集聚纱与非集聚纱的轴向应变及其对纱线拉伸性能的影响

通过试验重点研究了轴向应变对集聚纱拉伸性能的影响。拉伸性能主要涉及断裂强度、断裂伸长和断裂功。选择不同的应变速率和纱线夹持长度,对9.7 tex集聚纱和非集聚纱进行拉伸测试,然后根据Meredith试验过程绘制不同应变速率和夹持长度条件下各自的负荷-伸长曲线,同时测量各曲线三个区域的斜率。测试结果表明：两种9.7 tex的纱线（集聚纱和非集聚纱）随着应变速率的增加,断裂强度均增加,但当断裂伸长增加到一定程度,且在较高应变速率下,断裂强度有所下降;两种纱线随着夹持长度的增加,断裂强度和断裂伸长均降低;两种纱线的斜率随着应变速率的增加均增加,但随着夹持长度的增加而下降。试验还发现,非集聚纱的斜率变化较大,而集聚纱的斜率变化较小。     

非织造布购物袋接缝强力测试影响因素探讨

通过设定不同的试样宽度、拉伸速率和隔距尺寸测试纺粘法PP非织造布购物袋接缝强力。对测试结果进行分析得知,非织造布购物袋的接缝强力随着试样宽度的增加而线性增加,拉伸速率和隔距尺寸对接缝强力测试结果的影响不显著。     

锡林速度对盖板花纤维长度分布的影响

研究了锡林速度对盖板花纤维长度分布的影响。用Premier a Qura棉结和短纤维测试仪对4档锡林速度条件下加工生成的盖板花进行了长度检测,分析了不同锡林速度下盖板花纤维长度分布情况。结果表明:锡林速度变化对盖板花纤维长度分布影响较大。随着锡林速度提高,盖板花中12 mm以下短纤维含量有增加的趋势;从盖板花纤维长度分布看,4种锡林速度以450 r/min最利于对盖板花纤维长度分布的改善,该速度下盖板花中18 mm以下纤维所占比例明显高于其他几种速度。认为通过纤维长度分布来评价纤维的分梳情况比只用长度指标更全面、更准确。     

编织结构玻璃长丝缝合线的打结强度

针对玻璃纤维丝束在纺织预制件或预浸料的缝合过程中易发生断裂的情况,设计了二维管状编织结构的玻璃纤维缝合线。采用Instron电子万能试验机对不同编织工艺参数的缝合线试样分别进行了loop结和knot结的拉伸强度测试,分析了拉伸断裂的机制和破坏模式。结果表明：编织结构玻璃长丝缝合线的打结强度和断裂伸长率明显高于玻璃丝束;花节长度是影响打结性能的主要因素;试样在试验过程中受剪切和拉力共同作用,经历伸直-受力-断裂几个阶段,试样断口基本平齐。     

Prediction of spun yarn strength at different gage lengths

In this article, the influence of tensile tester gage length on ring, rotor and air-jet spun yarns tenacity and its coefficient of variation have been investigated. A statistical model has been presented that correlates yarn tenacity and coefficient of variation of yarn tenacity to gage length. The model is based on Peirce model and assuming the three-parameter Weibull distribution of yarn strength values. A reasonable agreement has been shown between the experimental and predicted values. The model successfully captured the change in yarn strength and its coefficient of variation at different gage lengths. Results showed that at longer gage lengths, yarn strength decreases and its coefficient of variation decreases as well.     

Die Rohdichteverteilung und deren feuchteabhängige Änderung bei astiger fichte im hinblick auf die maschinelle Holzsortierung

For the machine grading of timber by isotopic-radiation the difference in density between sections with and without knots is being used as a criterion to evaluate the knot ratio. The precondition for the general use of this method, even for wood with varying moisture contents would be to prove that there are no changes in density relationship at least up to fiber saturation. For determining the relationship and density changes in spruce, with and without knots, comprehensive investigation on 230 test groups (1600 specimens) were carried out. Evaluation of results led to the conclusion that a reliable differentiation regarding the criterion “knot ratio” is possible for moisture content up to 30%, independent of the initial data of the timber to be graded.     

EFFECTS OF PRE-RIGOR TENSION ON TENDERNESS OF INTACT BOVINE AND OVINE MUSCLE

Mechanical and weighted methods of applying pre-rigor tension to longissimus muscle of ovine and bovine carcasses conventionally hung by a hind shank were studied. The effect of tensioning of carcasses by adding 4.5 kg weights or mechanically stretching the back 5% in length was significant (P < 0.01) and as effective as greater forces in decreasing shear force values, decreasing fiber diameters and increasing sarcomere lengths. Chops and steaks from tensioned carcasses at 48 hr postmortem were as tender as those from non-tensioned carcasses which had been aged 168–240 hr. Further aging of longissimus muscle of tensioned carcasses continued to decrease shear force values at approximately the same rate at which shear force was decreasing in nontensioned carcasses. The pre-rigor tension was also effective in reducing animal-to-animal tenderness variability.     

Methodological Aspects of Determining Apple Mechanical Properties During Impact

The influence of cylindrical sizes of samples and velocity of impact on its course and strength parameters for the “Braeburn” variety apples was studied. Three sample lengths of 17, 19, and 21 mm, three diameters of 10, 15, and 20 mm and four impact velocities of 0.25, 0.5, 0.75, and 1 ms^–1 were applied. Failure stress and strain, impact energy, absorbed energy as well as tissue stiffness and toughness were determined as dependent variables. The influence of the sample diameter on maximum force response, impact energy, absorbed energy, and tissue stiffness was studied. The other independent variables: Sample length and impact velocity did not show significant influence on the strength parameters of the apple tissue. The shock wave speed in the apple tissue was independent of both sample sizes and impact velocity. Its mean value amounted to 292 ms^–1. Under the experimental conditions the mean value of the absorbed energy contribution to the impact energy amounted to 9.9%. The experiment confirmed importance of a critical stress criterion as regards cylindrical samples of apples under impact conditions.     

19—AN APPLICATION OF MINI-COMPUTERS TO THE OPTIMIZATION OF THE OPEN-END-SPINNING PROCESS PART XI: THE OPTIMIZATION OF THE OPENING-ROLLER SPEED AND TWIST FOR PROCESSING CONDITIONS REMOTE FROM THE OPTIMUM DURING THE ROTOR-SPINNING OF COTTON YARNS

The optimum values for both the opening-roller speed and the yarn twist, in operating with near-extreme values of both the total draft and the rotor speed, are studied. These values of draft and speed are, nevertheless, not uncommon in industry. For a total draft of 173 and a rotor speed of 45 000 r/min, and with a Süssen Rotorbox machine, it was found that the optimum values of yarn twist and opening-roller speed did not coincide with each other when either the yarn regularity or tenacity was considered as the most important parameter, a phenomenon that had, in fact, been observed earlier when all the operating parameters were optimized. In this instance, the best quality indices are obtained for opening-roller speeds above 6000 r/min and twist multipliers, a, of about 160 for a 23.57-tex yarn (N _e = 25).     

Effect of pre-crack length on Mode I fracture toughness of 3-D angle-interlock woven composites from finite element analyses

Fracture toughness is a key factor to design impact behaviors of composite materials. This paper reports the influence of pre-crack length on Mode I fracture toughness of 3-D angle-interlock woven composites. Double cantilever beam specimens with different pre-crack lengths were tested to obtain load-displacement curves and strain energy release rates. A finite element analysis model at microstructure level was established to reveal the fracture damage development and stress distribution in the specimens. We found that the fracture toughness decreases with increase in pre-crack length. The higher pre-crack length resulted in increased stress concentration at crack tip position and the enhanced crack propagation. The higher strength through-thickness yarns are recommended for improving fracture toughness.     

New test methods to evaluate the performance of dermatological braided sutures from both the doctor and the patient sides

Test methods and instrumentations to measure suture tensile performances have been limited to single‐pull to failure and knot‐pull strength. Though useful, these tests do not thoroughly represent the stresses that sutures experience during wound healing. This paper proposes new test methods to evaluate the performance of dermatological sutures using slippage ratio and recovery deformation based on a realistic representation of suture geometry in wounds. For demonstration purposes, we compared three dermatological knots: square, surgeon’s square, and surgeon’s granny. Our results confirmed that the knot design and the generated internal forces in the knot led to significant change in suture behavior during the tying and healing process. Suture performance depended greatly on the intensity of internal forces and the ability of knot packing. Among the studied knots, the square knot had the lowest slippage ratio because it showed the best aptitude to tightening, while the surgeon’s knot exhibited the highest deformation recovery due to its lower locking ability.     

A study on siro-, solo-, compact-, and conventional ring-spun yarns. Part II: yarn strength with relation to physical and structural properties of yarns

The strength of siro-, solo-, compact-, and conventional ring-spun yarns has been examined with reference to yarn migration parameters, spinning-in-coefficient, number of broken fibers, and yarn hairiness. The measured results are presented in the forms of diagrams and tables. Results reveal that at various levels of gage length and strain rate, siro-spun yarns exhibit the highest tenacity, followed by compact-spun yarns, solo-spun yarns, and conventional ring-spun yarns. Analysis of the results demonstrate that the higher tenacity values of siro-spun yarns can be attributed to the higher mean fiber position, higher migration factor, greater proportion of broken fibers, and lower hairiness. It is also found that the strength of yarns to a considerable extent is governed by yarn structure, gage length, and strain rate.     

Asymmetric tensioning of circular saws

The most frequently used tensioning methods are hammering and roll tensioning. The effectiveness of hammering depends heavily on the skill of the saw filer. Roll tensioning is a well understood technique that yields increases in some natural frequencies while decreasing others. Thus, an optimal tensioning exists beyond which further rolling buckles the saw into a “dish” shape. This paper introduces a new tensioning method in which the natural frequencies associated with all the saw vibration modes are increased simultaneously. An eccentric hole is introduced into the saw, and a uniform normal pressure is applied to the face of the hole. The natural frequencies increase monotonically with increased pressure, and the magnitude of the shifts increase with the introduction of additional stressed holes. Hole eccentricity affects which natural frequencies are altered most, so the tensioning can be directed towards optimal increases in certain vibration modes. The predicted increases in the natural frequencies associated with the potentially unstable modes are limited only by the restrictions of classical plate theory and loading within unstable modes are limited only by the restrictions of classical plate theory and loading within the elastic limit of the saw.     

重定量条件下提高成纱质量的工艺实践

探讨重定量对细纱牵伸的影响与工艺控制措施。通过工艺对比试验表明:重定量对细纱牵伸的影响主要表现在纤维移距偏差增大、控制作用相对减弱、纤维变速点分散、握持力与牵伸力不匹配。可采取小前区隔距、大后区隔距、新型下销纵向强控制、压力棒隔距块稳定变速点、小钳口紧控制等工艺措施;采用高弹性胶辊重加压工艺,选用C型罗拉座及气压加压摇架等器材,可确保正常牵伸。指出:只有稳定和提高成纱质量,才能促进重定量工艺的推广与应用。     

Methodology to Determine Destruction of Bacterial Spores during Extrusion Cooking

A methodology was developed for determining destruction of bacterial spores during extrusion cooking in a single screw extruder. Procedures were developed for estimating processing time at different screw speeds and calculation of “D-” and “z-values.” The proposed methodology evaluated destruction of Bacillus globigii spores in 18% moisture corn/ soybean mixture (70/30%, w/w). “D-value” expressed on the basis of average time at mass temperature >95°C during extrusion was the most conservative estimate of spore sensitivity. Times ranged from 1.7 sec at 115°C to 6.6 sec at 100°C maximum mass temperatures. These “D-values” resulted in a “z-value” of 25.3°C., similar to that reported for the same strain with dry heat.     

涤纶仿毛长丝弯曲性能测试因素分析

为模拟涤纶仿毛长丝在实际织造条件下抗弯曲性能,对4种规格涤纶仿毛长丝的打结位置、拉伸速度和夹持距离等打结参数对其打结断裂强力和打结断裂伸长率影响进行探究。实验结果表明:长丝打结后的断裂强力和断裂伸长率比未打结状态下小,说明长丝弯曲后力学性能变差;打结位置偏离中心位置越远,打结断裂强力越小,而打结位置越接近拉伸下夹头位置,打结断裂伸长率越大;长丝打结后断裂强力和断裂伸长率遵循"弱环定律";打结断裂强力随长丝细度的增大而增大,但打结断裂伸长率与细度无关。     

Re-examination of the linear glutenin hypothesis

The hypothesis that glutenin molecules consist of polypeptide chains joined by SS bonds into linear concatenations, instead of into branching giant molecules, is further examined. The concept that secondary forces can build up sequentially to produce appreciable tension in the molecules appears to fit the facts better than the idea that entangled molecules behave like a knot, which predicts a relation between tenacity and mol.wt. not observed for other high polymers. Work hardening arises because orientation makes the most effective use of secondary forces, the molecules being aligned so that they overlap by substantial fractions of their lengths. SS interchange in dough not only relieves stress but controls the average length of concatenations. Viscous flow depends predominantly on molecular slip, but is assisted by mechanical fission and SS interchange. In a resting dough mechanical scission is absent and SS interchange makes a relatively greater contribution to stress relaxation. Mechanical scission will not occur in terminal segments of concatenations. In an overworked dough, the length of many concatenations is at least halved by mechanical scission, greatly reducing the resistance. The predicted level of SH groups produced by mechanical fission is of a similar order to an experimental value quoted in the literature.     

梳棉机后固定盖板隔距对纤维长度分布的影响

为探讨后固定盖板隔距对纤维长度分布的影响,用AFIS单纤维测试仪对不同道夫速度、刺辊速度和后固定盖板隔距所加工生条进行了纤维长度检测.结果显示,无论产量高低,隔距过小对长纤维损伤都比较严重;当产量较低时,以0.5 mm隔距方案对生条中纤维长度分布较为有利;当产量较高时,以0.75 mm～1.0mm固定盖板隔距方案对生条中纤维长度分布比较有利.     

83.3 tex花式变支数纱的拉伸性能

采用瑞士AmslerTex公司生产的花式纱装置,通过改变工艺参数,例如锭子速度、钢丝圈质量和合股捻系数等,可以在环锭细纱机上生产不同性能的83.3 tex花式股线纱.这些性能包括纱线强度、断裂强力、断裂伸长率,以及断裂功等.其中,纱线的强度和断裂强力随着钢丝圈质量的增加而增大.断裂功最大值则出现在锭速较低和钢丝圈质量较小时,而选定的合股捻系数对纱线性能的影响并不显著.     

Bruchenergien,kritische Energiefreisetzungsraten und Bruchzähigkeiten von Fichte bei Zugbeanspruchung senkrecht zur Faserrichtung

It is reported on Mode I fracture energyG _f, critical strain energy release rateG _c and fracture toughnessK _c of spruce in RL-crack system. The investigations were performed with special SENB specimens acc. to a CIB W18A draft standard. For determination of size effects geometrically similar specimens of significant different sizes were tested; the cross-sectional depthd varied from 10 to 320 mm and notch length was constant 0,6d. All “tension perpendicular to grain volumes” were cut from two boards with similar mean densities of about 460 kg/m³. The paper first deals with some general aspects of related energy termsG _f resp.G _c and then gives finite element results for normalized strain energy release rates and stress intensity factors of the specific orthotropic specimen. The experimental results can be summarized as follows: Fracture energyG _f is quite independent of initial crack length and counts in mean 280 N/m; the 5th percentile value due to fitted 3parameter Weibull distribution is 180 N/m and thus about 30% lower as given implicitly in Eurocode 5 for respective density. For density dependency in the range of about 420 to 480 kg/m³ the linear relationG _f≈0,62 ρ₁₂ was found. Critical strain energy release rateG _c increases degressively with specimen depth resp. initial crack length. Compared toG _f,G _c is roughly 25% lower up to crack lengths of about 60 mm and is then of similar quantity asG _f. Fracture toughnessK _c alikeG _f, was found to be quite independent of initial crack length; for mean and characteristic values 440 resp. 280 kN/√m³ were received.