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Three-dimensional spacer fabric is a type of one-piece sandwich structure consisting of two outer layers and vertical and inclined spacer monofilaments. It behaves like a cushioning material, having linear, plateau, and densification stages under compression. This article elucidates the compression mechanism of a typical spacer fabric in terms of global deformation, local deformation, and internal contact behavior of spacer monofilaments through finite element simulation. While the linear stage is post-buckling of spacer monofilaments with tight constraints, the plateau stage is a combination of post-buckling, torsion, rotation, and contact of spacer monofilaments. The densification stage is attributed to the contact between spacer monofilaments and outer layers, which decreases the effective length to bear the load and enhances the constraints on the spacer monofilaments. The vertical spacer monofilaments with almost triple the normal strains of the inclined ones contribute more to compression resistance. [ABSTRACT FROM AUTHOR]

Auxetic fabrics are becoming a tempting option for many modern textile products due to their unusual deformation behavior under tensile load. In spite of the developments that have been made, it remains difficult to produce auxetic fabrics more efficiently using existing technologies. In this research, a novel type of auxetic fabrics is proposed based on rotating square geometry and manufactured using commercially available raw materials and lamination technique. Rotating square structures with different parameters are firstly produced through laser cutting a frame fabric, and then bonded to a base fabric using a hot-melt adhesive membrane. Tensile tests are conducted on various two-layer and three-layer laminated fabrics to investigate their deformation behaviors and auxetic effects. Results show that the auxetic behavior of the laminated fabrics mainly depends on initial modulus difference between the base material and the laminated frame material and can be affected by the initial intersection angle and size of square units. It is also found that three-layer laminated fabrics are more desirable than two-layer laminated fabrics when it comes to avoiding out-of-plane deformation and extending tensile strain range of auxeticity. [ABSTRACT FROM AUTHOR]

This paper aims to identify the underlying physical mechanism for the compression deformation of a warp-knitted spacer fabric with a typical structure with experimental and theoretical studies. Compression tests were carried out to measure the load–displacement relationship of the fabric. The structural features of the spacer yarns were photographed by a microscope at different displacements during the compression test. A theoretical model based on elastica theory was developed to describe the compression behavior of the fabric by introducing the effect of complex geometry of the spacer yarns. A comparison between the experimental results and theoretical calculations was also conducted. Four distinctive stages including initial stage, elasticity stage, plateau stage and densification stage were identified and their underlying physical mechanisms were explained based on experimental observations and theoretical calculations. The model could provide an in-depth understanding on the deformations of spacer yarns of spacer fabrics under compression. [ABSTRACT FROM AUTHOR]

• This study developed a heterogeneous 3D virtual rutting model. • The model can investigate the rutting mechanism and meso-mechanical responses. • Innovative algorithms were proposed for cyclic rolling loading. This study proposed a heterogeneous 3D virtual rutting model to investigate the rutting evolution mechanism and the dynamic meso-mechanical response of a porous asphalt mixture composite structure. The 3D virtual rutting test model incorporated a three-phase asphalt mastic-aggregate-airvoids system with grain size distribution and genuine aggregate morphology. Innovative algorithms were developed for cyclic rolling loading to reflect repetitive wheel loading. In contrast to the indoor rutting tests, the 3D virtual rutting tests exhibited greater rutting deformation and weaker dynamic stability in the range of 3.16%–10.17% and 2.65%–11.77%, respectively. Shear forces were predominant in the virtual rutting tests. As the porous asphalt mixture composite structure's surface layer thickness increased, the shear contact force increased and the maximum parallel-bond (PB) contact force diminished. The 3D virtual rutting test model was demonstrated to be feasible for simulating rutting deformation and dynamic meso-structural responses in porous asphalt mixtures with cyclic rolling loading algorithms. [ABSTRACT FROM AUTHOR]

• Python image processing algorithms for separating aggregates and asphalt mastic. • 2D Python-developed virtual model was proposed to analyze rutting mechanism. • Pioneered the interaction between PFC2D and Python. This study developed a novel 2D virtual rutting model to analyze the permanent deformation mechanism and the micromechanical response of asphalt mixtures. Digital samples of asphalt mixture were image-processed by Python-based algorithms to effectively segment coarse aggregate and asphalt mastic. The Python processed images were imported into PFC2D to establish a 2D virtual rutting model that incorporated the aggregate morphology, the aggregate gradation, and the aggregate void distribution. The feasibility and accuracy of the 2D virtual rutting model were validated by macroscopic laboratory rutting tests. The 2D virtual rutting test had 6.22% higher dynamic stability and 2.12% lower rutting deformation than the laboratory indoor rutting test. As rutting depth increased, the number of effective contacts declined to a steady value. The average Burger contact force between particles within the rutting model increased as loaded. Results demonstrated that the 2D virtual rutting test model was capable of simulating the time-dependent rutting deformation by incorporating Python-coupled algorithms to process aggregates' topography characteristics. [ABSTRACT FROM AUTHOR]

The room temperature creep behaviors and related microstructural changes of a high‐tenacity (HT) poly(ethylene terephthalate) (PET) industrial yarn and a super‐low‐shrinkage (SLS) PET industrial yarn were investigated and compared by using wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering (SAXS), birefringence measurements and Fourier transform infrared spectroscopy (FTIR) in order to identify their respective underlying creep mechanisms. The crystal structure including crystalline orientation and crystallinity of fibers did not show obvious changes after the creep process, while the amorphous structures varied with creep stress. The HT yarn creep deformation was mainly elastic, and its creep recovery ratio was high. The amorphous orientation, amorphous layer thickness and degree of conformation change from gauche to trans conformers showed a slight increase. The mechanism of this slight change is that the coiled molecular chains are oriented under tensile loading and most of the extended chains are disoriented under offloading in the small amorphous region. By contrast, the SLS yarn underwent plastic creep deformation with a low recovery ratio. After the creep test, the amorphous orientation and lamellar thickness both increased but the crystallinity remained unchanged. The creep mechanism for the SLS yarn is that the molecular chains in the large amorphous domain are easily extended and oriented subjected to tensile loading, while conformation transition from gauche to trans conformers and the formation of irreversible mesophase take place. © 2018 Society of Chemical Industry The relationship between creep behaviors and microstructures of HT and SLS yarns is investigated. Different creep mechanisms are proposed in that an obvious increase of lamellar thickness is induced from the formation of stable mesophase in the SLS yarn. [ABSTRACT FROM AUTHOR]

This paper aims to identify the creep mechanisms of high tenacity (HT) polyester industrial fiber under different loads. In-situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) tests were conducted on a 1000 D HT fiber during the creep and creep recovery process with a low load (15 N) and a medium load (50 N) as well as creep rupture process with a high load (60 N). The measured creep strain-time curves comprised tensile zone (I), creep deformation zone (II) and creep recovery/rupture zone (III). The SAXS indicated that the macroscopic initial creep strain in zone I and creep deformations in zone II were attributed to conformation transition from gauche to trans in amorphous region, increasing the amorphous orientation and long period. Irreversible portion of conformation changes accounts for the small unrecoverable plastic creep strain after removing 15 N load in zone III. The initial creep strain in zone I and creep deformations in zone II of the 50 N creep process were bigger than the microscopic long period strain, because amorphous layers had conformational transformation and microfibril slippage which also produced a higher unrecoverable plastic creep strain in zone III. The long period increased significantly at the beginning of rupture zone with 60 N due to fragmentation of amorphous tie molecular. The disappearance of lamellar peaks at the end of rupture zone implied destruction of periodic lamellar structures, for the entire breakage of amorphous chains. The WAXS suggested that the crystal structure was stable under the creep loads. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the protective properties of warp-knitted spacer fabrics developed for protecting the human body on impact. A drop-weight impact tester was used to test the fabrics in a hemispherical form to simulate the use of impact protectors in real life. The study consists of two parts. The first part, presented in the current paper, focuses on the impact behavior of a typical spacer fabric impacted at different levels of energy. The analysis includes the impact process and the energy absorption and force attenuation properties of the spacer fabric. Frequency domain analysis is also used, to identify the different deformation and damage modes of the fabric under various levels of impact energy. The results show that the impact behavior of the fabric under impact in the hemispherical form is different from that in the planar form. The results also indicate that the curvature of the fabric can reduce energy absorption during the impact process and therefore reduce the force attenuation properties of the spacer fabric. This study provides a better understanding of the protective properties of spacer fabrics. The effect of fabric structural parameters and lamination on the protective properties of spacer fabrics under impact will be presented in Part II. [ABSTRACT FROM PUBLISHER]

Deformation induced crystal–crystal transitionof polybutene-1 (PB-1) from forms II to I at different temperaturesis studied with in situ synchrotron radiation wide-angle X-ray scattering(WAXS). Analyses on the evolution of crystallinity and orientationsof forms II and I during tensile deformation show that stretch acceleratesthe transformation from forms II to I, which is interpreted basedon either a direct crystal–crystal transition or an indirectapproach via an intermediate state of melt, namely a melting recrystallizationprocess. A three-stage mechanical deformation including linear deformation,stress plateau, and strain hardening is observed in the engineeringstress–strain curves, which corresponds to a process of incubation,nucleation, and gelation of form I crystals. It establishes a nicecorrelation between phase transition and mechanical behavior in thisstudy. [ABSTRACT FROM AUTHOR]

We designed and constructed an extensional rheometer for in situ small and wide angle x-ray study on flow-induced crystallization of polymer. Two rotating drums with an axis distance of 20 mm are employed to impose extensional deformation on the samples. With a constant angular velocity, the two drums generate a constant Henkcy strain rate as sample length for testing keeps constant during deformation. An ionic liquid is used as heating medium to prevent polymer melt from bending downward due to gravity, which is excellent in terms of high thermal stability, low viscosity, and relative low adsorption on x-ray. Flow-induced crystallization experiments are conducted with this apparatus on x-ray scattering station in Shanghai Synchrotron Radiation Facility (SSRF), which allows us to collect rheological and structural data simultaneously and may lead to a better understanding on flow-induced crystallization of polymer. [ABSTRACT FROM AUTHOR]

As fundamental load-bearing parts, the cylindrical steel structures of transmission towers relate to the stability of the main structures in terms of topological relation and performance. Therefore, the periodic monitoring of a cylindrical steel structure is necessary to maintain the safety and stability of existing structures in energy transmission. Most studies on deformation analysis are still focused on the process of identifying discrepancies in the state of a structure by observing it at different times, yet relative deformation analysis based on the data acquired in single time has not been investigated effectively. In this study, the piecewise cylinder fitting method is presented to fit the point clouds collected at a single time to compute the relative inclination of a cylindrical steel structure. The standard deviation is adopted as a measure to evaluate the degree of structure deformation. Meanwhile, the inclination rate of each section is compared with the conventional method on the basis of the piecewise cylinder fitting parameters. The validity and accuracy of the algorithm are verified by real transmission tower point cloud data. Experimental results show that the piecewise cylinder fitting algorithm proposed in this research can meet the accuracy requirements of cylindrical steel structure deformation analysis and has high application value in the field of structure deformation monitoring. [ABSTRACT FROM AUTHOR]