黄麻纤维束力学性能的尺寸和应变率效应

为了探究黄麻纤维束的尺寸效应和应变率敏感性,利用C43电子式万能试验机和CEAST 9340落锤试验冲击系统分别在静动载条件下对黄麻纤维束进行测试,获得了杨氏模量、强度、峰值应变和韧性随标距和应变率的变化关系静载试验在1/600s-1应变率条件下进行,测试了6组不同标距(25、50、100、150、200和300mm)的试件;动载试验以应变率为变量,在4组不同的应变率(40、80、120和160s-1)条件下进行了测试,试件标距均为25mm。测试结果表明:随着试件标距增大,杨氏模量初始增大,当标距大于100mm时趋于稳定;强度、峰值应变和韧性均减小。随着应变率增大,杨氏模量和强度均增大;峰值应变初始减小后趋于稳定;韧性先减小后增大。鉴于植物纤维束材料较大的性能离散性,采用Weibull分布对试验数据进行拟合,获得了黄麻纤维束强度在不同试验条件(标距和应变率)下的分布规律。     

动态拉伸载荷下应变率和温度对Kevlar 49芳纶纤维布增强环氧树脂复合材料力学性能的影响

为研究Kevlar 49芳纶纤维布增强环氧树脂复合材料在中等应变率和不同温度耦合作用下的力学响应和断裂行为,首先,利用MTS液压伺服高速机在不同初始应变率(25、50、100、200 s-1)和温度(-25、0、25、50、100℃)下对芳纶纤维增强复合材料(AFRP)进行单向动态拉伸测试;然后,采用Weibull分析模型量化了拉伸强度在不同应变率和温度下的离散程度。结果表明:在相同温度(25℃)下,随着应变率的增加,弹性模量和拉伸强度均先增大(初始应变率介于25~50 s-1范围内)后减小(初始应变率介于50~200 s-1范围内),极限应变则呈现出相反的变化趋势,而韧性随应变率的变化幅度不大;在相同初始应变率(25 s-1)下,与在25℃下的情况相比,温度的升高或降低均会造成弹性模量的降低,在温度为100℃时,极限应变显著增加,而拉伸强度和韧性均不会随温度的变化而发生明显改变。对AFRP断裂形态进行的对比分析表明不同试验条件下AFRP的断裂形态基本相同,均呈现出较为平整的断裂面。所得结论可为AFRP在极端载荷和环境作用下的理论研究和应用提供依据。      

Kevlar~? 29纤维多尺度力学行为的试验研究和有限元模拟

利用MTS万能试验机和MTI微型拉伸试验机分别研究了Kevlar?29纤维束与纤维单丝在不同标距下(纤维束:25 mm、50 mm、100 mm、150 mm、00 mm和300 mm;纤维单丝:12.5 mm、25 mm和40 mm)的力学性能。结果表明,Kevlar?29的拉伸强度随着结构尺度(从纤维单丝到纤维束)的增加而降低;标距对Kevlar?29纤维单丝力学性能的影响并不显著;但对纤维束而言,拉伸强度随着标距的增加而降低,呈明显的尺寸效应。利用Weibull模型进行统计分析,量化了不同标距下纤维单丝拉伸强度的随机变化程度。这些统计参数将用于有限元模型以模拟静载下Kevlar?29纤维束的拉伸行为。该模型基于ANSYS中的用户自定义子程序(USERMAT),并考虑了纤维单丝的随机破坏。模型的预测结果与试验结果相吻合,并讨论了关键参数对模拟结果的影响。     

纤维束的冲击拉伸实验研究

本文所述实验采用岛津DT-5000型万能实验机和自行研制的摆锤式杆-杆型冲击拉伸试验装置对玻璃纤维,Kevlar49及碳纤维束做了应变率从10-4到 102 s-1量级之间的冲击拉伸实验。首次得到纤维束在高应变率下的拉伸应力应变曲线。结果表明:玻璃纤维的强度,极限应变以及临界应变能密度对应变率非常敏感,弹性模量也随应变率的升高而增加。Kevlar49纤维对应变率不太敏感,而碳纤维的性能则对应变率不敏感。     

不同标距下CVD钨芯SiC纤维强度的Weibull分布

对用冷壁气相沉积制备的CVD钨芯SiC纤维的抗拉强度分布进行了研究.用环氧树脂将纤维粘结在纸夹中进行拉伸,标距分别为10mm,25mm和50mm.结果表明,CVD钨芯SiC纤维室温下的强度服从Weibull分布.10mm,25mm和50mm标距下的Weibull模数分别为6.03,5.23和4.36,Weibull模数随试样标距增大而减小.纤维强度平均值在标距长度为25mm时最大,50mm时次之,10mm时最小.     

Kevlar49单丝和单束的随机破坏及有限元模拟

为研究不同尺度下Kevlar49单丝(微观)和单束(细观)的拉伸力学性能,首先,分别采用MTI微型拉伸试验机和MTS微机控制电子万能试验机对纤维丝和纤维束进行了单向拉伸试验,发现纤维丝和纤维束的力学性能与试样的标距及结构尺度存在很大相关性,试样的拉伸强度会随着其标距的增加和结构尺度从纤维丝增大到纤维束而降低;随后,按照Weibull分布对试验数据进行统计分析,量化了不同标距下纤维丝和纤维束拉伸强度的随机变化程度;接着,考虑到纤维丝的拉伸强度符合Weibull分布随机破坏,利用ANSYS中的用户自定义子程序(USERMAT)建立了纤维丝本构模型;最后,采用纤维丝本构模型模拟纤维束的拉伸破坏行为,并讨论了关键参数对纤维束拉伸破坏行为的影响。结果表明:纤维束的模拟结果与试验结果吻合程度较好,所建模型可以较准确地预测纤维束的拉伸性能。      

不同应变率下Kevlar49纤维束拉伸力学性能的实验研究

利用M TS810材料试验机及旋转盘式杆杆型冲击拉伸试验装置对Kevlar49纤维束进行了准静态拉伸及冲击拉伸实验研究, 首次在应变率为10-4/ s～ 103/s 范围内得到了Kevlar49纤维束完整的应力应变曲线。实验结果表明, Kevlar49纤维束的力学性能是与应变率相关的。在低应变率下Kevlar49纤维束对应变率不太敏感, 但比玻璃纤维束高; 在高应变率下Kevlar49纤维束对应变率敏感, 但不如玻璃纤维束强烈; 中应变率区是Kevlar49纤维束由应变率不太敏感到应变率敏感的过渡区。      

Mg-3Al-2Zn-2Y合金的动态力学性能研究

在不同应变率压缩与拉伸下,研究了Mg-3Al-2Zn-2Y合金的力学性能,发现2种条件下合金力学性能变化规律不同。压缩情况下,随应变率增大,极限强度与屈服强度先增大后减小,高应变率下(1300～4800s-1)的流变应力大于中低应变率(0.001～1s-1);在0.001～1450s-1拉伸下,随应变率增大,合金的流变应力呈增大趋势,极限强度、屈服强度增大,破坏应变先减小后增大。压缩情况下合金流变应力的应变率敏感性高于拉伸情况。     

SiC 纤维的强度测试和评价

测定了 SiC(W 芯)纤维的抗张强度,实验表明:对用 CVD 法制备的 SiC(W 芯)纤维的抗张强度测试值随试样标距的增大而降低,其室温抗张强度呈正态分布状态。当纤维拉伸试样标距为50mm 和25mm 时,SiC(W 芯)纤维室温抗张强度分别为3584.2±403.7MPa 和3669.9±348.1MPa,其 Weibull 模数分别为9.8和11.9。     

再生混凝土动态直接拉伸的试验研究

利用大直径(75 mm)分离式霍普金森拉杆(SHTB),对再生粗骨料取代率分别为0%、25%、50%、75%和100%的5组圆柱体再生混凝土试样进行应变率范围为100~102s-1的动态直接拉伸实验,研究再生混凝土的动态直接拉伸力学性能及其破坏形态。试验结果表明,再生混凝土的抗拉强度随平均应变率的增加而增大,而再生混凝土的破坏形态与平均应变率有关,这表明再生混凝土具有明显的率敏感性。在相同水灰比下,再生混凝土准静态拉伸强度比普通混凝土低1.3%~15.9%,动态拉伸强度比普通混凝土低1.7%~29%,此研究为再生混凝土的工程应用提供一定的理论依据。     

Strain rate and gage length effects on tensile behavior of Kevlar 49 single yarn

In the present paper, Kevlar® 49 single yarns with different gage lengths were tested under both quasi-static loading at a strain rate of 4.2 × 10^?4 s^?1 using a MTS load frame and dynamic tensile loading over a strain rate range of 20–100 s^?1 using a servo-hydraulic high-rate testing system. The experimental results showed that the material mechanical properties are dependent on gage length and strain rate. Young’s modulus, tensile strength, maximum strain and toughness increase with increasing strain rate under dynamic loading; however the tensile strength decreases with increasing gage length under quasi-static loading. Weibull statistics were used to quantify the degree of variability in yarn strength at different gage lengths and strain rates. This data was then used to build an analytical model simulating the stress–strain response of single yarn under dynamic loading. The model predictions agree reasonably well with the experimental data.     

The effect of surface modification with carbon nanotubes upon the tensile strength and Weibull modulus of carbon fibers

Carbon fibers are widely used as reinforcements in composite materials because of their high specific strength and modulus. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6?GPa), and ultrahigh modulus pitch-based (more than 900?GPa) carbon fibers have been commercially available. In contrast, carbon nanotube (CNT) with the extremely high tensile strength have attracted attention as reinforcements. An interesting technique to modify the carbon fiber is CNT grafting on the carbon fiber surface. CNT-grafted carbon fibers offer the opportunity to add the potential benefits of nanoscale reinforcement to well-established fibrous composites to create micro-nano multiscale hybrid composites. In the present study, the tensile properties of CNT grown on T1000GB PAN- and K13D pitch-based carbon fibers have been investigated. Single filament tensile test at gauge lengths of 1, 5, and 25?mm were conducted. The effect of gauge length on tensile strength and Weibull modulus of CNT-grafted PAN- and pitch-based carbon fibers were evaluated. It was found that grafting of CNT improves the tensile strength and Weibull modulus of PAN- and pitch-based carbon fibers with longer gauge length (≥5?mm). The results also clearly show that for CNT-grafted and as-received PAN- and pitch-based carbon fibers, there is a linear relation between the Weibull modulus and the average tensile strength on log–log scale.     

Reduction in tensile and flexural strength of unidirectional glass fibre-epoxy with increasing specimen size

Size effects in tensile failure were investigated by means of tensile and four-point bending tests. Tapered tensile specimens with plies dropped off internally showed a reduction in strain at failure with increasing gauge length. Scaled bending tests also showed a reduction in strain with increasing specimen size. These two effects and the relationship between the tensile and flexural results could all be fitted satisfactorily with a Weibull strength model.     

The effect of gauge length on tensile strength and Weibull modulus of polyacrylonitrile (PAN)- and pitch-based carbon fibers

Carbon fibers are widely used as a reinforcement in composite materials because of their high specific strength and modulus. Current trends toward the development of carbon fibers have been driven in two directions; ultrahigh tensile strength fiber with a fairly high strain to failure (~2%), and ultrahigh modulus fiber with high thermal conductivity. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6 GPa), and ultrahigh modulus pitch-based (more than 900 GPa) carbon fibers have been commercially available. In this study, the tensile strengths of PAN- and pitch-based carbon fibers have been investigated using a single filament tensile test at various gauge lengths ranging from 1 to 250 mm. Carbon fibers used in this study were ultrahigh strength PAN-based (T1000GB, IM600), a high strength PAN-based (T300), a high modulus PAN-based (M60JB), an ultrahigh modulus pitch-based (K13D), and a high ductility pitch-based (XN-05) carbon fibers. The statistical distributions of the tensile strength were characterized. It was found that the Weibull modulus and the average tensile strength increased with decreasing gauge length, a linear relation between the Weibull modulus, the average tensile strength and the gauge length was established on log–log scale. The results also clearly show that for PAN- and pitch-based carbon fibers, there is a linear relation between the Weibull modulus and the average tensile strength on log–log scale.     

Statistical variability in the strength and failure strain of aramid and polyester yarns

The scatter in the failure strain, load and stress of high-tenacity polyester and aramid yarns is studied experimentally. From the data, the failure strains of polyester and aramid yarns can be fitted to a two-parameter Weibull distribution. However, the log-log dependence of the strain on the gauge length is best represented by the Watson-Smith modification. Whereas the strengths of polyester yarns are best described by the two-parameter Weibull distribution, those of aramid yarns are best represented by the Gumbel distribution. The effect of strain rate on the strength distribution of aramid yarns is also examined. The strength of aramid yarns decreases slightly with an increase in the strain rate. This is contrary to theoretical predictions but in line with other test data.     

23Co13Ni11Cr3Mo超高强钢的高温变形行为

在Glreeble 1500热模拟机上进行大变形等温压缩实验,研究了23Co13Ni11Cr3Mo钢的高温变形行为.结果表明:流变应力随着变形温度的降低和应变速率的升高而增大,在高温、低应变速率下动态再结晶软化效应显著,在温度为1000℃、应变速率为0.001 s-1时流变应力下降29.6％.23Co13Ni11Cr3...