Crimp Angle Research Articles

An Empirical Investigation into the Influence of Sealing Crimp Geometry and Process Settings on the Seal Integrity of Traditional and Biopolymer Packaging Materials

This article presents the results of investigations to determine how process settings and crimp geometry affect the seal strength and integrity of traditional polyolefin and biopolymer flexible packaging materials. The results show agreement with previous studies where temperature and dwell time are found to be the dominant factors for both polyolefin and biopolymer films. Pressure and crimp geometry are shown to be secondary factors in the process, up to the point of squeezing the film into molecular contact. In general, it is shown that biopolymers exhibit similar sealing characteristics to more traditional films. Regarding the sealing crimp geometry, it is shown that the crimp pitch has little or no effect on sealing integrity for films with gauges between 25 and 40 µm. However, for the same gauge material, crimp angles more than 80° offer the greatest potential to gain higher seal strengths. It is further shown that with the cellulose and polylactic acid films tested, a higher seal strength can be produced with crimp pitches of 2 mm and lower. Also presented are some more general implications for guiding the selection of sealing crimp geometry and their usage with biopolymers. Copyright © 2012 John Wiley & Sons, Ltd.

OS0602 CFRP開繊織物積層材の力学的特性に関する研究

Woven fabric composites with spread tow may induce better resin mechanical properties than the conventional woven architectures. The tow structure makes it possible to insert more carbon fiber into a given volume. And, the straight fibers with reduced crimp angle optimize and strengthen the composite. Furthermore, fewer crimps in the composite reduce the amount of excess plastic, which minimizes weight. However, the mechanism of woven fabric composites with spread tow has not been investigated completely. To estimate the effect of a CFRP woven laminates with spread tow, we have carried out the static bending test for woven fabric composites with/without spread tow. As a result, the characterization of a woven fabric composites with spread tow have characteristics is different from that of conventional woven laminates. And, it is revealed that the mesh superposition method is useful for the estimation of mechanical properties for woven fabric composites with spread tow.

Parametric study of the effect of microstructure on creep of plain weave composites

While the effect of microstructure on elastic properties and failure behavior of woven composites has been studied before, its effect on creep of woven composites has not been studied. Hence, a parametric study of the effect of microstructure on tensile creep of plain weave composites was pursued. The microstructure of F263/T300 plain weave composites was characterized experimentally and the range of values for various parameters that define the microstructure of the plain weave composite was obtained. Using these values, experimental creep data for unidirectional lamina, and a modified equivalent laminate model (MELM), tensile creep of woven composite, under on-axis and off-axis loading, was predicted and evaluated. For the range of crimp angle (15.2–19.5°) encountered in this composite, an increase in crimp angle increased both the instantaneous compliance and the magnitude of creep. The effect of crimp angle on creep was more under on-axis than under off-axis loading.

Finite element modelling of tow geometry in 3D woven fabrics

A finite element model of a 3D woven angle interlock fabric undergoing compaction based on the multi-element digital chain technique has been developed. The aim was to create a kinematic model to predict the internal architectural features in a commercial off-the-shelf code. A statistical analysis of yarn crimp and resin channel size was carried out on sections from the model at increasing levels of compaction and compared to laboratory-manufactured samples with the same weave style. Results show a good correlation between overall mean crimp values in the warp, weft and weaver yarns as well as reasonable accuracy in the frequency distribution of local crimp angles. The trend in resin channel size with respect to increasing levels of compaction was also good but significant discrepancies in the absolute dimensions of a resin channel were present due to limitations in controlling the yarn bundle internal interactions in the model.

Micromechanical models of helical superstructures in ligament and tendon fibers predict large Poisson's ratios

Experimental measurements of the Poisson's ratio in tendon and ligament tissue greatly exceed the isotropic limit of 0.5. This is indicative of volume loss during tensile loading. The microstructural origin of the large Poisson's ratios is unknown. It was hypothesized that a helical organization of fibrils within a fiber would result in a large Poisson's ratio in ligaments and tendons, and that this helical organization would be compatible with the crimped nature of these tissues, thus modeling their classic nonlinear stress–strain behavior. Micromechanical finite element models were constructed to represent crimped fibers with a super-helical organization, composed of fibrils embedded within a matrix material. A homogenization procedure was performed to determine both the effective Poisson's ratio and the Poisson function. The results showed that helical fibril organization within a crimped fiber was capable of simultaneously predicting large Poisson's ratios and the nonlinear stress–strain behavior seen experimentally. Parametric studies revealed that the predicted Poisson's ratio was strongly dependent on the helical pitch, crimp angle and the material coefficients. The results indicated that, for physiologically relevant parameters, the models were capable of predicting the large Poisson's ratios seen experimentally. It was concluded that helical organization within a crimped fiber can produce both the characteristic nonlinear stress–strain behavior and large Poisson's ratios, while fiber crimp alone could only account for the nonlinear stress–strain behavior.

A study on the compressive characteristics of co‐cured foam‐composite sandwich structures according to the crimp angle variations

AbstractA foam‐composite sandwich column composed of two‐ply carbon/epoxy fabric prepreg as a skin and PVC foam for a core material was investigated to determine the effect of crimp angle variations of the fabric prepreg on the compressive characteristics of the sandwich column. The crimp angle of the composite skin was observed and measured in terms of the forming pressure and the foam density as correlated with the foam deformation regimes. End compression tests for the foam‐composite sandwich columns were carried out to obtain the values of the compressive modulus and strength depending on the crimp angle variations. From the tests and observation results, it was found that the crimp angle and compressive strength were highly correlated; as the crimp angle increased, the compressive strength decreased as a large‐crimp angle caused the composite skin to fail due to simple microbuckling of the longitudinal tows. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Prediction of in-plane stiffness properties of non-crimp fabric laminates by means of 3D finite element analysis

Non-crimp fabric (NCF) composites are constituted by differently oriented layers of ideally unidirectional fibre tows. However, a slight waviness always appears in the tows. The applicability of the general laminate theory (GLT) to obtain the stiffness properties of NCF laminates is elucidated in this paper. For this purpose, a 3D finite element (FE) model of the representative unit cell (RUC) of a single NCF lamina has been carried out to obtain its apparent stiffness properties, which are employed, along with the GLT, to determine the stiffness properties of the laminate. These properties are compared with those obtained from the FE model of the RUC of the whole laminate for several configurations with different stacking sequences, fibre contents and crimp angles. Finally, predictions are compared with existing experimental results. The numerical results achieved validate the use of the GLT in NCF composites, once the lamina properties have been calculated taking into account the internal structure of these materials.

2625 テキスタイルグリーンコンポジットの引張変形特性(S23-3 グリーンコンポジットの特性評価(2),S23 バイオマス由来材料の成型加工と特性評価)

In recent years, research and development of materials using biomass sources are much expected to construct sustainable society. The so-called green composite (GC) consisting of natural fibers and biodegradable resin, is one of the most promising materials in biomass ones. The purpose of this study is thus to develop a textile GC material using ramie woven fabrics, and clarify its deformation behavior and mechanical properties. Generally, it is said that deformation behavior of textiles is determined by fabric density, crimp angle of yarns, yarn twisting and so on. Therefore, this study focuses on how these parameters affect the deformation behaviors and mechanical properties of the composite. The results show that larger fabric density brings the higher tensile strength and Young's modulus, while it reduces the fracture strain.

In-plane directional mechanical properties of carbon fabric skins in sandwich structures after thermoforming

In this paper, a representative unit volume finite element (RUV FE) model was employed to simulate thermoforming process of carbon fabric-polymeric foam sandwich structures. Thermoforming simulations, which capture crimp angles and amplitude changes of carbon fabric with respect to different operational pressure, were conducted with the help of RUV FE model. Micro-deformation of tow structures after thermoforming was rigorously reflected in the second stage FE model to determine the in-plane directional stiffness of skin parts. Tensile tests were carried out to investigate mechanical properties of skin parts in sandwich structures for the potential usage of automotives, electronic housings or the satellite structure design.

The relation between compressive strength of carbon/epoxy fabrics and micro-tow geometry with various bias angles

In this paper compressive tests of carbon/epoxy (plain weave, 3k) fabric composites were performed to investigate the relation between compressive strength and various bias angles and shear angles. Compressive properties such as chord modulus and maximum strength of the fabric composite materials are essential to analyze the drape behaviour and estimate the quality of the final products. Various specimens with different bias and shear angles which were fabricated by using autoclave de-gassing moulding process were prepared to estimate the strength and chord modulus with respect to the bias and shear angle variations. The stacking sequences of the compressive test specimens are [0] 10 T , [15] 10 T , [30] 10 T and [45] 10 T for bias specimens and [±37] 10 T , [±32] 10 T , [±28] 10 T , [±22] 10 T for sheared specimens. Micro-tow structures were observed to correlate the fabric compressive strength with crimp angle. Anti-buckling rig was involved to prevent specimens from buckling during the compressive tests. The compressive test was performed with 1.3 mm/min strain rates. Compressive test results were compared with calculation results. Facture modes which were classified in two different modes were analyzed using microscopic observation.

Changes in tow geometry of plain‐weave carbon/epoxy fabrics draped onto compliant hemisphere molds

AbstractIn this study, draping of carbon/epoxy fabrics (Plain weave, 3k) onto hemisphere molds is studied to understand the deformation behavior of fabrics during thermoforming. In order to characterize the local deformation of fabrics draped onto hemisphere molds, specimens are selected and prepared for microscopic observation. Several tow parameters such as crimp angle and tow amplitude are investigated to determine the effect of forming conditions and material properties of molds on the microstructures of fabrics during draping and forming. The measured parameters were normalized with respect to an undeformed specimen to facilitate a comparison between specimens. Hemisphere molds made of aluminum and PVC foam are used to observe the effect of mold compliance on microstructural changes during forming. The stress–strain behavior of the foams are measured to correlate the behavior of micro‐tow structures with the foam properties. It is found that some of the tow deformation during shearing is significantly altered when using the compliant foam mold. Polym. Compos. 27:111–118, 2006. © 2006 Society of Plastics Engineers.

Influence of Different Woven Geometry in Poly(propylene) Woven Composites

AbstractSummary: The difference between the melting temperatures of poly(propylene) (PP) fibre and random poly(propylene‐co‐ethylene) (PPE) was exploited in order to establish processing conditions for an all PP composite. Under these conditions the matrix must be a liquid in order to ensure good wetting and impregnation at the fibres, though the temperature must not be too high to avoid melting the fibres. The high chemical compatibility of the two components allowed creation of strong physico‐chemical interactions, which favour strong interfacial adhesion. The static and dynamic mechanical properties and morphology of poly(propylene) woven fabric reinforced random PPE composites have been investigated with reference to the woven geometry that influenced the properties of the woven composites. Among the various cloth architectures that were used in the PP‐PPE composites, the satin weave imparted overall excellent mechanical properties due to the weave parameters, such as high float length and fibre count, low interlace point and crimp angle, etc. Morphology of the composite has been investigated by macro photography and scanning electron microscopy. Images from scanning electron microscopy provided confirmation of the above results by displaying the consolidation and good fibre‐matrix wetting of the composites.Loss modulus of poly(propylene) woven‐matrix composites with different types of woven geometry.magnified imageLoss modulus of poly(propylene) woven‐matrix composites with different types of woven geometry.

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 4. Morphometric, microscopic and biomechanical properties of the digital tendons of the forelimb

AIM: To determine the weight, volume, density and cross-sectional area (CSA) of the digital flexor tendons, common digital extensor tendon (CDET) and suspensory ligament (SL) of the forelimb of young Thoroughbred horses in early training, and to assess the response to a training programme of known parameters of superficial digital flexor tendon (SDFT) tissue at mid-metacarpal level. METHODS: The tendons of seven 2-year-old Thoroughbred horses in training were inspected, transected into segments of known length, and compared with those from seven untrained horses matched for age, sex and breed. The weight, volume, density and CSA of each segment, and the crimp angle, histological features, and biomechanical ultimate stress and stiffness of tendon samples from the mid-metacarpal region of the SDFT were determined. RESULTS: There was no macroscopic evidence of swelling or discolouration in any of the tendon segments or cut surfaces. The volumes of SDFT and CDET segments of horses in the trained group were significantly greater than those in the untrained group (p=0.036 and p=0.039, respectively). A greater increase in volume than weight resulted in a lower density in the SDFT but not CDET in trained compared with untrained horses (p=0.038). CSA of these two tendons was significantly greater in the trained group (p=0.002 and 0.036, respectively), the percentage increase being greater in the CDET than the SDFT. The number of tenocytes at four sites in the mid-metacarpal SDFT region was less in trained than untrained horses (p=0.025). There was no histological evidence of inflammation, and no difference in crimp angle between groups. There was no significant between-group difference in stiffness or ultimate stress of tendon strips. CONCLUSIONS: Volume and CSA of the SDFT and CDET were larger in trained than untrained horses. The SDFT was less dense in the trained group. Because no evidence of tendonitis was detected and training appeared to have no significant effect on crimp angle or biomechanical properties of tendon strips, the size and density changes were presumed to be adaptive and induced by the training. CLINICAL RELEVANCE: Although evident in this in vitro study, the detection of adaptive from initial pathological increase in size of the SDFT is likely to be difficult in vivo.

Collagen fibres of the spontaneously ruptured human tendons display decreased thickness and crimp angle

Purpose. To study collagen fibre thickness and crimp formation in healthy and ruptured human tendons. Methods. The thickness, crimp angle and wavelength of the collagen fibres were analyzed by interference and polarization microscopy and the samples were studied by transmission and scanning electron microscopy in four different healthy human tendons (Achilles, Quadriceps, Biceps brachii and Extensor pollicis longus) and in 66 spontaneously ruptured tendons. Results. In the normal (healthy) tendons, the diameter and crimp angle of the collagen fibres varied greatly between the four different tendons, the thickest fibres with the largest crimp angle being in the Achilles and Quadriceps tendons, whereas the Biceps brachii and Extensor pollicis longus, tendons that bear lighter strains but carry functions of high specificity, were found to have substantially smaller collagen fibres with lower crimp angle. Ruptured tendons had significantly smaller collagen fibre diameter than the normal tendons, the fibre diameter being −36% in comparison to their healthy counterparts in the Achilles tendons ( P<0.0001), −24% in the Quadriceps tendons ( P<0.0001), −37% in the Biceps brachii ( P<0.0001) and −14% in the Extensor pollicis longus ( P=0.10), respectively. Similarly, the crimp angle of the collagen fibres was also found to be lower in the ruptured tendons than in healthy, normal tendons. Further, the collagen fibres in the ruptured human tendons showed great variation in the crimp angle between the adjacent fibres and in the successive crimps of the same fibre. Conclusion. Our results show that spontaneously ruptured tendons display focal regions with decreased collagen fibre thickness, decreased crimp angle and disrupted crimp continuity, microscopic alterations that possibly result in reduced strength of the tendons being less resistant to tensile forces, and thus, place them at increased risk of ruptures.

Histochemical and ultrastructural study of collagen fibers in mouse pubic symphysis during late pregnancy

Reference is usually made to the parallel orientation towards the main line of exerted tension at the pubic joint in mice, for supporting forces applied to the joint. Despite the wealth of morphological information about the extracellular matrix in this joint, little is known regarding the involvement of the crimp of collagen fibers in the dramatic transformations occurring in this region during the last 3 days of pregnancy. Examination of the collagenous architecture suggests that the biomechanical properties are directly related to fibril diameters, composition of ground substance and changes in the bundle morphology, particularly in the crimp structure. The purpose of this study was to further describe the transformation of the collagen fibers of the pubic symphysis during late mouse pregnancy. We examined the architecture of collagen fibers in the symphysis and pubic ligament through the Picrosirius-polarization method and also through scanning electron microscopy to directly visualize and measure the crimping from pregnant and virgin mice. The crimp angle and the length of five consecutive crimps were measured according to Patterson-Kane et al. [Connect. Tissue Res. 36 (1997) 253]. It could be demonstrated that the angles progressively decreased and the crimp length increased, denoting that the fibers have untwisted during the relaxation process. Our findings suggest that a disruption of the helical arrangement of the collagen containing fibers may contribute to explaining the rapid remodeling that occurs at the end of pregnancy and that is responsible for an increase in pliancy and length of the pubic ligament in mice.

Mechanical Behavior of Circular Hybrid Braids Under Tensile Loads

In this work, the mechanical behavior of hybrid circular braids without a core under tensile loads is studied experimentally and analytically. A predictive model of the mechanical response of the braids based on the constituent yarn characteristics and machine parameters is developed. The structural geometry of the fabric is analyzed and used to build the mechanical model. Image analysis is employed to experimentally characterize the structural parameters of the braids, their deformation, and the braid and crimp angles of the yarps. Hybrid braids with two different yarn systems are manufactured at various braid angles. The structures are tested in tension and their strain response is recorded. Experimental results are compared to theoretical values, and the model predic tions have good accuracy. In the case of high braid angles, the theoretical model underestimates the strength of the fabric.

Three-dimensional stress analysis of textile composites. Part II: Asymptotic analysis

An asymptotic singular stress analysis was performed in the unit-cell of the plain–woven composite in the vicinity of the yarn–yarn–matrix interface intersection with and without the inter-yarn delamination. The problem was reduced to a three-material wedge singularity type by introducing several curvilinear coordinate systems and systematic expansions in power series of the distance from the contour of the stress singularity. The power of stress singularity at the inter-yarn and yarn–matrix interface junction was investigated as a function of crimp angle and matrix-to-yarn stiffness ratio. In the case of perfect bonding between the yarns and the matrix with small crimp angles near 9°, the power of singularity is weak (∼0.02) and insensitive to the stiffness ratio of the axial yarn to the matrix material. For increased crimp angles, however, small variations in the stiffness of the matrix material can significantly affect the power of singularity. In the case of the inter-yarn delamination, two singular roots––one crack type (∼0.5) and one weak (∼0.01)––were obtained for all crimp angles and delamination opening modes. Coefficients of the asymptotic expansion were obtained by comparing the full-field three-dimensional numerical solution based on B-spline displacement approximation method with multi-term asymptotic expansions in the vicinity of the singular point. Good agreement between the two solutions was observed in all examples considered.

Effect of fiber geometry on the elastic constants of the plain woven fabric reinforced aluminum matrix composites

The geometric and elastic models based on the unit cell have been proposed to predict the geometric characteristics and the elastic constants of plain woven carbon fabric reinforced metal matrix composites. In the geometric model, the inclined angle of the yarn crimp and the fiber volume fraction of woven composites have been predicted. In the elastic model, the coordinate transformation has been utilized to determine the elastic constants of the yarn crimp. The effective elastic constants have been obtained from the volume averaging of the elastic constants for constituent materials in composites. In order to verify the proposed model, plain woven carbon fabric reinforced Al matrix composites were fabricated using the vacuum assisted pressure infiltration casting process. Resonant ultrasound spectroscopy was performed to measure the effective elastic constants of the composites. Good correlation between the model predictions and the experimental results has been observed. Parametric study has been conducted to investigate the effect of various geometric parameters of plain weaves on the elastic constants of the composites. The yarn crimp angle, the gap length, fiber bundle size, the shape of yarn section, and the constituent materials have been examined in this study. Based on the proposed model, the effect of various geometric parameters and constituent materials on the three-dimensional elastic properties of woven fabric reinforced composites can be reasonably predicted.

Microscopic investigation of tow geometry of a dry satin weave fabric during deformation

In this paper the changes in tow geometry during deformation of dry woven carbon-fibre satin-weave fabric are measured and correlated with the in-plane forces applied. The evolution of geometric tow parameters such as tow spacing, crimp angle, tow amplitude and wavelength is investigated. To observe the change in the fabric architecture, specimens from bias extension, biaxial and picture frame tests are sectioned and observed under the microscope. It is found that the different loading conditions cause differences in the evolution of tow architecture during deformation, in particular affecting the onset of ‘lock-up’. (At lock-up interactions between tows prevent further significant shear deformation.) In one picture frame test the fabric is deliberately misaligned with respect to the sides of the frame so that, during subsequent deformation, one set of tows is under tension, while the other is compressed. There is a significant difference in behaviour between the two sets of tows. The variation in deformed tow geometry with shear angle is fitted using a simple parametric model.

Collagen fibril size and crimp morphology in ruptured and intact Achilles tendons.

The present study examined the hypothesis that collagen fibril diameter and crimp angle in ruptured human Achilles tendons differed from that of intact ones. Tissue samples were obtained from the central core (distal core) and the posterior periphery (distal superficial) at the rupture site, and the proximally intact (proximal superficial) part of the tendon in 10 subjects (38+/-8 years) with a complete tendon rupture. For comparisons corresponding tissue samples were procured from age (38+/-7 years) and gender matched intact Achilles tendons during routine forensic autopsy. The cross-sectional area density and diameter distribution of fibrils were analyzed using stereological techniques of digitized electron microscopy biopsy cross-sections, while crimp angle was measured by the changing banding pattern of collagen fibers when rotated between crossed polars. Nine of 10 persons with tendon ruptures reported that the injury did not occur during exceedingly large forces, and none experienced any symptoms in the days or months prior to the injury. Fibril diameter distribution showed no region-specific differences in either the ruptured or intact tendons for either group. However, in the distal core there were fewer fibrils in the ruptured compared to the intact tendons in 60-150 nm range, P<0.01. Similarly, in the distal superficial portion there were fewer fibrils in the ruptured compared to the intact tendons in the 90-120 nm range, 2P<0.05, while there were no differences in the proximal superficial tendons. Crimp angle did not display any region-specific differences, or any difference between the rupture and intact tendons. In conclusion, these data suggest that although crimp morphology is unchanged there appears to be a site-specific loss of larger fibrils in the core and periphery of the Achilles tendon rupture site. Moreover, the lack of symptoms prior to the rupture suggests that clinical tendinopathy is not an etiological factor in complete tendon ruptures.