湿度对手机用纸浆模塑缓冲包装能量吸收特性的影响

基于动态冲击试验,分析了纸浆模塑制品在冲击高度为30 cm、50 cm、80 cm及相对湿度为50%、65%、80%、90%条件下的荷载-位移数据,建立了名义应力-应变曲线和能量吸收曲线。结果表明:冲击高度一定时,随着相对湿度的增大,纸浆模塑制品的名义应力-应变曲线下移,弹性模量、屈曲临界应力明显下降,最佳能量吸收肩点向左下方移动,以RH=50%为基准,RH=65%、80%、90%时的平均第二屈曲临界应力分别下降14%、24%和42%;相对湿度一定时,随着冲击高度的增加,纸浆模塑制品的名义应力-应变曲线上移,弹性模量、屈曲临界应力明显提高,最佳能量吸收肩点向右上方移动,并且冲击高度的影响随相对湿度的增加显著增强;制品在承受冲击荷载时发生两次明显屈曲。     

溶解浆纤维增强缓冲材料的制备及其性能研究

随着日益增长的环保要求,来源于植物源的可降解缓冲包装材料的使用和开发引起了广泛的关注。鉴于此,本文以3种不同植物源的商业溶解浆为原料,基于其在NaOH/尿素水溶液中的溶解,通过模塑成型-再生进行了溶解浆纤维增强缓冲包装材料的制备研究。通过模塑成型材料干燥前后径向与厚度方向尺寸的测量,比较了不同助剂制备的缓冲材料的径向收缩率与厚度方向的收缩率,借助扫描电镜观察了制备的材料的断面形貌,通过拉伸试验绘制应力-应变曲线来分析浆纤维缓冲材料的力学性能,通过振动缓冲性能测试比较了制备的材料的振动缓冲性能。结果表明在7%NaOH/12%尿素水溶液中溶解和在99.5%CH3COOH中再生制备的材料比较柔软、再生容易。另外阔叶木溶解浆纤维制备的缓冲材料较硬,针叶木溶解浆纤维制备的缓冲材料和添加淀粉的竹溶解浆纤维制备的缓冲材料具备一定的振动缓冲性能。添加淀粉制备的竹溶解浆纤维缓冲材料的径向收缩率和厚度方向收缩率都是较小的,且有35%的延伸率。     

应变率对硫化橡胶压缩力学性能的影响

利用分离式霍普金森压杆(SHPB)和材料实验机MTS810对硫化橡胶进行动态和准静态单轴压缩实验,获得硫化橡胶的应力-应变响应曲线,研究了应变率对其压缩力学性能的影响。实验结果表明,硫化橡胶在低应变率时的应变率效应不明显,然而在较高应变率时,应变率对其动态应力-应变关系有明显的影响,弹性模量、屈服应力以及流动应力都随应变率的增大而增大。采用基于应变能函数理论的橡胶本构模型来描述硫化橡胶压缩荷载下的力学行为。数值模拟了硫化橡胶的应力-应变历程,并与实验数据进行比较,结果显示两者吻合良好。     

Effect of cooling rate on the high strain rate properties of boron steel

In this work, the effect of cooling rate on the high strain rate behavior of hardened boron steel was investigated. A furnace was used to austenize boron sheet metal blanks which were then quenched in various media. The four measured cooling rates during the solid state transformation were: 25 (compressed air quench), 45 (compressed air quench), 250 (oil quench) and 2200 °C/s (water quench). Micro-hardness measurements and optical microscopy verified the expected as-quenched microstructure for the various cooling rates. Miniature dog-bone specimens were machined from the quenched blanks and tested in tension at a quasi-static rate, 0.003 s⁻¹ (Instron) and a high rate, 960 s⁻¹ (split Hopkinson tensile bar). The resulting stress vs. strain curves showed that the UTS increased from 1270 MPa to 1430 MPa as strain rate increased for the specimens cooled at 25 °C/s, while the UTS increased from 1615 MPa to 1635 MPa for the specimens cooled at 2200 °C/s. The high rate tests showed increased ductility for the 25, 45 and 250 °C/s specimens, while the specimens cooled at 2200 °C/s showed a slight decrease. The Hollomon hardening curve was fit to the true stress vs. true strain curves and showed that the mechanical response of the high rate tests exhibited a greater rate of hardening prior to fracture than the quasi-static tests. The hardening rate also increased for the specimens quenched at higher cooling rates. Optical micrographs of the fractured specimens showed that the failure mechanism transformed from a ductile-shear mode at the lower cooling rates to a shear mode at the high cooling rates.     

Compression and cushioning characteristics of moulded pulp packaging

Experiments have been carried out to determine the relationship between the geometry of a moulded pulp packaging and the resulting static and dynamic strength. The influence of the shape of the moulded pulp sample has been examined. The shapes were of rounded and squared geometry, with different draft angles, sample heights, volumetric density in order of the level of hotpressing and surface densities. Static strength was examined by compression test. The experimental results show that cylinders, cones and shapes with large roundings produce better compression strength than squared or rectangular products with small roundings. Dynamic strength was found using drop tests to obtain G curves for first impact of the test samples at different conditions. An equation to determine the maximum G value during the drop was found. The equation shows good correlation to the results achieved for small static loads (the left side of the G curves). C/e curves for the different geometries show that the minimum cushion factor attainable for the tested moulded pulp products is approximately 2.0. Copyright © 2000 John Wiley & Sons, Ltd.     

Effect of strain rate on properties of superelastic NiTi thin wires

This study deals with the effect of strain rate on tensile and energy absorbing properties of superelastic NiTi thin wires. It also attempts to gain an understanding of the interplay of the ductile behavior, temperature and strain rate effects, energy storage and cycling. The wires are in austenite condition at room temperature and above. The strain rates imposed during testing range from 0.2 to 180%/min (i.e., 0.06–54 mm/min) corresponding to a frequency of 2.77 × 10⁻⁴ to 0.25 Hz for strain amplitudes of 6%. The corresponding frequency for 8% strain amplitude is 2.08 × 10⁻⁴ to 0.18 Hz. It is shown that NiTi SMAs exhibit ductility at both low and high strain rates. This is also true for the cold worked and heat treated conditions both below M_f and above A_f. During tensile testing the stress-induced martensite (SIM) plateau increases in length and translates upwards with increase in strain rate up to a certain value. Similarly, the onset of elastic yield stress also increases with strain rate. At high strain rates the SIM segment and elastically deformed SIM segment overlap. The SIM formation is not able to cope with the externally imposed higher strain rates. This is also the reason for the reduction of hysteresis loop at the high strain rates as observed in the cyclic tests.

The dissipated strain energy density (E_d) increases with increasing strain rate up to a certain value beyond which the E_d decreases. It is clear that the mean point of the superelastic loop shifts to the right and upwards (higher stress and higher strain region) for cyclic testing with increase in strain rates. However, it shifts to the right and downwards (lower stress/higher strain regime) for both the 6 and 8% strain amplitude cycling at constant strain rate. The stabilization of residual strain and E_d is based on the same underlying mechanism relating to SIM formation and occurs at the same numbers of cycles.     

Study of static cushioning properties and construction of a database for static cushioning properties

The rapid advance of computerization in industrial package design has led to a strong tendency toward CAD/CAM systems using personal computers for quick design and trial manufacturing. New tools based on a database of the cushioning properties of packaging materials will be needed for the design of package cushioning. Using a compression testing machine with computer control, an attempt has been made to construct such a database with registered characteristics for 47 samples of foamed polyethylene, foamed polypropylene and foamed polyethylene-polystyrene. This database offers the following functions and is recorded on floppy disk: (i) calculation of static cushioning properties (value); (ii) print-out of the computed results; (iii) drawing characteristic figures for designing package cushioning; (iv) indicating optimum value of static cushioning properties; (v) additional registration of new samples.     

真空吸滤过程影响纸浆模塑制品质量问题的分析

根据实际生产分析了纸浆模塑制品生产工艺过程影响纸浆模塑产品质量问题产生的原因,并总结出解决这些问题的方法,对实际生产具有指导意义.     

Effect of temperature on the cushioning properties of some foamed plastic materials

Foamed plastics are used to cushion products to protect them from shock and vibration. Design data is in most cases derived from laboratory tests, performed under standard conditions. However, during distribution, most shock and vibration events occur under conditions different from those under which the materials were evaluated. Two commonly used foams in packaging, expanded polyethylene and expanded polystyrene, were used to investigate how changes in temperature affect the performance properties of these materials. The materials were tested for shock and vibration under four different temperatures (?17°C, 3°C, 23°C and 43°C). The results show that the properties of expanded polystyrene were the least influenced and those of expanded polyethylene were the most influenced by changes in temperature. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of strain rate on interlaminar shear properties of carbon/epoxy composites

In this paper, the effect of strain rate on interlaminar shear properties of laminates is studied. The material tested was a T300/5208 carbon/epoxy composite, and the range of strain rates explored was about 10⁻³ − 10³ s⁻¹. The specimens used were designed and optimized by finite element analysis, and the calculations are presented here. One of the specimens permitted the determination of the interlaminar shear modulus, G₁₃, and the other permitted the determination of the interlaminar shear strength, S₁₃. No influence of testing speed on interlaminar properties was observed at low, intermediate and high strain rates. Fracture surfaces were studied by scanning electron microscopy: a slight difference was observed between specimens tested at low and high strain rates.     

疲劳振动效应对瓦楞纸板承载能力与缓冲性能的影响

瓦楞纸板作为产品运输包装的承载与缓冲基础材料,其使用过程中的性能保持性至关重要。运输振动将引起纸板疲劳破损,导致其相应性能的变化。对单瓦楞纸板进行加速度为0.5－2.0g、振动频率为20Hz的疲劳振动试验;进行瓦楞纸板的准静态压缩、跌落冲击试验,测定其承载能力与冲击加速度。结果表明,随着振动次数、振动强度的增加,纸板的承载能力、剩余屈服应力显著降低,缓冲性能下降。在此基础上,基于瓦楞纸板冲击试验数据,分析不同振动次数对瓦楞纸板的冲击最大加速度和缓冲系数的影响,获得了瓦楞纸板冲击最大加速度—静应力—振动次数、缓冲系数—最大应力—振动次数三维关系。研究表明瓦楞纸板存在疲劳破坏效应,研究结果为瓦楞纸板的疲劳缓冲包装设计提供技术依据     

Study of static cushioning properties: Automated data input and reliability test of static cushioning properties

A computer-controlled compression testing machine is used to compile a database of the static cushioning properties of package cushioning materials. Through research into automated data input procedures, so far not developed, a direct transfer program (ZABCON) has been devised, which allows direct access to the disk in which compression test data are stored. Elimination of manual data input has led to simplified and easy construction of a database, and the applied laboratory tests, such as that for determining the relationship between static cushioning properties and compression rate, can be performed quite readily. Also in this report, the application of the static cushioning characteristics of foamed polystyrene in the cushioning package design of dummy goods and the evaluation of its reliability by drop testing are discussed.     

Effect of temperature and strain rate on tensile mechanical properties of ARALL-1 laminates

The combined effect of temperature and strain rate of the mechanical properties for unidirectional 3/2 ARALL^®-1 laminates was studied. In this paper, the effect of strain rates from 0.00083–0.833 min^–1 on tensile behaviour at temperatures up to 250°F (121 °C) has been conducted. It is demonstrated that tensile strength, tensile modulus, and fracture strain are found to depend on temperature and strain rate. However, the effect of strain rates at 75 °F (24 °C) and 180 °F (82 °C) was found to be insignificant except the lowest strain rate at 180 °F. It was also observed that the tensile yield strength decreased as the strain rate decreased. The tensile properties were moderately reduced at high temperatures and were higher at high strain rates than at low strain rates. The temperature effect is more significant than that due to the strain rate. Scanning electron photomicrographs of the fracture surfaces observed in the aramid/epoxy layer of ARALL-1 laminates at the lowest strain rate are shown to be significantly different only at 250 °F (121 °C). But this phenomenon is not obvious when the highest strain rate is employed.     

甘蔗渣缓冲材料的制备及性能

以甘蔗渣碎料为主要原料,利用马铃薯淀粉作胶粘剂,采用模压成型法,以热压时间、热压温度、施胶量、甘蔗渣粒径为研究要素,结合正交实验制备甘蔗渣缓冲材料,并利用SPSS软件及微观形貌分析对其性能进行对比,以得出最优制备方案;进一步研究了甘蔗渣粒径及缓冲材料的密度对其性能的影响。结果表明,上述4个影响因素对缓冲材料各项力学性能影响的显著性有所不同;就材料的最小缓冲系数而言,当热压时间为50s,热压温度为120℃,施胶量为6%时,材料的综合性能最佳;材料的密度为170~190kg/m3量级最为适宜;甘蔗渣粒径为8~14目时,缓冲材料最小缓冲系数达到最小值。     

Effect of aging on high strain rate and high temperature properties of 7075 aluminium alloy

Abstract

The high strain rate and high temperature properties of as cast and aged 7075 aluminium alloy were examined by metallographic observation and by means of a split Hopkinson bar test at temperatures between 25 and 300°C and at strain rates of 1·3 × 10³ and 3·1 × 10³ s^-1. The effect of aging, as well as strain rate and temperature, on the dynamic mechanical response, microstructure evolution, and fracture characteristics are presented. The compressive stress–strain response of as cast and aged 7075 alloy is found to depend strongly on both the applied strain rate and the test temperature. However, the aged material is generally found to be stronger than the as cast material. The work hardening rate is seen to decrease with increasing strain, strain rate, and temperature, and its value is higher in the aged material than in the as cast material. Microscopic observation shows that aging, strain rate, and temperature have a significant influence on the microstructural evolution and the changes in grain morphologies. The average grain size can be expressed by a Hall–Petch type relationship after impact deformation. Fracture surface examination revealed that a high strain rate favours the formation of deformed shear bands that are precursors to crack formation and fracture. The aged material has a better ductility owing to the higher percentage of transgranular fracture and an increased density of microdimples.     

Effect of drawing strain rate on microstructure and mechanical properties of cold-drawn pearlitic steel wires

Journal of Materials Science - Microstructural evolution of cold-drawn pearlitic steel wires (CPWs) with different drawing strain rates and their effects on mechanical properties of CPWs were...