服装出口策略论文外文文献

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一、市场扩张与贸易增长动力当今国际贸易中，非农产品占世界贸易的80%,工业制成品是世界贸易的主流，而纺织品是其中最重要的组成部分。从1983年以来，世界服装出口贸易的增长速度超过了世界制成品出口增长速度，在各类产品中出口增长速度仅次于办公和通讯用品。在以SITC三位数计的产品中有10项纺织服装产品的出口增长排列世界250种贸易产品的前50名，是世界贸易中增长最快的产品。解除配额后将会有更多的产品进入贸易高速增长的行列。近年来，纺织品服装国际贸易的增长动力更多地来自生产能力转移和生产外包，而非市场绝对消费量的上升。在乌拉圭回合结束前的30年里，世界服装生产能力的一半已经从发达国家转到发展中国家。这种转移的主要动因来自发达国家与发展中国家工资成本的巨大差异。由于配额体制的存在这种转移是十分缓慢的。在乌拉圭回合达成取消配额的时间框架后，发达国家的纺织服装业加快了生产能力向生产成本低的国家和地区的转移，跨国间的贸易也随之大幅增加。上世纪90年代以来，纺织品特别是服装生产外包的发展，使纺织品服装贸易更加活跃，成为纺织服装产品贸易持续增长不竭的源泉。生产外包同样是发达国家利用发展中国家低成本生产优势，维持其在该领域存在的战略选择，但生产外包比生产能力的转移具有更深远的影响，是当前和今后一段时期纺织品服装国际贸易的主流。到2005年配额取消之日，发达国家向发展中国家生产能力的转移已基本完成，下一步发达国家通过使用信息技术，按照优化、快速、低成本的原则整合供货网络，这样将引发发展中国家之间的纺织服装业的调整和转移。原来纯粹为追求配额而建的生产能力很可能就失去存在的意义，这部分贸易很可能将被取代。另外，由于取消配额是在WT0多边体制下实施的，这极大地冲击和削弱了一些双边或区域自由贸易协定给予特定国家的优惠和特权。一些由优惠和特权产生的贸易也将部分被取代。由此可见，取消配额后，生产和贸易扭曲将会被消除，贸易增长的原动力依然强劲。二、新的市场当纺织品服装贸易不再受到数量限制，世界将会出现一个巨大的、有待开发的市场，这个巨大的有待开发的市场不只存在于发达国家，也存在于发展中国家中。配额体制的瓦解毫无疑问将使发达国家市场变得更为开放，增加更多的贸易机会。但在配额取消后，发展中国家纺织服装市场也将变得进一步开放，其压力来自取消配额后的发达国家。发达国家认为,2005年后纺织品服装市场的开放基本上呈现一边倒的情况，发展中国家在这个行业中有很强的竞争力，但却保持着与之不对称的高关税，这种情形是不可持续的。发达国家希望多哈回合的一个主要目标是进一步大幅度降低关税和非关税壁垒，以便创造可比较的竞争机会，为长期增长奠定基础并使贸易惠及各方。为此发达国家都提出了针对纺织品、服装及鞋类产品的关税减让计划。欧盟甚至建议所有WTO成员大幅度降低关税，以使各成员间关税水平的差距保持在一个统一幅度内，并尽可能趋于零。欧盟此计划的目的是要发展中国家全面分担市场开放的责任。欧盟认为多哈回合的成功需要在考虑发展水平差异的情况下各方利益的全面平衡，而纺织服装产品将是所有成员利益全面平衡的主要部分。因此，发展中国家将被迫进一步开放其国内纺织品服装市场，新的市场将出现在东南亚较高收入的国家以及大的发展中国家内中高收入阶层。这些新的市场会成为未来发达国家纺织生产厂家的重要目标。另外新的市场也存在于发展中国家之间的贸易日益扩大。2001年发展中国家之间的贸易额共计6390亿美元，其中纺织服装530亿美元,1990年－2001年发展中国家之间纺织品和服装贸易的增长率分别为7%和11%。三、世界纺织服装贸易流向世界纺织品服装的贸易流向在乌拉圭回合后发生了较大的变化。在纺织品贸易上，两种趋势比较明显，一是传统的区域内贸易比重下降。西欧和亚洲这两个世界上最大的纺织品贸易市场各自内部交易比重都呈较大幅度的下降；二是发达地区增加了向发展中国家和地区输出纺织品的力度。1995年至2001年西欧向中东欧独联体国家以及北美向拉美地区出口纺织品的年增长速度分别高达12%和15%。在服装贸易上，最大的变化来自拉美向北美地区和中东欧独联体国家向西欧的出口。1995年至2001年拉美向北美市场和中东欧独联体国家向西欧国家出口的年平均增长率分别达到19%和16%,致使拉美对北美市场的依赖程度提高了个百分点。另外，亚洲对北美市场的依赖程度提高也较快，亚洲向北美的出口比重同期提高近10个百分点，而亚洲向欧洲的出口比重同期只提高了不足3个百分点。综合纺织品服装的贸易趋势可以看出，北美与拉美、西欧与中东欧独联体这两个区域的纺织服装业的整合已经初具形态。随着取消配额后日益增强的外部竞争，西欧内部贸易的下降不可避免，但取而代之的将是来自中东欧独联体国家甚至地中海、北非国家使用西欧面料生产的产品。北美市场也是如此。四、市场集中程度观察世界主要纺织品服装进口市场美国、欧盟、日本在1995年到2001年期间各自前5位的供应国和地区所占的贸易比重(见表2),可以得出两个重要的结论。第一，非配额国家进口纺织品服装市场的集中程度大大高于配额国家和地区。2001年日本前5大服装供应国已基本垄断了日本进口服装市场。相比之下美国前5大服装供应国占美国进口服装市场的一半都不到，而且这一比例在过去几年中还在下降。因此如果欧美取消配额，不论是纺织品还是服装，进口市场的垄断性将大为提高，即前5大供应国或地区所占的进口市场比例至少要达到80%左右。第二，在受配额管理的国家，进口纺织品的市场集中程度要高于服装，不论是美国还是欧盟都是如此。这表明上述两个国家和地区对服装进口的非关税壁垒要高于对纺织品，政府在服装贸易上的介入更多，尤其是美国。配额取消后的短期、中期内，欧洲、北美将仍然是世界最重要的服装市场，两者合计占世界服装进口的2/3。美国商务部做的一项研究表明，到2005年－2006年，主要买家将把为他们供货的国家减少一半，到2010年再减掉1/3。这就意味着有些国家、有些国营贸易商将会失掉原来拥有的市场。（

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这是一片写的不错的Effect of fiber architecture on flexural characteristics and fracture of fiber-reinforcVistasp M. Karbharia, Corresponding Author Contact Information, E-mail The Corresponding Author and Howard StrasslerbaMaterials Science & Engineering Program, and Department of Structural Engineering, MC-0085, University of California San Diego, Room 105, Building 409, University Center, La Jolla, CA 92093-0085, of Restorative Dentistry, Dental School, University of Maryland, Baltimore, MD, USAReceived 10 December 2005; revised 25 June 2006; accepted 31 August 2006. Available online 7 November aim of this study was to compare and elucidate the differences in damage mechanisms and response of fiber-reinforced dental resin composites based on three different brandsnext term under flexural loading. The types of reinforcement consisted of a unidirectional E-glass prepreg (Splint-It from Jeneric/Petron Inc.), an ultrahigh molecular weight polyethylene fiber based biaxial braid (Connect, Kerr) and an ultrahigh molecular weight polyethylene fiber based leno-weave (Ribbond).MethodsThree different commercially available fiber reinforcing systems were used to fabricate rectangular bars, with the fiber reinforcement close to the tensile face, which were tested in flexure with an emphasis on studying damage mechanisms and response. Eight specimens (n = 8) of each type were tested. Overall energy capacity as well as flexural strength and modulus were determined and results compared in light of the different abilities of the architectures flexural loading unreinforced and unidirectional prepreg reinforced dental composites failed in a brittle previous termfashion,next term whereas the braid and leno-weave reinforced materials underwent significant deformation without rupture. The braid reinforced specimens showed the highest peak load. The addition of the unidirectional to the matrix resulted in an average strain of mm/mm which is 50% greater than the capacity of the unreinforced matrix, whereas the addition of the braid and leno-weave resulted in increases of 119 and 126%, respectively, emphasizing the higher capacity of both the UHM polyethylene fibers and the architectures to hold together without rupture under flexural loading. The addition of the fiber reinforcement substantially increases the level of strain energy in the specimens with the maximum being attained in the braid reinforced specimens with a 433% increase in energy absorption capability above the unreinforced case. The minimum scatter and highest consistency in response is seen in the leno-weave reinforced specimens due to the details of the architecture which restrict fabric shearing and movement during is crucial that the appropriate selection of fiber architectures be made not just from a perspective of highest strength, but overall damage tolerance and energy absorption. Differences in weaves and architectures can result in substantially different performance and appropriate selection can mitigate premature and catastrophic failure. The study provides details of materials level response characteristics which are useful in selection of the fiber reinforcement based on specifics of : Fiber reinforcement; Dental composite; Flexure; Damage tolerance; Architecture; Unidirectional; Braid; Leno-weaveArticle Outline1. Introduction2. Materials and methods3. Results4. Discussion5. SummaryReferences1. IntroductionA range of fillers in particulate form have conventionally been used to improve performance characteristics, such as strength, toughness and wear resistance, Although the addition of fillers and recent changes in composition of resin composites have been noted to provide enhanced wear resistance [1] and [2], conventional filler based systems are still brittle as compared to metals. Sakaguchi et al. [3] reported that these were prone to early fracture with crack propagation rates in excess of those seen in porcelain. This is of concern since clinical observations have demonstrated that under forces generated during mastication the inner faces of restorations can be subject to high tensile stresses which cause premature fracture initiation and failure [4]. In recent years, fiber reinforcements in the form of ribbons have been introduced to address these deficiencies [5]. By etching and bonding to tooth structure with composite resins embedded with woven fibers adapted to the contours of teeth periodontal splints, endodontic posts, anterior and posterior fixed partial dentures, orthodontic retainers and reinforcement of single tooth restorations can be accomplished. While the science of fiber-reinforced polymer composites is well established, the application of these materials in dental applications is still new and aspects related to material characterization, cure kinetics and even placement of reinforcement are still not widely to the nature of filled polymer and ceramic systems that have been used conventionally, most material level tests designed and used extensively, for the characterization of dental materials, emphasize the brittle nature of materials response. In many cases the tests and the interpretation of results, are not suited to the class of fiber-reinforced polymeric composites, wherein aspects, such as fiber orientation, placement of fabric and even scale effects are extremely important. The difference in characteristics and the need to develop a fundamental understanding of response of continuous fiber and fabric, reinforced dental composites has recently been emphasized both through laboratory and clinical studies. Recent studies have addressed critical aspects, such as effects of fabric layer thickness ratios and configurations [6], fiber position and orientation [7] and even test specimen size [8]. However, the selection and use of continuous reinforcement is largely on an ad hoc basis, with diverse claims being made by manufacturers, without a thorough understanding of the materials based performance demands for the material by the specifics of an application (for example, the fabric architecture required for optimized performance of a post are very different from those for a bridge) or details of response characteristics at levels beyond those of mere “strength” and “modulus”. Further, each fabric is known to respond in different manner to manipulation and drape (. conformance) to changes in substrate configuration [9]. The architecture of the fabrics permits movement of fibers or constraint thereof and even shearing of the structure, to different extents. Weave patterns have also been noted to be important in the selection of composite materials for dental applications based on the specifics of application [10]. Thus, clinically, when each of the different fabric configurations is used to reinforce dental composites, there are manipulation changes that occur to some of the fabric materials. For the biaxially braided material, the fiber orientation can change after cutting and embedment in the composite when adapting to tooth contours. The fibers in the ribbon spread out and separate from each other and become more oriented in a direction transverse to the longitudinal axis of the ribbon. When the leno-weave is cut and embedded in dental composites, the fiber yarns maintain their orientation and do not separate from each other when closely adapted to the contours of teeth. However, due to the orthogonal structure gaps can appear within the architecture providing local areas unreinforced with fiber reinforcement. The unidirectional glass fiber material does not closely adapt to the contours of teeth due to the rigidity of the fibers. It is difficult to manipulate the fibrous material which leaves the final composite material thicker; further manipulation causes glass fiber separation with some visible fractures of the fibers aim of this study is to experimentally assess the flexural response of three commercial fiber/fabric reinforcement systems available for dental use and to compare performance based on different characteristics and to elucidate differences based on details of fabric architecture and fiber . Materials and methodsThree different fabric-reinforcing products, all in ribbon form, were used in this investigation. The first is a 3 mm wide unidirectional E-glass prepreg structure with no transverse reinforcement (Splint-It, Jeneric/Petron ) designated as set A, whereas the other two are formed of ultra-high molecular weight polyethylene fibers in the form of a 4 mm wide biaxial braid (Connect, Kerr), designated as set B and a 3 mm wide Leno-weave (Ribbond, WA), designated as set C. The first is a pure unidirectional which intrinsically gives the highest efficiency of reinforcement in the longitudinal direction with resin dominated response in the transverse direction. The second is a biaxial braid without axial fibers, which provides very good conformability and structure through the two sets of yarns forming a symmetrical array with the yarns oriented at a fixed angle from the braid axis. The third architecture has warp yarns crossed pair wise in a figure of eight pattern as filling yarns providing an open weave effect for controlled yarn slippage and good specimens of the fabrics were carefully measured and weighed and the average basis weight of the biaxial braid was determined to be × 10−4 g/mm2 whereas that for the leno-weave was × 10−4 g/mm2. It was noted that the unidirectional had an aerial weight of times that of the other two. Rectangular test bars of size 2 mm × 2 mm × 48 mm were constructed from layered placement of a flowable composite resin (Virtuoso FloRestore, Demat) in polysiloxane molds, with glass slides held on top with rubber bands and light cured for 60 s using a Kulzer UniXS laboratory polymerization lamp. In the case of sets B and C the fabric was first wetted and then placed on the first layer of the flowable composite resin such that the fiber reinforcement was placed between and mm from the bottom surface (which would be used as the tensile surface in flexural testing). The addition of higher modulus material at or near the tensile surface is known from elementary mechanics of materials to increase flexural performance and has been verified for dental composite materials by Ellakwa et al. [11] and [12]. Care was taken to maintain alignment of the fibers and fabric structure and not cause wrinkling or lateral movement which would affect overall performance characteristics. The fabric reinforced specimens had only a single layer of reinforcement near the bottom surface with the rest of the specimen having no fiber reinforcement. This general configuration for flexural specimens has been used previously by Kanie et al. [13]. In the current investigation, fiber weight fraction in the single layer was between 37 and 42% but is significantly lower if determined on the basis of the full thickness of the overall specimen. Unreinforced bars of the resin were also fabricated the same way for comparison and were designated as set specimens (n = 8) from each set were tested in three-point flexure using a span of 16 mm which provides a span to depth (l/d) ratio of 16, which is recommended by ASTM D 790-03 [14]. It is noted that flexural characteristics can be substantially affected by choice of the l/d ratio which intrinsically sets the balance between shear and bending moment, with shear dominating on shorter spans. Load was introduced through a rounded crosshead indenter placed in two positions—parallel to the test specimen span (P1) and perpendicular to the test specimen span (P2). The load head indenter was of 4 mm total length. This was done to assess effects of load introduction since ribbon architecture had fibers at different orientations. Tests were conducted at a displacement rate of 1 mm/min and a minimum of eight tests were conducted for each set. Loading was continued till either the specimen showed catastrophic rupture or the specimen attained a negative slope of load versus displacement with the load drop continuing slowly past peak to below 85% of the peak load. This level was chosen to exceed the mm/mm strain limitation of apparent failure recommended by ASTM D790-03 [14] so as to enable an assessment of ductility of the specimens. Specimens were carefully examined for cracking, crazing and other flexure strength was determined asClick to view the MathML source (1)where P is the applied load (or peak load if rupture did not occur), L the span length between supports and b and d are the width and thickness of the specimens, the tangent modulus of elasticity is often used to determine the modulus of specimens, by drawing a tangent to the steepest initial straight-line portion of the load-deflection curve to measure the slope, m, which is then used asClick to view the MathML source (2)in the current case a majority of the specimens show significant changes in slopes very early in the response curve indicating microcracking and non-linearity. Since these occur fairly early the modulus determined from the initial tangent has significant statistical variation. In order to determine a more consistent measure of modulus the secant modulus of elasticity as defined in ASTM D790-03 [14] is used herein, with the secant being drawn between the origin and the point of maximum load to determine the slope m, which is then used in Eq. (2). This also has the advantage of providing a characteristic that incorporates the deformation capability, thereby differentiating between specimens that reach a maximum load at low deformation (such as, the unreinforced composite and the unidirectional reinforced composite) and those that show significant deformation prior to attainment of peak load (such as, the specimens reinforced with the braid and leno-weave).The matrix material is generically more brittle than the fiber and usually has a lower ultimate strain. Thus, as the specimen bends the matrix is likely to develop a series of cracks with the initiation and propagation of cracks depending not just on the type and positioning of the reinforcement, but also on the strain capacity of the neat resin areas. It is thus of use to compute the strain in the composite under flexural load and this can be determined asClick to view the MathML source (3)where D is the midspan toughness of a material can be related to both its ductility and its ultimate strength. This is an important performance characteristic and is often represented in terms of strain energy, U, which represents the work done to cause a deformation. This is essentially the area under the load-deformation curve and can be calculated asClick to view the MathML source (4)where P is the applied load and x is the deformation. In the case of the present investigation, two levels of strain energy are calculated to enable an assessment of the two response types. In the first, strain energy is computed to the deformation level corresponding to peak load (which is also the fracture load for sets A and D). In the case of specimens that show significant inelastic deformation (sets B and C) strain energy is also computed till a point corresponding to a deformation of mm at which point the load shows a 15% drop from the peak. Post-peak response in flexural has earlier been reported by Alander et al. [8].3. ResultsThe application of flexural loading was seen to result in two different macroscopic forms of response. In the case of specimens from sets A and D (reinforced with a unidirectional fabric and unreinforced) failure was catastrophic, in brittle fashion, at peak load, whereas in the case of specimens from sets B and C the attainment of peak load was followed by a very slow decrease in load with increasing displacement, representative of inelastic or plastic, deformation. Typical response curves are shown in Fig. 1 as an Full Size version of this image (24K)Fig. 1. Typical flexural variation in flexural strength (plotted here in terms of stress at peak load) with type of specimen and load introduction method is shown in Fig. 2. The highest strength was achieved by specimens with the braided fabric wherein on average a 125% increase over the unreinforced specimens was attained. Statistical analysis with ANOVA and Tukey's post hoc test revealed that method of load introduction did not affect the results and that further there were no significant differences in overall peak strength results between sets A and B (specimens containing the unidirectional and braided fabrics). Significant differences (p < ) were noted between sets B and C. It is, however, noted that in sets B and C, failure did not occur at the peak load, with load slowly decreasing with increase in midpoint deflection. A comparison of flexural stresses for these systems at peak load and load corresponding to a deflection of mm is shown in Fig. 3. As can be seen the two systems show significant inelastic deformation with drops of only , , and from the peak, emphasizing the stable, ductile and non-catastrophic, post-peak response in these Full Size version of this image (28K)Fig. 2. Flexural strength at peak Full Size version of this image (50K)Fig. 3. Comparison of flexural stresses in specimens having non-catastrophic failure comparison of secant modulus (measured to the peak load) for the different sets is shown in Fig. 4. As can be seen, with the exception of the unidirectional system, the apparent moduli were lower than that of the unreinforced specimens. It is also noted that although the Tukey post hoc tests do not show a significant difference due to orientation of load indenter, the level for the unidirectionals is only compared to 1 for the others. Removal of a single outlier from P1 results in p < indicating a strong effect of orientation of the indenter with the secant modulus being lower with the indenter placed parallel to the fibers, which results in splitting between fibers and uneven fracture with less Full Size version of this image (25K)Fig. 4. Comparison of secant moduli under flexural was noted previously, both the unreinforced samples (set D) and the unidirectional prepreg reinforced specimens (set A) failed in catastrophic fashion at deformation levels significantly less than those at which the other two sets reached the inelastic peak. Since sets B and C did not fracture but showed large deformation with some partial depth cracking through the matrix it is important to be able to compare the levels of strain attained on the tension face using Eq. (3). This comparison is shown in Fig. 5 at the level of peak load (which is the fracture/failure load for sets A and D). While the addition of the unidirectional to the matrix resulted in an average strain of mm/mm which is 50% greater than the capacity of the unreinforced matrix, the addition of the braid and leno-weave resulted in increases of 119 and 126%, respectively, emphasizing the higher capacity of both the UHMW polyethylene fibers and the architectures to hold together without rupture under flexural loading. It should be noted, as a reference, that the strain at the point at which the tests on sets B and C were stopped, at a midpoint deflection of mm, was mm/mm, which represents a 233% increase over the level attained by the unreinforced matrix. The us

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