a high temperature, which caused this phenomenon. The Poissons ratio of the material was found to range from 0.15 to 0.78. However, as the core of sandwich composites, the energy absorption of foam is still unclear. The new PMC design is here! Johnsen J., Grytten F., Hopperstad O.S., Clausen A.H. It can be seen from the picturesthat the overall deformation of the specimen is not uniform from the beginning of the test. When the specimen is opened, it can be seen that the changes in internal and external appearance are consistent. The average diameter of the cells and the wall thickness were 1.49 mm and about 0.017 mm, respectively. Pei L., Guo Y.B., Zhou M.W., Shim V.P.W. An in-house Matlab code was developed to process the high-speed camera images to measure specimen deformation. Krundaeva A., De Bruyne G., Gagliardi F., Van Paepegem W. Dynamic compressive strength and crushing properties of expanded polystyrene foam for different strain rates and different temperatures. Writingoriginal draft, formal analysis, B.Y. Although the quasi-static (103 s1) and intermediate (40 s1) tests were conducted at four orders of magnitude of strain rate, the failure features of specimens are similar, which show that some plastic deformation is not recovered and densified cells scattered in the specimen. An Experimental and Computational Study of the High-Velocity Impact of Low-Density Aluminum Foam. Shock tubes, having a single or a double diaphragm fracture mechanism to generate shock waves, have been widely used in aerodynamics research [38,39]. Viscoelastic behavior of polymeric foams: Experiments and modeling. Deformation response of EPS foam under combined compression-shear loading. According to [41], the impact energy can be divided into deformation energy and other energy loss, and can be given by: where Es and Ew are the energy absorption of foam under the high strain rate loading and the other energy loss, respectively. In addition, the results obtained from this kind of impact cannot be compared to those obtained from compression tests due to the difference in the specimen loading configuration. This work used a modified drop weight impact tower to conduct the testing of polyethylene (PE) foam at intermediate strain rate compression. SHPB experiment research on dynamic property of expanded polystyrene foam. The pressure curve was obtained by the two pressure sensors mounted in the shock tube. The results showed that the foam exhibited a nonuniform deformation along the specimen length under high strain rates. A representative set of specimens failed under quasi-static, intermediate, and high strain rate compression are shown in Figure 9ac, respectively. The signal of the load cell was amplified and transmitted to an oscilloscope (Tektronix TDS 2014B, Tektronix, Inc., Beaverton, OR, USA) before being captured by a computer. Alpher R.A., White D.R. However, the shock tested (greater than 6100 s1) partially melts and resolidifies the specimen surface during the high strain rate deformation. Based on the test method, the failure progress and final failure modes of PE foams are discussed and, moreover, energy absorption capabilities of PE foams are assessed under both quasi-static and high strain rate loading conditions in this paper. All authors have read and agreed to the published version of the manuscript. Federal government websites often end in .gov or .mil. The impact test of foam with high strain rate loading was also explored. In the process of rapid deformation, there is not enough time to redistribute the stress, which causes a significant vibration phenomenon. The mechanical response characteristics of foam materials in quasi-static experiments under a strain rate of 103 s1: (a) The diagram of the force and the displacement of foam materials as a function of the time, r1 is the linear phase, r2 is the plateau phase, and r3 is the density phase, the orange line represents the force of the specimen, and the blue line represents the compression displacement of the specimen. The loading speed exhibited an obvious influence on energy density. This is also a key factor in the foams ability to absorb energy. The magnitude of the vibration is determined by the number of stomatal units that collapse due to this initial cascade effect. Energy absorption characteristics of polymeric foams used as cushioning materials. The third group of tests were conducted at high strain rates using a double diaphragm aerodynamic shock tube. Foamis substance obtained as a result of trapping gas in liquid or solid. Dynamic compressive behavior of rigid polyurethane foam with various densities under different temperatures. will also be available for a limited time. According to the rigidplasticlocking (R-P-P-L) model, the dynamic crushing stress A at the proximal end is derived as [43,48,49,50]: The foam energy absorption is calculated by: The impact energy of the incident wave in the shock tube can be calculated by [51]: where Ei is the impact energy of the incident wave. Guo Y., Yang H., Liu X., He S., Wang J. Licensee MDPI, Basel, Switzerland. Dynamic crushing of honeycombs and features of shock fronts. Tan P.J., Reid S.R., Harrigan J.J., Zou Z., Li S. Dynamic compressive strength properties of aluminium foams. (a) Homogeneous mode: the stress values on the proximal and distal surfaces of the specimen are equal and the strain is distributed uniformly along the specimen length. The experimental results showed that the stress of the material increases with the increase in strain rate. The specimen front takes a concave shape, likely similar to the shape of the shock front at 0.12 ms and then it reverses to a convex shape at 0.15 when the shock reflects from the back part. However, since the loading time and loading strain displacement of the split Hopkinson pressure bar have certain limitations, the condition of high strain rate loading for closed cell polymer foam of large thickness cannot be achieved. Yang B., Cao Z., Chang Z., Zheng G. The effect of the reflected shock wave on the foam material. Inertia effects in uniaxial dynamic compression of a closed cell aluminium alloy foam. The site is secure. all are the result ofadvancements made in technology after Industrial Revolution. The Aluminium metal foam has vast range of applications. A transparent specimen chamber is constructed to allow for capturing the specimen deformation using a high-speed camera. The cells inside were twisted, and many of the cells had a flat shape. In the drop weight experiment, the compressive force and the specimen length were simultaneously measured and are plotted over time in Figure 7a. Ramirez B.J., Misra U., Gupta V. Viscoelastic foam-filled lattice for high energy absorption. In order to improve the impact resistance of aircraft, it is of great significance to study the energy absorption characteristics of polymer foam material. However, because of factors such as the cellular structure and viscoelastic nature of the polymer, the evaluation of elevated strain rate properties of foams is challenging [20,21,22]. Ha N.S., Lu G.X., Xiang X.M. These observations show that the specimen failure behavior transitions from uniform to nonuniform compression and the transition zone is greater than the strain rate of 40 s1 tested in this work. The impact energies were 4 J and 3 J, respectively. The pressure of the incident shock front is denoted as p2 and recorded by two pressure sensors. The present work involved a modified drop weight impact instrumentation, where a standard hemispherical impact tup was replaced with a 25 mm diameter flat face tup to load a cylindrical specimen of the same diameter. Li Z.J., Chen W.S., Hao H. Mechanical properties of carbon foams under quasi-static and dynamic loading. The strain rates of these QSSTs were set at 103 s1, 102 s1, and 101 s1. Five specimens were tested, and their deformation was also captured by the high-speed camera with a frame rate at 100,000 Hz. The energy absorption characteristics of PE foam under the impact were analyzed and are discussed. Zhang J.X., Qin Q.H., Chen S.J., Yang Y., Ye Y., Xiang C.P., Wang T.J. Low-velocity impact of multilayer sandwich beams with metal foam cores: Analytical, experimental, and numerical investigations. Reid S.R., Peng C. Dynamic uniaxial crushing of wood. Diagram of the stress of foam materials as a function of the strain , the green line is R-P-P-L model and the red line is R-LHP-L model [42]. Influence of strain rate and temperature on the mechanical behaviour of rubber-modified polypropylene and cross-linked polyethylene. Effect of microstructure on the properties of polystyrene microporous foaming material. The rigidlinearly hardening plasticlocking (R-LHP-L) model is adopted to judge the three modes [42]. The gaspockets make foam very light weight and at the time of impact most of theenergy is absorbed by the material and hence it helps in minimising the damageof impact. Duan Y., Zhao X.H., Du B., Shi X.P., Zhao H., Hou B., Li Y.L. Le Barbenchon L., Kopp J.B., Girardot J., Viot P. Reinforcement of cellular materials with short fibres: Application to a bio-based cork multi-scale foam. Here, both a modified drop weight impact method and the shock tube test method were used for foam shock testing at high strain rates. Hwang B.K., Kim S.K., Kim J.H., Kim J.D., Lee J.M. ; Writingreview & editing, validation, Y.Z. It can be argued that this figure does not present the stressstrain curve for the specimen, because that the specimen deformation behavior at such a high strain rate is not uniform and the strain is preferentially localized close to the specimen front surface. Closed-cell polyethylene (PE) foam (Pregis, Aurora, IL, USA) with a density of 27.2 kg/m3 was selected, as shown in Figure 3. The density is 27.2 kg/m3, the average diameter and the wall thickness of the cell are 1.49 mm and about 0.017 mm, respectively. In the shock mode, the stress in the specimen is not uniform. Modeling the elastic response of polymer foams at finite deformations. Flexural deformation behavior of carbon fiber reinforced aluminium hybrid foam sandwich structure. The difference in PE foam material behavior in homogeneous mode and shock mode was observed through experiments. 
The high-speed camera images, shown in Figure 10, also provide further evidence. It is found that the tup velocity did not reach the condition of transition mode, while the velocity of shock wave reached the condition of shock mode. The intermediate strain rate compression tests were conducted on a modified Dynatup 9200 series drop weight impact tower, as shown in Figure 4b. The test was conducted at a strain rate of 103 s1 calculated from Figure 6a, allowing uniform compression of the foam specimen, as the length L of the specimen and the strain rate of the compression specimen were known. Ld is the distance between two pressure sensors, and Lb is the distance between the second sensor and rigid plate. foam, high strain rate, energy absorption, failure. Xu P.B., Yu Y., Li K., Wu X.T. Later two patents of sponge-like metal were given to Benjamin Sosnik in1948 and 1951 for applying mercury vapour to blow liquid aluminium and creating the firstaluminium metal foam. In this figure, the specimen length steadily decreased at a constant rate while the compressive load increased moderately, and its rate turned to zero at the moment the compressive load reached the maximum value. An experimental and numerical survey into the potential of hybrid foams. However, in fact, the internal stress of the specimen was not uniform (this phenomenon will be shown in the next section), so it can be judged that the strain rate of the specimen was greater than 6100 s1, which is a high strain rate deformation. Response of a helmet liner under biaxial loading. Basicallythere are two methods of manufacturing the aluminium metal foam. The world we live in is the result of that revolution, the massproduction of commodities, heavy machinery, etc. The commercial production of aluminium metal foam beganin 1990s in Japan. If the internal strain of the specimen is assumed to be uniform during the compression process, the strain rate of the specimen should be 6100 s1. The https:// ensures that you are connecting to the In homogeneous mode, the energy absorption of foam under plastic deformation can be calculated according to the stressstrain curve under quasi-static loading [45,46,47]: where Eq is the energy absorption of foam under quasi-static loading, L is the strain entering the densification phase, is the stress of the foam, D is the volume of the specimen. The stresscompression ratio curve of the specimen front during the whole compression is presented in Figure 8c. The typical deformation progress of the foam in drop weight impact test and shock tube test: (a) drop weight impact test; (b) shock tube experiment. Response of anisotropic polyurethane foam to compression at different loading angles and strain rates. In addition, research on foam core sandwich composites will also be carried out by combining the foam material with a skin in further work. Avalle M., Belingardi G., Montanini R. Characterization of polymeric structural foams under compressive impact loading by means of energy-absorption diagram. Energy-absorbing characteristics of foamed polymers. The energy density is greatly affected by velocity under the shock mode. This demonstrates that the energy density value is greatly affected by velocity under the shock mode. The deformation and the strain of the foam were studied by a high-speed camera and, moreover, the energy absorption of the foam under different loading rates is discussed. Industrial Revolution not only increased the rate of production but the rate ofaccidents and injuries while working were also greatly increased. It can maximize its energy absorption characteristics and maintain stable energy absorption capacity under a high-speed impact. Three deformation modes of foam material under different loading rates [41]. This incident shock wave traveled through the driven chamber and interacted with the specimen placed in a transparent acrylic test chamber. The main reason of most of the injuries is impact. When the speed is less than 1.3 m/s, this stable energy absorption state disappears. The pressures behind the shock wave, p2, ps, and p5, all maintain a stable pressure value (see Figure 8b). Bosi F., Pellegrino S. Nonlinear thermomechanical response and constitutive modeling of viscoelastic polyethylene membranes. Miralbes R., Ranz D., Ivens J., Gomez J.A. Hohe J., Beckmann C., Bohme W., Weise J., Reinfried M., Luthardt F., Rapp F., Diemert J. A split Hopkinson pressure bar is the most popular experimental method in the study of metal high strain loading. Zhang Y., Jin T., Li S., Ruan D., Wang Z., Lu G. Sample size effect on the mechanical behavior of aluminum foam. Koohbor B., Ravindran S., Kidane A. Thematerial which was introduced for this purpose was later known as foam. The images at 0.12 and 0.15 ms show a very interesting fact. 8600 Rockville Pike Metal foam was first seen in 1926 by Meller in a Frenchpatent. This convex shape of the specimen is also visible in Figure 10b for the shock loaded specimen, while the quasi-static and intermediate strain rate tested specimens show a flat front. Effects of cell-wall instability and local failure on the response of closed-cell polymeric foams subjected to dynamic loading. However, the standard test methods have some limitations in characterizing foams due to their large elastic strain, viscoelastic material characteristics, and high damage tolerance and the methods need to evolve for such materials [23,24,25]. Henriques I.R., Rouleau L., Castello D.A., Borges L.A., Deu J.F. Shock tests resulted in strain rates of 6.1 10. The strain rates of these drop weight tests were set at 40 s1 and 36 s1, respectively. The representative shock test results of foam specimens are presented in Figure 8. The data presented in this study are available on request from the corresponding author. The images at 0.04 and 0.08 ms show that the front part of the specimen was much more severely deformed than the back part. When the specimen is completely compressed and hits the rigid body, a second reflection wave (p5) is generated. The increment of injuries and accidents gave birth to anew sector which was later know as Healthand Safety Sector which was related to health and safety of individuals. It can be seen from the references that the energy density curves obtained are the same as those obtained in [52,53]. 
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