Studies on the Reduction of Coefficient of Variation: A Case Study

In a spinning mill, yarn is the final product. Linear density expressed in terms of count is one of the important characteristics of yarn. Because variability of textile strands increases as the linear density increases, the variability in the count is often measured in terms of coefficient of variation (CV)%. The yarn with a high CV% of count leads to a higher end breakage rate during the spinning and subsequent weaving/knitting operations, and consequently, results in lesser productivity and poorer appearance quality of the woven/knitted fabric. When this woven/knitted fabric is dyed, uneven shades are generated. Because the production of yarn involves processing of raw cotton in multimachines at multistages, possible sources that lead to a high CV% of count are many. Enrick's (1960) analysis procedure, which is based on the modification of the range method for analysis of variance, is used conventionally for detecting the stages where excessive “between-machine” differences are present. When the CV% of count is inflated due to the generation of systematic variation in any machine or introduction of high variability by any machine, this inflation remains undetected when using Enrick's procedure. The case study presented here demonstrates that a step-by-step analysis of linear densities of different stage-outputs starting from yarn to card sliver, using appropriate nested design models along with Duncan's multiple range test, is very useful in detecting all possible sources of a high CV% of count of yarn.     

田口法研究3Y-TZP/TiN导电陶瓷材料最佳化制程

实验用田口法研究了添加30wt%氮化钛的钇稳定氧化锆基陶瓷材料(3Y-TZP/TiN)制造工艺. 选择烧结方式、TiN粉末振荡时间、第一阶段保温时间及第二阶段烧结温度四个工艺参数作为控制因子, 设计L₉正交表进行实验规划. 烧结后, 检测试片断裂韧性、抗弯强度、硬度、相对密度及电阻值. 最后通过变异数分析找出最佳参数, 再进行实验验证. 本研究得到的最佳化烧结工艺为: TiN粉末振动8 h, 采用两步烧结法, 第一阶段烧结温度1450℃, 不保温, 第二阶段烧结温度1150℃, 保温20 h. 结果显示, 采用该工艺得到了抗弯强度平均值为736.75 MPa、断裂韧性为7.545 MPa·m^1/2的氧化锆基导电陶瓷材料. 研究发现, 第一阶段保温时间对断裂韧性的影响程度最大, 其次依次为烧结方式、TiN粒径大小及第二阶段保温温度. 断裂韧性的微结构影响因子为四方相与单斜相数量的比值, 当此值达到最高时, 断裂韧性也达到最高值为9.275 MPa·m^1/2. 另外, 添加30wt% TiN的氧化锆电阻率平均值为3.26 m?·cm, 可以进行电火花加工.     

Effects of inter-fibre spacing and matrix cracks on stress amplification factors in carbon-fibre/epoxy matrix composites. Part I: planar array of fibres

When the loading on a composite is sufficient to cause fracture of an individual fibre, the resulting stress amplification in the adjacent intact fibres may be large enough to cause failure of these fibres. In this work, 3D elasto-plastic finite element analysis was used to investigate the effect of inter-fibre spacing on the stress amplification factor in a composite comprising a planar array of fibres. A Progressional Approach was used in the FE analysis to simulate the constituent non-linear processes associated with the generation of thermal residual stresses from fabrication, the fibre fracture event and the subsequent initiation and propagation of conical matrix cracks induced with incremental tensile loading. As the inter-fibre spacing increases, the effect of fibre fracture on the stress distribution in the neighbouring intact fibres is reduced, whereas the effect on the matrix material is increased, thereby inducing localised yielding. The presence of a conical-shaped matrix crack was found to increase both the stress amplification factor and the positively affected length in neighbouring fibres. For a large inter-fibre spacing, a longer matrix crack is required to obtain good agreement with LRS measurements of fibre stress.     

Studies on the development of aluminium alloy–mild steel reinforced composite

With a view to developing a new metal–metal cast composite material as a possible substitute for ferrous materials in wear resistant applications, Al alloy (LM11) is reinforced with mild steel (ms) wires and it is heat treated to get ‘reaction interface’ (RI). Microhardness, tensile properties and wear characteristics of the matrix, as-cast and heat treated composites have been determined. While microhardness of the composite showed variation from 150 to 45 VHN across the interface in the as-cast composite, annealed (500–525°C) composite showed a microhardness of 350–420 VHN at the interface indicating the effectiveness of the heat treatment. It is seen that the % improvement in wear resistance increased with increase in number of wires when embedded in the aluminium alloy matrix. Further imrpovement of about 30% was observed when heat treated at 500°C for 15 h. These results have been discussed in terms of wetting between ms wires and the matrix, particularly the increase of hardness and tensile strength to the formation of ‘reaction interface’ due to annealing. The width of the interface increased with annealing time and temperature and the kinetics of reaction followed logarithmic and parabolic growth rate. The activation energy for the formation of intermetallics constituting the reaction interface is found to be 20.7 KJ mol⁻¹. From the measured hardness and ultimate tensile strength of the constituents and composites an empirical relation was deduced.     

The influence of nano/micro hybrid structure on the mechanical and self-sensing properties of carbon nanotube-microparticle reinforced epoxy matrix composite

Nano/micrometer hybrids are prepared by chemical vapor deposition growth of carbon nanotubes (CNTs) on SiC, Al₂O₃ and graphene nanoplatelet (GNP). The mechanical and self-sensing behaviors of the hybrids reinforced epoxy composites are found to be highly dependent on CNT aspect ratio (AR), organization and substrates. The CNT–GNP hybrids exhibit the most significant reinforcing effectiveness, among the three hybrids with AR1200. During tensile loading, the in situ electrical resistance of the CNT–GNP/epoxy and the CNT–SiC/epoxy composites gradually increases to a maximum value and then decreases, which is remarkably different from the monotonic increase in the CNT–Al₂O₃/epoxy composites. However, the CNT–Al₂O₃ with increased AR ⩾ 2000 endows the similar resistance change as the other two hybrids. Besides, when AR < 3200, the tensile modulus and strength of the CNT–Al₂O₃/epoxy composites gradually increase with AR. The interrelationship between the hybrid structure and the mechanical and self-sensing behaviors of the composites are analyzed.     

The influence of thermal history on the mechanical properties of poly(ether ether ketone) matrix composite materials

The purpose of this study is to provide insight into the microstructural factors that affect the flexural fatigue performance of carbon-fibre-reinforced poly(ether ehter ketone) (PEEK) composites. Specifically, the effect of the degree of crystallinity on the mechanical properties is examined at two crystallinity levels of the as-received composites (35%) and of quenched composites (10%). Higher static flexural strength and modulus as well as longer fatigue life are observed for the higher crystallinity level. By varying the loading angle with respect to the fibre direction it is shown that the crystallinity effect is not matrix dependent alone. Rather, a strong effect is evident in the fibre direction, which is attributed to the influence of the transcrystalline layer formed on the fibre surface in the high-crystallinity material. As a result, the longitudinal fatigue life at 1·7GPa of the 35% crystallinity material is three orders of magnitude higher than that of the 10% crystallinity composite.     

Querschnittseinfluss beim Zugversuch von siliziertem kohlenstoffkurzfaserverstärktem Kohlenstoff (C/C‐SiC)

On the influence of cross section in tensile tests of siliconized short carbon fibre reinforced carbon (C/C‐SiC) This study deals with the mechanical testing of a carbon short fibre reinforced ceramic. For this material group, which has already been successfully used in several applications, no valid testing specifications are existing at present. This is one of the reasons why manufacturers and research institutes often make use of test standards for monolithic or composite materials. In these tests, sample cross sections and testing volumes are choosen freely or on the basis of a standard and are accordingly adapted by an appropriate factor. This approach can lead to misinterpretations. Because of the broad variety in the different kinds of fibre reinforced ceramics, this study examines the influence of cross sections in tensile tests in an examplary study on a siliconized short carbon fibre reinforced carbon of the Schunk Kohlenstofftechnik GmbH labeled FU2952/1P77. In order to verify the test results, the fracture surfaces will be examined by means of incident light photography and scanning electron microscopy (SEM).     

基于广义置信区间的测量系统能力比较

研究了测量系统分析中对测量同一产品质量特性的两个测量系统能力的比较方法。基于广义推断法,提出了一种比较两个测量系统能力的方法。通过重复性与再现性（R&R）试验研究,利用广义推断法对两个测量系统能力的比较指数建立相应的广义置信区间,并进行计算机仿真。结果表明,基于广义置信区间的方法,可以有效地比较两个测量系统的能力。     

Effect of microwave irradiation on carbon fiber/epoxy resin composite fabricated by vacuum assisted resin transfer molding

The effects of microwave irradiation for resin-curing of carbon fiber/epoxy resin composite (CFRTS), which was fabricated by vacuum-assisted resin transfer molding (VARTM) method, were investigated at 2.45 GHz frequency. The mechanical properties of CFRTS cured by microwave irradiation for 20 min at 120 °C were similar as compared to the conventional oven for 300 min at 120 °C. Moreover, the CFRTS irradiated by microwave had better adherence property between fiber and resin as compared to conventional oven at same resin-curing time. From the relation between resin-curing and mechanical property, it was found that the curing rate of microwave-irradiated CFRTS was 15 times faster as compared to conventional heating. Furthermore, the activation energies for resin-curing reaction on conventional- and microwave-cured CFRTS were estimated to be 2.7 and 1.3 × 10⁴ J/mol, respectively. The resin-curing reaction in CFRTS prepared by VARTM method was significantly promoted by microwave irradiation at short time.     

Phases analysis and impact of phases on fracture mechanism of AZ61‐SiC composite

Phase composition of AZ61‐SiC composite with 5 wt.% of nanosized silicon carbide reinforcement was analysed and failure mechanism by in situ tensile test in scanning electron microscope was observed. Microstructure of the experimental materials was heterogeneous with grain size of 15 μm. Based on the quantitative analysis of composite, besides, silicon carbide strengthened particles added externally into the matrix magnesium silicide, magnesium oxide, and aluminium/manganese particles formed in situ were found in the matrix. In situ tensile test in scanning electron microscope has shown that reinforcing particles substantially influenced failure mechanism. Large, brittle magnesium silicide particles (size of 40 μm–50 μm) cracked during tensile deformation and at the same time, as a result of different physical properties, decohesion of the matrix and smaller aluminium/manganese, silicon carbide and magnesium oxide particles (size of 5 μm–10 μm, 10 μm and 50 nm respectively) occurred. Reinforcing particles and brittle secondary phases driven micro voids and their coalescence was found as a major cause of large cracks formation. Subsequently the increase of stress caused the cracks propagation by the coalescence of fractured particles and decohesively release smaller dispersed particles. The fracture propagated at approximately 90° angle to the direction of the tensile load direction. Fracture surface had feature of transcrystalline and intercrystalline failure.     

六亚甲基二异氰酸酯(HDI)交联壳聚糖与三甲基-烯氯化铵接枝共聚物/聚丙烯腈复合纳滤膜的研究

以壳聚糖与三甲基-烯氯化铵共聚物的水溶液为铸膜液,涂敷在聚丙烯腈超滤膜上,以六亚甲基二异氰酸酯为交联剂,制备了壳聚糖与三甲基一烯基氯化铵共聚物复合阳离子型纳滤膜.着重讨论了交联剂浓度、交联时间、干燥时间等因素的影响,采用单因素实验法确定了最佳的制膜条件:以0.75%(质量分数)的壳聚糖与三甲基-烯氯化铵共聚物水溶液为铸膜液,在50℃下干燥2h.在乙醇、HDI的质量比为50:0.32交联体系中,50℃水浴浸泡交联21h,50℃下热处30min.通过电镜扫描对膜结构进行观察.膜的截留分子量大约为900Da.并且,对该复合膜的性能进行了测试,分别探索了操作压力、料液浓度、料液类型等因素与膜性能的关系.在20℃,流速为30L/h,操作压力为1.2MPa时,对2000mg/L MgCl2、NaCl、MgSO4、CaCl2、Na2SO4、KCl、K2SO4的截留率分别为95.6%、66.4%、80.8%、95.4%、30.7%、53.7%、23.8%;通量分别为6.73、7.35、6.43、6.73、6.12、6.12、6.43L/(h·m-2).对不同类型无机盐的截留顺序为MgCl2≈CaCl2＞ MgSO4＞NaCl＞KCl＞Na2SO4＞K2SO4,呈现阳离子型复合纳滤膜的截留特征.流动电位曲线进一步说明了该复合膜的荷正电性,其电压渗系数β为6.8mV/MPa.     

An analysis of synergistic and antagonistic behavior during BTEX removal in batch system using response surface methodology

The removal of benzene, toluene, ethylbenzene and xylene (BTEX) as quaternary mixtures were studied in batch systems using a well-defined mixed microbial culture. The synergistic and antagonistic effects of total BTEX removal (BTEXT-RE) due to the presence of mixed substrate was evaluated through experiments designed by response surface methodology (RSM). The low and high concentrations of individual BTEX were 15 and 75 mg l(-1), respectively. The results showed that, increasing the concentration of xylene increased the cumulative BTEX removal (BTEXT-RE), however the reverse occurred when benzene concentrations were increased from low to high levels. A mixed response of increasing and decreasing trend in the BTEXT-RE value was observed when either of toluene or ethylbenzene concentration was increased. When the concentrations of individual BTEX compounds were 30 mg l(-1), the BTEXT-RE was about 58%. Complete BTEXT-RE was achieved at optimal BTEX concentrations of 48.1, 45.6, 49.3 and 56.6 mg l(-1). The RSM approach was found efficient in explaining the main, squared and interaction effects among individual BTEX concentrations on the BTEXT-RE in a more statistically meaningful way.     

Multivariate analysis of anionic, cationic and nonionic textile surfactant degradation with the H(2)O(2)/UV-C process by using the capabilities of response surface methodology

Anionic, cationic and nonionic surfactants being frequently employed in the textile preparation process were subjected to H(2)O(2)/UV-C treatment. As a consequence of the considerable number of parameters affecting the H(2)O(2)/UV-C process, an experimental design methodology was used to mathematically describe and optimize the single and combined influences of the critical process variables treatment time, initial H(2)O(2)concentration and chemical oxygen demand (COD) on parent pollutant (surfactant) as well as organic carbon (COD and total organic carbon (TOC)) removal efficiencies. Multivariate analysis was based on two different photochemical treatment targets; (i) full oxidation/complete treatment of the surfactants or, alternatively, (ii) partial oxidation/pretreatment of the surfactants to comply with the legislative discharge requirements. According to the established polynomial regression models, the process independent variables "treatment time" (exerting a positive effect) and "initial COD content" (exerting a negative effect) played more significant roles in surfactant photodegradation than the process variable "initial H(2)O(2) concentration" under the studied experimental conditions.