Micro-SAXS and force/strain measurements during the tensile deformation of single struts of an elastomeric polyurethane foam

Martin, C.; Eeckhaut, G.; Mahendrasingam, A.; Blundell, D.J.; Fuller, W.; Oldman, R. J.; Bingham, S. J.; Dieing, Thomas

doi:10.1107/s0909049500005744

Cited by 13 publications

(7 citation statements)

References 16 publications

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“…11 An improved version of this cell, used in the present work, was developed by a Keele/ICI/ESRF collaboration for micro small-angle X-ray scattering. 12 In addition to the original design it incorporated an Entran strain gauge (0.5 N range) and a homemade tension control. The ends of a single fiber were twisted around half cylinders, which were fixed on the two yaws of the stretching cell.…”

Section: Methodsmentioning

confidence: 99%

X-ray Microdiffraction Study of Chain Orientation in Poly(p-phenylene terephthalamide)

Riekel¹,

Dieing²,

Engström

et al. 1999

Macromolecules

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Single fibers of poly(p-phenylene terephthalamide) (PPTA; trade names: Kevlar 29 , Kevlar 49 , and Kevlar 149 ) have been scanned through a 3 µm diameter X-ray beam and the degree of orientation (fc) determined at every point. All samples show a gradient in fc values from the skin to the core. The highest degree of orientation was found at the edges of the fibers. This effect is particularly strong for Kevlar 29 . In addition, ripples in orientation were observed along the fiber axis for Kevlar 29 , but on a smaller scale than the transversal gradient. Upon tensile deformation up to about 3 GPa applied stress, the transversal fc anisotropy is gradually reduced and disappears at the highest stress values. Kevlar 29 attains at about 1.5 GPa applied stress the same degree of orientation as Kevlar 49 .

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Section: Methodsmentioning

confidence: 99%

X-ray Microdiffraction Study of Chain Orientation in Poly(p-phenylene terephthalamide)

Riekel¹,

Dieing²,

Engström

et al. 1999

Macromolecules

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“…In this study we do not start from isotropic material like most of the papers do, but start from oriented, [ 16 ] injection-molded material that is investigated during a fi rst tensile test. We determine true stress and local strain of the sample at the position of X-ray irradiation.…”

Section: Tensile Testsmentioning

confidence: 99%

Structure and Mechanical Properties of an Injection‐Molded Thermoplastic Polyurethane as a Function of Melt Temperature

Stribeck

Zeinolebadi

Sari

et al. 2011

Macro Chemistry & Physics

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Thermoplastic polyurethanes (TPUs) molded at 205, 215, and 235 ° C are monitored by SAXS and WAXS during straining. A non-affi ne nanostructure deformation and related evolution mechanisms are found. DSC and microscopy are applied. DSC shows two melting endotherms. The results indicate that melts kept below the second peak stay phase-separated. The orientation parameter f ( ε ) and d f /d ε from WAXS are related to chain orientation mechanisms (strain ε ). SAXS shows hard domains that are only correlated to a next neighbor ("sandwich"). Thick sandwiches lengthen more than thin ones. Thin-layer sandwiches feature a strain limit. Some are converted into thick-layer sandwiches. Two materials have tough hard domains. Material processed at 235 ° C is soft and contains weak hard domains that fail for ε > 0.75. of the material. Block copolymers synthesized by living polymerization are characterized by uniform block lengths. Processing of such compounds may result in lattice-like nanostructures or even in photonic crystals, in which the soft and the hard blocks reside completely in different domains. This is different with thermoplastic polyurethanes (TPU). Along with their chains a mixed sequence of soft segments and hard segments is found. Thus, even optimum process control only leads to domains of very diverse shape and size, the arrangement of which can rarely lead to lattice-like correlation. Moreover, soft domains may contain several hard segments. Consequently, the chemistry [ 1 ] and the processing conditions [2][3][4][5] defi ne the nanostructure that, in turn, determines the material's mechanical properties. The hard domains form physical cross-links and make the material behave rubber elastic. Because the hard domains are permanent only to a fi rst approximation, the stressstrain behavior of TPUs is subject to "strong hysteresis, time dependence and cyclic softening". [ 6 ] Thus maturing or aging may become a problem, if longer time elapses between investigations with different methods, because in this case the results may not be combined.

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“…The origin of the energy loss lies in the mechanics of the elastomers that, during compression, rearrange their structure in a way that is not replicated elastically on unloading [9], but that reverts to the noload structure with a relaxation time of several seconds i.e. it recovers to 50 per cent of its unloaded dimension in 10 s. It may be reasonable [11] to imagine that the thin struts in the foam could perform in a manner that was dictated by size effects, since the polymer chain length is of the same order as the strut thickness. In fact, Martin et al [11] used a synchrotron X-ray source to look at the deformation of individual foam struts in a polymer foam and showed that they behave in a manner similar to bulk elastomers.…”

Section: Discussionmentioning

confidence: 99%

The Effect of Cyclic Loading on the Stiffness and Damping Factors in the Midsoles of Running Shoes

Walker

2006

Proceedings of the Institution of Mechanical Engineers, Part L:

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McMahon and Greene showed, in 1979, that it is possible to design a running track with a compliance that will reduce the shock loading on the legs of the athletes, and yet will enable them to return fast times. Since then, attempts have been made to find a combination of properties in a running shoe that would achieve the same ends. The extent to which the stiffness of the midsole may be reduced is limited by the need for the athlete's ankle to maintain a high degree of stability. On the other hand, it has been predicted from modelling studies that the damping properties of running shoe midsoles may be controlled to reduce the impact shock that is imparted to each leg of a runner, as the heel strikes the ground at the initiation of the contact phase.A method has been developed for deriving the damping parameters (logarithmic decrement and damping factor) from an analysis of the complete load deformation curve, both for a single cycle and after several thousand load cycles. The stiffness and damping properties of five types of running shoes have been measured under low frequency loading, and also at 1 Hz -close to the frequency of heelstrike. It was found that although the damping factors range from 0.02 to 0.04 at low frequency, they are reduced to a range between 0.013 and 0.03 when the load is cycled at 1 Hz. In a similar fashion, the stiffness values increased under cyclic loading, so that the energy absorbed by the midsole was reduced by about a factor of two. These findings were found to be repeated across all the types of shoes that were tested, and related to the basic deformation mechanisms in the polymers used in the midsoles.

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Micro-SAXS and force/strain measurements during the tensile deformation of single struts of an elastomeric polyurethane foam

Cited by 13 publications

References 16 publications

X-ray Microdiffraction Study of Chain Orientation in Poly(p-phenylene terephthalamide)

X-ray Microdiffraction Study of Chain Orientation in Poly(p-phenylene terephthalamide)

Structure and Mechanical Properties of an Injection‐Molded Thermoplastic Polyurethane as a Function of Melt Temperature

The Effect of Cyclic Loading on the Stiffness and Damping Factors in the Midsoles of Running Shoes

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