长玻璃纤维/聚丙烯复合材料粒料注塑制品的拉伸强度

利用自行研制的玻璃纤维(GF)增强聚丙烯(PP)预浸装置,制备了长玻纤增强聚丙烯(LGFRP)粒料,并通过普通注塑机注塑成型。研究了界面改性、粒料长度、浸渍程度及退火处理等对注塑试样拉伸强度的影响。试验发现,用接枝马来酸酐PP作为界面相容剂,试样的拉伸强度明显提高。当接枝马来酸酐量占PP量的0.3 %左右时,试样强度达到最大值。长纤维粒料内纤维浸渍度越高,注塑试样的强度越好。15 mm和5 mm长纤维粒料注塑成型试样的拉伸强度均高于10 mm粒料注塑成型的试样。退火处理可较大程度地提高注塑试样的拉伸强度。     

不锈钢拉伸试验条件与断后伸长率测量值的关系

采用单向拉伸试验研究了不同拉伸速度、不同试样规格对不锈钢冷轧薄板断后伸长率测量值的影响。结果表明:不锈钢的断后伸长率测量值随拉伸速度的提高而下降、随试样横截面的增大而提高。说明拉伸试验条件对不锈钢薄板的断后伸长率测量值影响较大,只有在拉伸试验条件一致的情况下,断后伸长率测量值才能作为选材的依据之一。     

拉伸速度对金属材料拉伸性能测试结果的影响

本文通过测试LY12铝合金和45钢在不同拉伸速度下的抗拉强度和断后伸长率,对比分析拉伸速度对不同塑性的金属材料拉伸性能测试结果的影响。结果表明：拉伸速度的提高会造成抗拉强度的升高和断后伸长率的降低,同时拉伸速度对塑性大的材料的测试结果影响更大。     

医用级热塑性聚氨酯的拉伸性能测试

文中以医用级高分子聚氨酯(TPU)为原材料,通过热压成型制备厚1.2 mm TPU片材,并制取75×4哑铃型拉伸试样。在电子万能试验机上以较高的恒定拉伸速率进行拉伸,预先设定应力到某一设定值后停止拉伸,然后应力以一定速度进行减载。实验探索了整个拉伸-回复循环中应力与应变的关系,研究了拉伸速度对医用级TPU拉伸强度及断裂伸长率的影响,并对拉伸过程中出现应力发白现象进行探究。结果表明,TPU是一种强而韧的硬弹性高分子材料,在高应力大形变下由弹性提供的可逆形变约80%,粘性提供的不可逆形变约20%。在高应力下材料内部孔洞尺寸变大,由此引起材料由透明转而发白,此光学现象可反复发生。     

拉伸试验机自动测量断后伸长率面临的难题及解决办法

拉伸试验机、引伸计、试样测量台和机械手等技术的进步,使很多自动或半自动的拉伸试验机投入了使用,这些拉伸机测量抗拉强度、屈服强度等应力指标可以达到很高的精度,但是,自动测量断后伸长率却可能得出错误的结果。认识、验证和解决该问题是制造和使用拉伸机的有关人员面临的一个难题。介绍了笔者和某试验机制造公司共同进行的验证直接测量和不同修正方法得到的结果,并提出了用最大力总伸长率代替断后伸长率作为塑性指标。     

等规聚丙烯微注塑制品的形态结构和力学性能

选用等规聚丙烯材料,基于正交表L_(25)(5~6)进行微注塑成型实验,制备厚度为0.5 mm的微注塑拉伸试样。采用偏光显微镜和广角X射线衍射仪对其形态结构进行表征,并分析工艺参数对微制品形态结构的影响规律和影响度。对微制品试样进行拉伸实验,分析工艺参数对其屈服应力、弹性模量和断裂伸长率的影响规律和重要度。结果表明,注射速度对微试样的形态结构和力学性能的影响最大;皮层厚度和皮层取向度随着注射速度的增大而减小;屈服应力随注射速度、熔体温度的增大而减小;熔体温度对弹性模量和断裂伸长率的影响较大,且弹性模量随着熔体温度的升高而减小,断裂伸长率随着熔体温度的升高而增大。     

试样直径对TC4钛合金拉伸性能的影响

通过对不同直径的TC4钛合金试样进行室温拉伸试验,研究了试样直径对试验测得TC4钛合金抗拉强度、屈服强度、断后伸长率以及断面收缩率等拉伸性能的影响规律,并探讨了其影响机制。结果表明:试验测得TC4钛合金的抗拉强度和屈服强度随试样直径的增大呈指数函数关系下降,而断后伸长率和断面收缩率随试样直径的增大呈线性函数关系下降;该种变化规律是由不同直径试样TC4钛合金显微组织结构和加工方式等引起的。     

金属盘管的室温拉伸试验方法

分别采用试样两端压扁法、人工掰直法和矫直机矫直法对H68黄铜盘管和BFe10-1-1白铜盘管进行室温拉伸试验，并对试验结果进行分析。结果表明：对于壁厚不小于1 mm、断后伸长率不小于60%的金属盘管，试样端部压扁后，可以有效地进行室温拉伸试验；对于壁厚小于1 mm、断后伸长率小于40%的金属盘管，采用正压法可以提高试验成功率；当试样允许矫直，或屈服强度无要求时，将试样进行整体矫直更容易操作。     

热拉伸比对PET/ PE 原位微纤化复合材料形态和拉伸性能的影响

采用熔融挤出2热拉伸2淬冷方法制备了聚对苯二甲酸乙二醇酯( PET) / 聚乙烯( PE) 原位微纤化复合材料。固定体系组成( PET/ PE 为15/ 85), 热拉伸比增加, PET 粒子相继从球状转变成椭球状、棒状和纤维状; 除了最小粒径保持基本不变外, 最大和平均粒径均逐渐减小。微纤化复合材料在PE 的加工温度下成型时, 纤维能够良好地保持在体系中, 但在PET 的加工温度下成型时, 纤维重新熔融, 形成球状粒子。复合材料的拉伸模量和拉伸强度随拉伸比增加显著增加, 表明微纤化对材料具有良好的增强效果; 而断裂伸长率随热拉伸比增加剧烈下降, 产生明显的韧-脆转变。比基本断裂功( we ) 先随热拉伸比( HSR) 增加而增加, 热拉伸比为19117 左右时达到最大值, 继续增加热拉伸比, we 降低。      

拉伸试样断头原因分析

金属材料在拉伸测试过程中常会发生拉伸试样断头现象,影响拉伸试样伸长率的准确测定。就拉伸试样断头现象进行分析,找出了拉伸试样潜在的材料、形状、尺寸及标记等影响因素,针对这些因素在拉伸试样尺寸、制样及检验环节制定针对性的措施,在一定程度上可对拉伸试样的断头进行有效控制,为降低甚至避免拉伸试样的断头提供必要的参考。     

SiC填充PP/FA复合材料拉伸强度及分形特征

目的定量研究不同含量碳化硅晶须(SiC)对聚丙烯(PP)/粉煤灰(FA)复合材料拉伸强度以及拉伸断口复杂程度的影响。方法以聚丙烯为基体,马来酸酐接枝聚丙烯(PP-g-MAH)为相容剂,FA和SiC为填料,采用熔融共混法制备PP/FA/SiC复合材料。利用电子万能试验机测试复合材料的拉伸强度,同时采用扫描电镜对拉伸断口进行形貌分析,并基于分形原理,利用差分盒维计数法计算复合材料拉伸断面的分形维数,分析研究复合材料拉伸断面的分形维数与其拉伸强度间的关系。结果复合材料的拉伸断面分形维数在1.24~1.90之间,相关系数均大于0.9,说明其具有统计意义上的自相似和较强的相关性。结论复合材料拉伸强度的对数与其断面的分形维数呈线性函数关系。     

湿热老化对APMOC纤维拉伸性能的影响

通过湿热老化试验,研究了APMOC纤维吸湿性能、拉伸强度、断裂延长率以及弹性模量随老化时间的变化。结果表明:经湿热老化后,APMOC纤维的吸湿特性符合Fick第二定律,拉伸强度、断裂延伸率呈明显下降趋势。利用扫描电镜(SEM)对拉伸断口进行了分析,发现湿热老化前期,湿热对APMOC纤维主要是增塑作用,后期主要是脆化作用。对不同湿热条件进行比较,80℃、相对湿度85%时,APMOC纤维性能变化更为显著。     

低填充SiO_2/聚丙烯纳米复合材料的拉伸特性

通过对纳米 Si O2 辐照接枝聚合改性 ,结合熔融共混工艺制备了低填充 Si O2 / PP纳米复合材料。发现在一定拉伸速度和粒子含量下 ,经辐照改性的 Si O2 / PP纳米复合材料韧性得到显著提高 ,同时强度也有所增加。随拉伸速度的升高 ,纳米复合材料的模量和强度逐渐增大 ,而韧性则随之下降。断面扫描电镜观察表明 ,改性纳米粒子填充复合材料韧性提高的机理以空化和基体大面积剪切屈服为主     

E460钢拉伸性能与试验温度相关性研究

通过金相显微镜、扫描电镜、透射电镜等手段对E460钢的微观组织、低温条件下试验温度对E460钢拉伸性能的影响进行了研究。试验结果表明,在设计的试验温度范围内,随着试验温度的降低,E460钢的强度与伸长率均有所增加,表现出明显的增强增韧现象。     

Tensile Properties of Electrodeposited Nanocrystalline FCC Metals

Bulk nanocrystalline Ni and Ni-15wt%Fe alloy were fabricated via electrodeposition techniques. The nominal grain size of nickel samples was varied from 15 to 200 nm by employing different deposition parameters. The grain size was further reduced to 9 nm by alloying nickel with iron. The tensile properties were evaluated at room temperature using dog-bone shaped samples. The results of this study confirm that strength and strain hardening rate increase with decreasing grain size. The fracture behavior was found to depend on the grain size, presence of large and small defects, and the stress state. The tensile elongation and reduction in area varied significantly among the samples and did not correlate with the fracture behavior. Three categories of behavior were identified. In Type I the samples showed completely ductile fracture but very low tensile elongation. In Type II the samples showed a relatively brittle behavior but impressive tensile elongation. In Type III the samples showed ductile behavior with reasonable tensile elongation. In this article, the tensile elongation and the fracture mode of nanocrystalline face centered cubic (FCC) metals are discussed in terms of deformation behavior and presence of defects.     

Impact Tensile Stress–strain Characteristics of Wrought Magnesium Alloys

Abstract:  Impact tensile properties of three different wrought magnesium alloys (AZ31B-F, AZ61A-F and ZK60A-T5) are evaluated using the split Hopkinson bar. Reliable tensile stress–strain data up to fracture in the extrusion direction at strain rates of nearly 1000 s⁻¹ are presented and compared with those at quasi-static and medium rates of strain obtained on an Instron testing machine. The effect of strain rate on the tensile strength, elongation at fracture and absorbed energy is examined in detail. It is demonstrated that the tensile strength increases with increasing strain rate, and the strain-rate dependence of elongation at fracture and absorbed energy varies, depending on the magnesium alloys tested. The limitations of the test technique are discussed.     

Tensile and compressive properties of chopped carbon fiber tapes reinforced thermoplastics with different fiber lengths and molding pressures

Tensile and compressive behaviors of chopped carbon fiber tapes reinforced thermoplastics have been investigated by varying compression molding conditions (to study the effect of the molding pressure) and the tape length (to analyze the fiber length effect on the mechanical properties of produced composites). Fractographic analysis of prepared specimens conducted after the experiments indicated that the obtained modulus values were almost independent of both the tape length and molding pressure, while the measured strengths exhibited high molding pressure sensitivity. Interlaminar shear strength was considered to be the dominate factor in damage determination during tensile testing, while interlaminar tensile strength played the main role in compression fracture. Increase in the tape length led to a slight increase in the strength magnitude, but also a significant increase in the standard deviation of strength due to the decrease in structural regularity.     

1Cr18Ni9Ti钢的低温拉伸变形行为

对1Cr18Ni9Ti钢在室温和低温下进行拉伸试验,利用TEM分析拉伸试样断口附近的显微组织,用SEM对拉伸断口进行观察,研究了温度对1Cr18Ni9Ti钢拉伸变形行为的影响.研究表明:随着试验温度的降低,1Cr18Ni9Ti钢的抗拉强度与屈服强度及加工硬化指数单调增加;延伸率呈降低趋势,并在温度降至77 K时略有回升;拉伸断口附近显微组织中出现板条马氏体,且温度降低,板条马氏体数量增加;低温与应变共同作用诱发板条马氏体形成是影响1Cr18Ni9Ti钢低温拉伸变形行为的重要因素.     

Influence of Shock Pre‐Compression Stress and Tensile Strain Rate on the Spall Behaviour of Mild Steel

Abstract: A series of plate‐impact spall experiments were conducted to investigate the influence of shock pre‐compression stress and tensile strain rates on the dynamic tensile fracture (or spall) behaviour of shocked mild steel. The shock pre‐compression stress amplitude and tensile strain rate were controlled independently to ensure that only one single‐loading parameter varied for each experiment. A push–pull type velocity interferometer system for any reflector (VISAR) was used to measure the free surface velocity profiles of samples. It is observed from experimental results that the influence of shock pre‐compression stress amplitude on the spall strength is less significant in the range attained in these experiments, whereas with increasing tensile strain rate, an evident 65% increase of spall strength is determined in the present tensile strain rate range of 10⁴ to 10⁶ s^?1. VISAR data are compared with finite‐difference calculations employing a modified damage function model with a percolation–relaxation function, and a good agreement between the calculation and the experiments was obtained. Preliminary simulation results also revealed that a critical damage exists, which physically corresponds to the critical intervoid ligament distance for triggering the onset of void coalescence, and may be regarded as a material parameter for describing the dynamic tensile fracture and independent of the loading conditions.