In general, stress and deformation tensors of anisotropic linear elastic materials are related by the fourth order compliance/elasticity tensor. It has been observed that in the case of a planar (2D) ...orthotropic material the off-diagonal component of the compliance tensor known as normal-shear coefficient is equal to one half of the derivative of corresponding tensile compliance with respect to the angle of rotation of coordinate axes. A detailed analysis of the transformation law for the components of the compliance tensor is given, including the proof that the same relation also holds in the general case of planar anisotropic materials. In the selected illustrative examples polar diagrams of tensile moduli and normal-shear coefficients are shown for representative cases of woven fabrics and textile composites.
Unlike many other engineering materials, deformational behaviour of fabrics is marked by specific nonlinearities. For the purpose of certain engineering analyses, nonlinearity can be approximately ...described by means of appropriate models. A number of possibilities in approximation of tensile nonlinearity are statistically analysed and compared for the representative selection of woven fabrics. Second-order parabolic approximation is estimated to combine simplicity and good accuracy for a selected woven fabric. It is then included into deformational analysis of specimen in asymmetric tensile loading, as the case representative for structural application of textile, where geometric conditions combined with material properties define the mechanical behaviour of the body. The results indicate the factors of stress concentration due to load eccentricity. Simulation of tensile test gives the theoretical prediction of apparent reduction in stiffness and strength of the specimen in terms of the load eccentricity.
Determination of Poisson’s ratio and shear module of complex, nonlinear elastic material, such as woven fabric, is a challenge for researchers in the field of textile mechanics. In the standard ...method of determining the Poisson’s ratio, the transverse fabric strain is measured by a 1% tensile extension. In this way, there is no information about changing the Poisson’s ratio at higher tensile extensions, and the methodology itself is unsuitable for larger extensions because of woven fabric buckling. In this research, a device has been designed, which can be built on a dynamometer and which has the ability to measure transverse forces in fabric during tensile test. A mechanical model is developed from which it is possible to calculate Poisson’s ratio throughout the fabric stress–strain curve.
Nonlinear tensile behavior of woven fabric is simulated using a simplified model of the basic cell in which tensile and bending resistances of the yarn are geometrically discretized. Geometry of the ...basic cell, which undergoes changes in the deformation process, is represented by the slope of the yarn. Geometric nonlinearity is accounted for by writing static equations in current configuration, and the corresponding nonlinear set of equations is solved incrementally. In order to compare the computed tensile curve with the one experimentally recorded in KES procedure of textile evaluation, residual deformation in unloading needs to be accounted for. This is done by introducing elastoplastic tensile response of the yarn into the nonlinear micromechanical model. In that way, the model covers both geometric and material nonlinearities in fabric deformation with a limited set of basic parameters. In order to refine the initial estimate of the parameters and make up for neglected secondary phenomena, the set of model parameters is optimized for best fit of computed and recorded tensile curves. The optimization is done using genetic algorithm. Very good accuracy is obtained, which seems promising for future engineering of woven fabrics.
Purpose - This paper aims to develop an efficient two-variable minimisation algorithm and to apply it in engineering optimisation of buttonhole reinforcements.Design methodology approach - An ...iterative extreme search is based on quadratic approximation of objective function, locating approximate solution at the minimum of corresponding elliptic paraboloid. Stress analysis is performed using plane stress finite element model. Optimal selection of geometrical parameters of buttonhole-type reinforcement is done in terms of balance between maximum stress and material consumption.Findings - Adopted minimisation algorithm is assessed in a selected test example and proven to perform well in comparison with methods available in literature. In the selected case two local minima have been found within the predefined optimisation domain, with slight difference in objective function values.Research limitations implications - Research is limited to homogeneous isotropic elastic model and a single representative load case. Objective function is restricted to two influence factors and predefined optimisation domain.Practical implications - The method can be useful for engineers practitioners in the branch of clothing technology as a tool for computational estimate of optimal design of structural reinforcements.Originality value - The main quality of the paper is in software fusion of finite element analysis and advanced optimisation algorithm. The proposed theoretical-numerical model is discussed in terms of applicability in parameter setting on buttonholer in garment production.
Purpose - The purpose of this paper is to investigate and illustrate the possibilities of a systematic engineering approach in the design of mechanical reinforcements in garments. A mechanical ...reinforcement can be designed using optimisation strategies.Design methodology approach - In this work, an iterative algorithm for minimum search based on parabolic approximations is proposed and applied in the optimisation of mechanical reinforcement in a selected model problem of a buttonhole type.Findings - Optimisation algorithm based on parabolic approximations, in conjunction with the finite element analysis, offers some promising possibilities as support for the decision-making process in the design of mechanical reinforcements. The selection of optimisation criteria - influence parameters and corresponding weight factors - remains of course to be studied and implemented by the clothing engineering experts.Research limitations implications - The intention in future work should be to optimise two or more geometric parameters simultaneously (multidimensional optimisation), and to produce a computer program for an automated optimum search.Practical implications - The contents of the paper could be useful for the experts in clothing engineering in the process of design or selection of the reinforcements of weak spots in textiles and garments.Originality value - This paper provides optimisation routes to the weak sports of mechanical reinforcements in textiles and garments.
Numerical simulation of textile flexibility testing Šomodi, eljko; Hursa, Anica; Rogale, Dubravko
International journal of clothing science and technology,
06/2003, Letnik:
15, Številka:
3/4
Journal Article
Recenzirano
A non-linear numerical simulation of a standard procedure for textile flexibility testing is performed using discretised beam bending model. Geometric non-linearity due to large deflections is traced ...using incremental method. Linear moment-curvature response is assumed, as well as constant curvature of a finite element of the beam. Numerical procedure is incorporated into a PC programme producing graphical results for the deformed shape of the specimen, non-linear load-deflection diagrams and internal force distributions in deformed state. Finally, the method is applied to compute the flexural stiffness of textile materials from the data produced by the standard procedure for flexibility testing.
Dijelovi tijela katkad su komprimirani tijesnom odjećom, obućom, zavojima i slično. Pritom je važno uravnotežiti funkcionalnost i udobnost te izbjeći negativan utjecaj na zdravlje. Za analizu ...pritiska uslijed tijesne navlake treba uzeti u obzir mehanička svojstva same navlake, kao i tkiva. Teorija debelostjene cijevi prilagođena je za slučaj kompozitnog cilindra s krutom jezgrom, kao približnog modela ruke ili noge, primjenom odgovarajućih rubnih uvjeta. Rezultati upućuju na utjecaj pripijenosti i elastičnih svojstava tkiva i obujmice na razinu i karakter naprezanja u tkivu.
The proposed solution for increased automation in clothing production by freezing the textile involves sewing operations in frozen state. The realistic applicability of such technology could be ...limited, amongst other issues, by the possible loss of mechanical properties of the sewing stitch performed in that way. This work represents an experimental investigation for the evaluation of the influence of textile freezing to possible changes of mechanical properties with respect to the normally performed sewing stitch. A series of standard extension tests are done on specimens of sewing stitches performed both in frozen state and in usual way for comparison. The differences in the results are analysed statistically for a representative textile material.
U radu je prikazana primjena numeričkih metoda na polju tekstilne i odjevne tehnologije. S obzirom na složenost rješavanja problema pada tkanina i odjeće, numeričke metode su našle primjenu u ...području tekstilne i odjevne tehnologije. Tkanine izložene djelovanju malih opterećenja ponašaju se složeno zbog svojih svojstava nehomogenosti, nekontinuiranosti, anizotropnosti i deformabilnosti, te je ta stanja teško egzaktno matematički opisati. Približnim izračunavanjem pomoću numeričkih metoda moguće je predvidjeti njihovo ponašanje. U radu su stoga opisane dosadašnje primjene numeričkih metoda i rezultati primjene na području tekstila i odjeće. Prikazane su osnovne postavke numeričkih metoda s matematičkog stanovišta, te njihovo prilagođavanje za primjenu i rješavanje problema na području tekstila i odjeće.
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