Abstract

Most running shoe midsoles are made of ethylene vinyl acetate (EVA) foam although excellent mechanical long-term properties of polyurethane (PU) foam are generally known. The aim of this study was to investigate whether PU foam is applicable as midsole material regarding damping properties. Short-term and long-term mechanical tests were conducted for running shoes with midsoles of either PU or EVA foam using the Hydraulic Impact Test. The results of the short-term testing show that PU midsoles can be adjusted to a wide range of damping properties while EVA midsoles attained good average values. In long-term testing, however, the EVA foams exhibited higher relative changes of damping parameters than the PU materials, which confirms the durability and ageing resistance of PU.
c
2010 Published by Elsevier Ltd.
Procedia Engineering 2 (2010) 2789–2793
www.elsevier.com/locate/procedia
1877-7058 c
2010 Published by Elsevier Ltd.
doi:10.1016/j.proeng.2010.04.067
2790 K. Br¨
uckner et al. / Procedia Engineering 2 (2010) 2789–2793
K. Br¨
uckner et al. / Procedia Engineering 2 (2010) 2789–2793 2791
2792 K. Br¨
uckner et al. / Procedia Engineering 2 (2010) 2789–2793
K. Br¨
uckner et al. / Procedia Engineering 2 (2010) 2789–2793 2793
... That study used whole shoes (size 8.5 US) but only the heel was subject to impact. Measured under a variety of testing methods and shoe types, midsole stiffness was found to be between 30-439 N/ mm 38,[43][44][45] . These studies suggest that lower stiffness midsoles provide better cushioning (i.e. more energy stored) but experience high impact forces because the foot is not slowed down fast enough. ...
... larger area under the force-displacement curve). Furthermore, the stiffness of most velar bone mimics were within the range of previously measured midsole stiffnesses (30-429 N/ mm 38,[43][44][45]. These values include previous studies that tested midsoles from different manufacturers, different test geometries (whole shoe or midsole section), different materials (PU, EVA, or EPS), and with different mechanical testing procedures (displacement versus load-controlled compression). ...
... These values include previous studies that tested midsoles from different manufacturers, different test geometries (whole shoe or midsole section), different materials (PU, EVA, or EPS), and with different mechanical testing procedures (displacement versus load-controlled compression). For energy storage, our results are in the range of previously published values for energy storage of midsole foams during quasi-static compression (960-1680 mJ) 38 . However, for dynamic impact testing the energy storage and specific energy storage of the velar bone mimics is inferior to that of the EVA foams. ...
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Rocky Mountain bighorn sheep rams (Ovis canadensis canadensis) routinely conduct intraspecific combat where high energy cranial impacts are experienced. Previous studies have estimated cranial impact forces to be up to 3400 N during ramming, and prior finite element modeling studies showed the bony horncore stores 3 × more strain energy than the horn during impact. In the current study, the architecture of the porous bone within the horncore was quantified, mimicked, analyzed by finite element modeling, fabricated via additive manufacturing, and mechanically tested to determine the suitability of the novel bioinspired material architecture for use in running shoe midsoles. The iterative biomimicking design approach was able to tailor the mechanical behavior of the porous bone mimics. The approach produced 3D printed mimics that performed similarly to ethylene–vinyl acetate shoe materials in quasi-static loading. Furthermore, a quadratic relationship was discovered between impact force and stiffness in the porous bone mimics, which indicates a range of stiffness values that prevents impact force from becoming excessively high. These findings have implications for the design of novel bioinspired material architectures for minimizing impact force.
... From the existing research, EVA midsole material represents the lighter weight and excellent energy return ability, optimizing performance while helping prevent injuries [22,50]. What is more, the blends of EVA and other polymer materials, such as PHYLON, also known as secondary foaming materials, are more effective than EVA materials in damping performance, elasticity, and durability. ...
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Although various sports footwear demonstrated marked changes in running biomechanical variables, few studies have yielded definitive findings on the underlying mechanisms of shoe constructions affecting running-related performance and injuries. Therefore, this study focused on examining the effect of basic shoe constructions on running biomechanics and assessing the current state of sports shoe production in terms of injury and efficiency. Relevant literature was searched on five databases using Boolean logic operation and then screened by eligibility criteria. A total of 1260 related articles were retrieved in this review, and 41 articles that met the requirements were finally included, mainly covering the influence of midsole, longitudinal bending stiffness, heel-toe drop, shoe mass, heel flare, and heel stabilizer on running-related performance and injuries. The results of this review study were: (1) The functional positioning of running shoe design and the target groups tend to influence running performance and injury risk; (2) Thickness of 15–20 mm, hardness of Asker C50-C55 of the midsole, the design of the medial or lateral heel flares of 15°, the curved carbon plate, and the 3D printed heel cup may be beneficial to optimize performance and reduce running-related injuries; (3) The update of research and development concepts in sports biomechanics may further contribute to the development of running shoes; (4) Footwear design and optimization should also consider the influences of runners’ strike patterns.
... Today, the industrial use of polymeric foams is expanding due to their low density and weight, as well as their outstanding thermal and acoustic insulation, impact damping and energy absorption properties [1][2][3][4]. The leading industries are increasingly using foams, and the global polymer foam market is continuously growing. ...
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This study examines the effect of foam thickness on impact damping properties of closed‐cell cross‐linked polyethylene foams of different densities. Compression tests and falling weight impact tests were performed to detect the most important mechanisms, which affect the mechanical properties of the foams. The results showed that impact damping properties are significantly influenced by foam thickness, while energy‐absorbing capability primarily depends on foam density. The average cell diameter was determined with a scanning electron microscope, which proved that the mechanical properties are mostly influenced by cell structure because higher density foams have smaller cells and thicker cell walls. Other important conclusion is that a foam thickness limit can be determined for a given load level to avoid excessive compaction of the cells and maximize the shock absorption of the foam. Polymer foams are widely used in the industry due to their outstanding energy‐absorption. In this study, several falling weight impact tests were conducted on different density cross‐linked polyethylene foams to analyze the effect of foam thickness. The results showed that impact damping capability is significantly influenced by thickness, as in thinner foams, the cells are fully compacted during the collision. This compaction causes irreversible damages in the cell structure and deterioration in the mechanical properties.
... So ist sie zum Beispiel für die Ausprägung der funktionellen Sportschuhparameter Dämpfung, Stabilität, Torsionsfähigkeit, Vorfußflexibilität, Abrollverhalten und Schuhgewicht verantwortlich. Die noch immer am häufigsten verwendeten Werkstoffe sind PUR (Poly urethan) und insbesondere EVA, wobei PUR zwar langlebigere Nachgiebigkeitseigenschaften aufweist, jedoch schwerer als EVA ist [26]. Größ -"one piece mold/grind": Bei dieser Konstruktion werden die Blocker zuerst "vorgeformt" ("premolded") und dann zugeschliffen. ...
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Plantar pressure induced pain leads to discomfort and hinders the activities of daily living. Various custom orthoses are fabricated for this ailment. However, there is a lack of science or material innovation on such orthoses for reducing the plantar pressures, and the validation of the same. The objective of the study was to fabricate a novel foot orthosis with multiple materials for effective plantar pressure reduction. The methodology included 3D scanning and 3D printing of a full-scale foot, and employed materials of different densities like polyurethane, EVA, plastazote, and biomimetic silicone polymer for the custom orthosis fabrication. This device was tested on a healthy subject for validation using a pressure mapping device. A significant reduction of plantar pressures was observed at the forefoot and heel regions, up to 65%. The plantar pressures at the mid foot regions were retained, indicating adequate arch support provided by the custom orthosis. With further testing, the developed orthosis can be one of the first lines of prescription for patients with plantar pain.
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Book
Improvements in materials technology have made a significant impact on sporting performance in recent years. Advanced materials and novel processing methods have enabled the development of new types of equipment with enhanced properties, as well as improving the overall design of sporting goods. The interdependence between material technology and design, and its impact on many of the most popular sports, is reviewed in this book. Materials in sports equipment presents the latest research, from a distinguished panel of international contributors, into the chemical structure and composition, microstructure and material processing of the various materials used in a wide range of sports. The relationship between performance and design is examined in detail for each sport covered. Part one concentrates on the general use of materials in sports. Here, the reader is given a broad insight into the overall influence of materials in sports, and the significance of material processing and design. Part two focuses on showing how individual sports have benefited from recent improvements in material technology. It also analyses the way in which improvements in our understanding of biomechanics and the engineering aspects of sports equipment performance have influenced materials and design. Sports whose equipment is considered in detail include: golf, tennis, cycling, mountaineering, skiing, cricket and paralympic sports. The overall aim of the book is to make the reader aware of the interaction between the type of material, its selection, processing and surface treatment, and show how this process underpins the performance of the final sporting product. It is essential reading for all materials scientists and researchers working in this rapidly developing field.
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The mechanical characteristics of foamed plastics, based on commercial foams, were studied by observing the role of cell content (foam and relative densities, dimensions of cell edge and face, cell wall, cell shape, etc.) on stress-strain behavior and deformation mechanisms. It is found that the stress-strain behaviour in compression and tension for PVC commercial foam are different beyond linear elastic deformation since cell wall deformations involve different processes. Cell wall thickness which is directly related to foam density dominates the mechanical properties of plastic foams. The regimes of the stress-strain curve are related to the structure of the foam. The foam deformation structure was identified by SEM micrographs which assisted in the interpretation of deformation mechanisms. The mechanical properties of these plastic foams were also characterized in terms of relative density and the degree to which the cells are open or closed. It is found that relative density was found to be a function of geometric aspects of cell structure such as edge and face connectivity, edge and face thickness, etc, which are critical to the understanding of the mechanical properties.
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Eine der Möglichkeiten, die Belastung am menschlichen Bewegungsapparat zu beeinflussen und zu reduzieren, ist der Sportschuh. Am Beispiel des Laufschuhs kann aufgezeigt werden, wie Strategien gewählt werden können, um dieses Ziel zu erreichen. Drei Aspekte sind wichtig beim Laufschuh, Dämpfen, Stützen und Führen. Um eine ideale Dämpfung zu erzielen ist weniger das Material der Zwischensohle, als vielmehr die Geometrie der Schuhsohle und des gesamten Schuhs zu berücksichtigen. Ein analoger Kommentar kann für das Stützen gemacht werden. Eine geometrische Veränderung der Fersenpartie des Schuhs in Richtung der menschlichen Ferse verkleinert die Pronationsbewegung. Laterale Stützen im Vorfuß ermöglichen eine Kontrolle der Abstoßbewegung (Führen). Ein konsequentes Anwenden dieser Überlegungen sollte eine Verminderung der Belastung des Bewegungsapparates beim Laufen bewirken und damit als präventive Maßnahme gegen Überlastungserscheinungen wirken.
Chapter
In this report a test setup is presented that has been developed to generate a life cycle stress to the heel part of running shoes. The force-time-relationship has been derived from biomechanical investigations on ground reaction forces during running. By having investigated a range of 13 shoes it could be demonstrated that mechanical degradation leads to significant changes in the ability of sole materials to absorb energy. Furthermore an increased stiffness can be shown. KeywordsDurability-Mechanical Testing-Running shoes
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One possible means of influencing and reducing the load on the human locomotive apparatus is the running shoe. Taking this as an example it can be shown how strategies for achieving this goal can be selected. The running shoe has three important characteristics: cushioning, support, and guidance. To achieve ideal cushioning, it is important to consider not so much the material of the inner sole, but rather the geometry of the shoe sole and the entire shoe. An analogous commentary may be made as regards support. By modifying the heel part of the shoe to approximate the human heel, pronation movement can be reduced. Lateral supports in the forefoot make it possible to control the propulsive movement (guidance). Consistent application of these considerations should bring about a reduction in the load on the locomotor apparatus and thus help prevent overstrain phenomena.
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The change in shock absorption properties of running shoes was evaluated as a function of miles run. Differ ent models of running shoes encompassing a wide range in retail price were obtained and mechanically tested to simulate the repeated heel strikes of running. The energy absorbed by the shoes was determined from the area under the load deformation curve at the equivalent of 0, 5, 10, 25, 50, 75, 100, 125, 150, 200, 250, 300, and 500 miles of running. Shoes were also tested at similar intervals after having been worn by volunteers during normal training. An approximate 33% difference in the initial shock absorption was observed in the different shoe models. In general, the shoes retained approximately 75% of their initial shock absorption capability after 50 miles of simulated running, and approximately 67% after 100 to 150 miles. Between 250 and 500 miles the shoes retained less than 60% of their initial shock absorption capacity. No differences in shock absorption character istics were apparent based upon either shoe price or the manufacturer model. The results of shoes tested by the volunteer runners also showed a marked reduc tion in shock absorption with mileage. The loss, how ever, was not as great as in the machine-simulated running, with approximately 70% of initial shock ab sorption retained at 500 miles.
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A finite element analysis (FEA) was made of the stress distribution in the heelpad and a running shoe midsole, using heelpad properties deduced from published force-deflection data, and measured foam properties. The heelpad has a lower initial shear modulus than the foam (100 vs. 1050 kPa), but a higher bulk modulus. The heelpad is more non-linear, with a higher Ogden strain energy function exponent than the foam (30 vs. 4). Measurements of plantar pressure distribution in running shoes confirmed the FEA. The peak plantar pressure increased on average by 100% after 500 km run. Scanning electron microscopy shows that structural damage (wrinkling of faces and some holes) occurred in the foam after 750 km run. Fatigue of the foam reduces heelstrike cushioning, and is a possible cause of running injuries.
Handbook of polymeric foam and foam technology
  • D Klempner
  • V. Sendijarevic
  • D Klempner
  • V. Sendijarevic