基于CT技术的黄原胶加固土干湿循环条件下力学性能和微观结构劣化机制研究

干湿循环对岩土体的工程特性具有重要影响。采用CT扫描技术和力学测试,对加入不同含量黄原胶(0%,0.5%,1.5%)加固的黏土在经历不同次数(0,1,4,8,12次)干湿循环作用下的力学性能和微观结构劣化机制进行了研究,得到结论:(1)黄原胶能够有效提高土体的抗压强度和耐干湿循环效果。随着黄原胶含量的增加,干湿循环作用后的强度损失逐渐减小,当循环次数从0次增加到4次时,对于加入黄原胶含量分别为0%,0.5%,1.5%的试样,抗压强度分别损失了42.75%,17.2%,14.04%。(2)加固土的抗压强度与干湿循环次数之间保持指数下降的关系,当循环次数达到4次后,随着循环次数的进一步增加,抗压强度和弹性模量均在较小的变化范围内波动。(3)随着干湿循环次数的增加,黄原胶加固土的孔隙率表现出先增加后减小的趋势,连通孔隙不断扩展,而孤立孔隙表现出先增加后减小的趋势。(4)随着试样的干燥,黄原胶在土颗粒间形成网状基质,提高土体的强度和耐干湿循环能力。

基于岩石CT扫描的冻融作用对花岗岩细观结构及力学强度影响研究

近年来随着西部地区的基础工程建设数量及规模不断增加,西部高原地区的季节性冻融循环效应的影响也随之增强,开展冻融循环作用下岩石细观特性及强度劣化性质研究对指导西部寒区基础工程建设至关重要。首先在偏光显微镜下对岩石薄片进行观察,获取岩石的矿物成分和微结构;接着利用CT扫描技术,对冻融后的花岗岩进行扫描,对扫描图层利用阈值分割进行二值化处理,堆叠得到样品内外结构的高分辨3D数据及影像;结合分形理论计算图像计盒维数并由此对图像复杂度做出量化判断,由此对冻融循环对花岗岩内部结构演化分布特点进行分析;进而揭示其强度演化规律,探究结构演化与强度之间的关系。偏光显微镜下,岩石呈块状构造,具有似斑状粗粒不等粒花岗结构,局部见交代蠕虫结构。似斑晶矿物主要为碱性长石;其他矿物粒径0.25~4.0 mm为主,矿物成分主要为石英、斜长石、碱性长石,次要矿物为黑云母、绿帘石,副矿物有磷灰石、锆石、黄铁矿等,镜下鉴定为似斑状粗粒不等粒黑云二长花岗岩。CT扫描显示,冻融循环效应在影响花岗岩细观结构时,会导致花岗岩内部孔隙率的整体上升,但岩石渗透性变化不大,岩石渗透率仅上升0.003×10^(-3)μm^(2);内部孔隙发育不均匀,试样整体结构改变以萌生较多新的微孔隙为主。冻融循环后岩石内部结构复杂度有所下降,但岩石整体完整性仍然较好,分形维数仍保持在较高水平。分形研究显示,20次冻融循环并未导致花岗岩的结构复杂度发生较大变化,同时试样整体力学特性出现下降,黏性增加以及长期强度出现较大幅度的衰减,进入蠕变试验阶段的应变阈值提高。在评价此类原生结构较致密的岩石的安全性时,仅从结构上进行考量与实际情况往往会出现偏差,应结合必要的强度指标综合评估。岩石在经历冻融循环后,在强度更低的同时会发生更大的变形。该研究可为分形理论在岩石细观结构演化方面的应用及岩石细观结构与强度演化相关研究提供借鉴,并对高寒地区工程施工有指导意义。

Ultra-high cycle fatigue behavior of high strength steel with carbide-free bainite/martensite complex microstructure

The ultra-high cycle fatigue behavior of a novel high strength steel with carbide-free bainite/martensite （CFB/M） complex microstructure was studied. The ultra-high cycle fatigue properties were measured by ultrasonic fatigue testing equipment at a frequency of 20 kHz. It is found that there is no horizontal part in the S-N curve and fatigue fracture occurs when the life of specimens exceeds 10^7 cycles. In addition, the origination of fatigue cracks tends to transfer from the surface to interior of specimens as the fatigue cycle exceeds 10^7, and the fatigue crack originations of many specimens are not induced by inclusions, but by some kind of ＂soft structure＂. It is shown that the studied high strength steel performs good ultra-high cycle fatigue properties. The ultra-high fatigue mechanism was discussed and it is suggested that specific CFB/M complex microstructure of the studied steel contributes to its superior properties.

Microstructure and Mechanical Properties of Aer Met 100 Ultra-high Strength Steel Joints by Laser Welding

AerMet100 ultra-high strength steel plates with a thickness of 2 mm were welded using a COz laser welding system. The influences of the welding process parameters on the morphology and microstructure of the welding joints were investigated, and the mechanical property of the welding joints was analyzed. The experimental results showed that the fusion zone of welding joint mainly consisted of columnar grains and a fine dendrite substructure grew epitaxially from the matrix. With the other conditions remaining unchanged, a finer weld microstructure was along with the scanning speed increase. The solidification microstructure gradually transformed from cellular crystal into dendrite crystal and the spaces of dendrite secondary arms rose from the fusion line to the center of the fusion zone. In the fusion zone of the weld, the rapid cooling caused the formation of martensite, which led the microhardness of the fusion zone higher than that of the matrix and the heat affected zone. The tensile strength of the welding joints was tested as 1 700 MPa, which was about 87% of the matrix. However, the tensile strength of the welding joints without defects existed was tested as 1832 MPa, which was about 94% of the matrix.

Comprehensive evaluation of chemical breakers for multistage network ultra-high strength gel

Polymer gels have been accepted as a useful tool to address many sealing operations such as drilling and completion,well stimulation,wellbore integrity,water and gas shutoff,etc.Previously,we developed an ultra-high strength gel(USGel)for medium to ultra-low temperature reservoirs.However,the removal of USGel is a difficult problem for most temporary plugging operations.This paper first provides new insights into the mechanism of USGel,where multistage network structure and physical entanglement are the main reasons for USGel possessing ultra-high strength.Then the effects of acid breakers,encapsulated breakers,and oxidation breakers(including H_(2)O_(2),Na_(2)S_(2)O_(8),Ca(ClO)_(2),H_(2)O_(2)+NaOH,Na_(2)S_(2)O_(8)+NaOH,and Ca(ClO)_(2)+NaOH)were evaluated.The effects of component concentration and temperature on the breaking solution were studied,and the corrosion performance,physical simulation and formation damage tests of the breaking solution were carried out.The final formulation of 2%-4%NaOH+4.5%-6%H_(2)O_(2) breaking solution was determined,which can make USGel completely turn into water at 35e105C.The combinations of“acid t breaking solution”,“acid+encapsulated breaker”and“encapsulated breaker+breaking solution”were evaluated for breaking effect.The acid gradually reduced the volume of USGel,which increased the contact area between breaking solution and USGel,and the effect of“4%acid+breaking solution”was 23 times higher than that of breaking solution alone at 35C.However,the acid significantly reduced the strength of USGel.This paper provides new insights into the breaking of high-strength gels with complex network structures.

Analysis of the effect of geometrical parameters on fatigue performance of spot-weld joint for ultra-high strength steel

This paper studied the spot welding structure of ultra-high strength steel 22MnB5.ANSYS software was adopted to simulate its static strength;BS5400 algorithm was used to calculate the fatigue life;and the grouping method was used to test the fatigue performance of tensile shear spot weld specimens.The simulation results were in good agreement with the experimental values.Based on the validation of the simulation method,influences of different structural parameters on static strength and fatigue life were explored by adopting single factor.The results showed that within the selected structure parameter range,increase of the sheet thickness,nugget diameter,sheet width and overlapping length can lead to longer fatigue life.Besides,the fatigue life of spot weld took on a linear relationship with the overlapping length,a DoseResp relationship with the sheet thickness,and a single exponential decay relationship with the sheet width and the nugget diameter.Moreover,in order to estimate the impact from various parameters on the fatigue life of the specimens,the Taguchi orthogonal design method was applied in the simulation design.The simulating result indicated that influence of the sheet thickness on fatigue life was the most significant.In addition,the effects of nugget diameter,sheet width and overlapping length on fatigue life were reduced in turn.

The temperature-dependent fracture strength model for ultra-high temperature ceramics

Breaking down the entire structure of a material implies severing all the bonds between its atoms either by applying work or by heat transfer. Because bond-breaking is indifferent to either means, there is a kind of equivalence between heat energy and strain energy. Based on this equivalence, we assume the existence of a constant maximum storage of energy that includes both the strain energy and the corresponding equivalent heat energy. A temperaturedependent fracture strength model is then developed for ultrahigh temperature ceramics （UHTCs）. Model predictions for UHTCs, HfB2, TiC and ZrB2, are presented and compared with the experimental results. These predictions are found to be largely consistent with experimental results.

基于CT图像三维重建的高温下再生混凝土孔隙特征研究

高温会导致混凝土微细观结构损伤劣化,进而导致混凝土力学性能下降。本工作利用计算机层析成像(CT)技术对高温后掺加玻化微珠的再生混凝土(Recycled aggregate concrete mixed with glazed hollow beads, GHB-RAC)试件孔隙结构特征进行识别,基于CT扫描与三维重构建模提取并分析了混凝土孔隙结构的特征参数,同时利用灰色关联理论探究孔隙结构特征参数对混凝土残余抗压强度的影响程度。研究结果表明,温度会影响GHB-RAC内部孔隙结构,内部孔隙孔径及表面积随温度升高而增大,温度的升高也会影响混凝土孔隙均匀性,加剧孔隙不均匀性分布;玻化微珠(Glazed hollow beads, GHB)对混凝土温度传导的阻碍作用明显,GHB的掺入改善了混凝土的孔隙结构,减弱了高温导致的孔隙畸化;孔隙尺寸、孔隙球体度及孔隙表面积与残余抗压强度的灰色关联度均在0.55以上,表明孔隙结构参数与残余抗压强度关联性较好。

Internal oxidation of hot-rolled ultra-high strength steel and its effect on the surface quality of cold-rolled sheets

In this study,the scale and internal oxidation of hot-rolled ultra-high strength steel sheets were characterized.It was found that both the formation of the scale and the internal oxidation of Si and Mn depended on the coiling temperature and position of the steel sample on the strip coil.At a relatively high coiling temperature,a large amount of internal oxidation was observed on the samples cut from the middle of the coil.The depth of the internal oxidation zone exceeded 10 μm and a thin iron layer covering the scale was observed in some cases.Pickling and cold-rolling experiments were conducted on selected samples.Scale pickling was found to be greatly delayed by the formation of an iron layer,which frequently resulted in under-pickled defects.In addition,pickling of the entire internal oxidation zone was difficult,except at the grain boundaries,where the degree of internal Si and Mn oxidation was enriched.The surface of the cold-rolled steel sheet was ruined by the remaining oxidation zone in the subsurface of the pickled steel.The internal oxidation of hot-rolled ultra-high strength steel must be precisely controlled to improve the subsequent surface quality of cold-rolled steel.

基于CT扫描植物根-土复合体直剪试验研究

为探究植物根系对土壤的作用机理,以构树、刺槐、枸杞根为研究对象,通过重塑根-土复合体直剪试验、CT扫描试验,分析了三种植物根系的固土机理。试验结果表明:三种植物根系的存在能够有效地提升土样的抗剪强度与变形能力,其中构树根的增强效果最为显著;较未含根试样含构树根试样内摩擦角提升70.3%,含刺槐根试样黏聚力提升74.8%;根系对土样剪切裂缝的扩展有显著的抑制作用,裂缝的宽度与长度均比未含根试样的小,三种植物中构树根系对土体的加固作用较优。该研究结果为植物根系的固土护坡机理提供理论支撑。

基于CT技术的喷射混凝土粗骨料与孔隙分布规律研究

混凝土粗骨料和孔隙是影响其力学强度的重要因素,本研究基于CT扫描技术,对浇筑和喷射两种工艺制作的混凝土试件的粗骨料、孔隙分布和力学强度进行研究,分析混凝土粗骨料和孔隙分布规律。结果表明:浇筑和喷射混凝土骨料存在分层现象,但呈现规律不同,浇筑混凝土粗骨料呈两层分布,分层临界点大约在试件50 mm处,靠近试件底部粗骨料体积增加16%;喷射混凝土粗骨料呈三层分布,临界点位于试件30、70 mm处,在近壁面30 mm区域粗骨料回弹严重,体积减少50.45%,试件中部30~70 mm区域,粗骨料分布均匀且密集,但仍少于浇筑混凝土,喷射试件末端70~98 mm区域骨料数量和体积有所下降,但高于近壁面区域;孔隙分布受骨料分布影响,大孔隙主要沿骨料边缘分布,总体上喷射混凝土孔隙率高于浇筑混凝土且形状不规则,0.1~0.4 mm孔径孔隙数量较多。结合骨料分布和孔隙率的特点,分析了粗骨料分布、孔隙率对混凝土抗压强度的影响。

基于CT扫描岩石蠕变扰动特性单轴压缩试验研究

工程深部开采活动中,岩石周围应力环境较为复杂,且对扰动作用极为敏感。在已经提出的岩石“蠕变扰动效应”以及“强度极限邻域”概念的前提下,利用CT技术手段对岩石“强度极限邻域”内、外进行微观扫描探测,观察岩石内部损伤变化过程,同时运用单位像素坐标点建立孔隙之间距离,并结合工程实例得出以下结论:①分析横、纵应力-应变曲线可知,岩石在纵向与横向同时存在一个长期强度,且岩石进入横向长期强度优先纵向,但是通过CT扫描岩石内部孔隙结构变化可知,岩石纵向长期强度阈值相比横向更准确;②通过分析岩石轴向CT扫描图,在轴压45MPa时,岩石内部只出现新的较少孔隙结构,且内部孔隙并未出现相连贯通现象;而在轴压50MPa时,未扰动时就可清楚看出岩石内部新的孔隙结构出现贯通现象,随着扰动的施加,岩石内部出现明显的裂痕条纹,说明岩石“强度极限邻域”为45~50MPa,可知以纵向长期强度判断“强度极限邻域”更具有说服力;③对CT扫描后的岩石试件进行伪彩色处理,利用岩石像素特征点之间的距离建立孔隙之间的距离,通过分析轴压40MPa与45MPa下岩石扰动前后的像素特征点之间距离可知,其只是略微的增加或减少;而在轴压50MPa下,岩石扰动前后像素特征点坐标值出现突增,像素特征点间的距离增加了214.27,说明岩石“强度极限邻域”为45~50MPa,且岩石在此轴压时对扰动极为敏感;④结合工程实例分析,判断其岩石“强度极限邻域”,通过应变曲线变化范围为工程实例及时提供有效预警,同时也为地下工程的岩石扰动提供理论依据。

高速率生理盐水联合高强度深度学习重建算法对“三低”头颈部CTA图像质量的影响

目的 探讨高速率生理盐水联合高强度深度学习重建(High-Strength Deep Learning Image Reconstruction,DLIR-H)算法对“三低”(低管电压、低对比剂用量、低对比剂注射速率)头颈部CT血管造影(CT Angiography,CTA)图像质量的影响。方法 前瞻性收集于我院行头颈部CTA检查的90例患者,随机分为A、B、C组,每组各30例。A组以4.5 mL/s的速率注射50 mL对比剂,以3.0 mL/s的速率注射40 mL生理盐水,采用120 kVp,使用60%自适应迭代重建(Adaptive Statistical IterativeReconstruction-V,ASIR-V)算法重建;B组以3.0mL/s的速率注射30mL对比剂,以3.0mL/s的速率注射40mL生理盐水,采用80 kVp,使用60%ASIR-V算法重建;C组以3.0 mL/s的速率注射30 mL对比剂,以5.0 mL/s的速率注射40 mL生理盐水,采用80 kVp,使用DLIR-H算法重建。比较3组图像间的CT值、图像噪声(Standard Deviation,SD)、信噪比(Signal to Noise Ratio,SNR)、对比噪声比(Contrast to Noise Ratio,CNR)、CT容积剂量指数(CT Dose Index Volume,CTDIvol)及CT剂量长度乘积,比较3组图像质量的主观评分。结果 3组图像的CT值、SD值、SNR及CNR的差异均具有统计学意义(P<0.001)。C组在上腔静脉处CT值低于A、B组,其余各目标血管CT值、SNR及CNR均高于A、B组。C组各目标血管SD值小于B组,差异具有统计学意义(P<0.05);C组与A组的SD值差异无统计学意义(P>0.05)。C组CTDIvol、有效辐射剂量、对比剂用量较A组分别降低了55%、54%、40%。3组图像的主观评分差异具有统计学意义(P<0.001),C组与A组的差异无统计学意义(P>0.05)。结论 在“三低”技术下高速率生理盐水联合DLIR-H算法在头颈部CTA中的应用不仅能获得与常规剂量相当的图像质量,还可以使辐射剂量、对比剂用量和对比剂注射速率均明显减少。

CT扫描视域下黏土干湿循环劣化机理

为研究干湿循环对黏土力学特性和微观结构的影响,通过一系列无侧限抗压强度试验和CT扫描测试从宏观和微观角度揭示了干湿循环对黏土的劣化机理。结果表明:随着干湿循环次数的增加,黏土的抗压强度保持指数性下降趋势,在经历4次循环后,抗压强度损失了40%左右,干湿循环达到8次后抗压强度基本达到稳定;CT扫描横剖面显示,在干湿循环过程中,裂隙从试样四周开始发育,并逐渐向内部扩展,裂隙的宽度和长度均持续增加,连续性也有所提高;随着干湿循环次数的增加,试样的逐层面孔隙率均明显增加,且不同层间的交界面孔隙率的增加更为显著,层间的裂隙最先发育,试样表面也有竖向裂隙发育,试样内部连通孔隙的数量增加,闭合孔隙的数量减小;不同次数干湿循环作用下黏土的孔隙率与抗压强度之间保持负指数性关系,当干湿循环次数达到4次后,孔隙率的增加对抗压强度的影响减小。

64排MSCT、高场强MRI血管成像应用于急性主动脉综合征患者中的临床价值对比

目的 对比64排MSCT、高场强MRI血管成像应用于急性主动脉综合征患者中的临床价值。方法 回顾性分析本院2017年3月至2019年7月收治的90例急性主动脉综合征患者的临床资料,观察MRI检查及MSCT检查的诊断结果进行讨论和分析;对比经MRI检查、MSCT检查对急性主动脉综合征的诊断准确性、敏感性和特异性及两种检查相关指标。结果 经MRI检查对急性主动脉综合征的诊断灵敏性、特异性和准确性分别为92.22%、81.11%、97.78%,MSCT检查对急性主动脉综合征的诊断灵敏性、特异性和准确性分别为88.87%、76.67%、95.56%,MRI检查对急性主动脉综合征的诊断灵敏性、特异性和准确性高于MSCT检查,但两者比较差异无统计学意义(P>0.05);MRI血管成像的图像质量评分高于MSCT血管成像,信噪比低于MSCT血管成像,差异具有统计学意义(P<0.05)。结论 MSCT、高场强MRI血管成像均可有效显示急性主动脉综合征的影像学特点,均可作为辅助诊断急性主动脉综合征的有效手段,临床可结合患者自身情况进行选择。

Manifestations in Corrosion Prophase of Ultra-high Strength Steel 30CrMnSiNi2 A in Sodium Chloride Solutions

The corrosion behaviors of ultra-high strength steel 30CrMnSiNi2A in sodium chloride solution were studied by weight loss and electrochemical methods. The morphology of corrosion products was observed using scanning electron microscopy（SEM） and the composition was analyzed using an energy dispersive spectroscopy（EDS） and X-Ray diffraction （XRD）. The experimental results showed that the corrosion came from pitting corrosion and the rust layer was composed of outer rust layer γ-FeOOH and inner rust layer Fe_2O_3 with a little β-FeOOH. The correlation between corrosion rate and test time accorded with exponential rule. The corrosion current measured by polarization methods was higher than that calculated by weight loss method after a long-time immersion, the main reason was that,β-FeOOH and γ-Fe_2O_3 transformed by γ-FeOOH led to overestimating corrosion rate. The processes of corrosion prophase were obtained from XRD and EIS results. The corrosion product, Fe（OH）_2 formed at the initial stage stayed at a non-steady state and then consequently transferred to γ-FeOOH, γ-Fe_2O_3 or β-FeOOH.

Research and development of hot-rolled ultra-high strength steel at Baosteel

The effects of the composition and cooling process on the microstructures and properties of hot-rolled ultra-high strength low alloy （HSLA） steel, complex phase steel and martensite steel were studied in the laboratory. And S700MC and MP1200 ultra-high strength steels were trial produced at the 1 880 mm hot-rolling line of Baosteel. Compared with conventional hot-rolled high strength products,the idea that water is alloy was applied in the newly developed hot-rolled ultra-high strength steel. By the use of the economical composition design and controlled cooling after hot-rolling effectively,ultra-high strength steel of different steel grades can be obtained.

Corrosion Behavior of Ultra-high Strength Steel 300M in Different Simulated Marine Environments

Corrosion behavior of 300M in neutralcorrosion environments containing Na Clsimulated by totalimmersion（TI）,salt spraying（SS）and periodic immersion（PI）,was investigated by surface analysis techniques,corrosion weight-loss method,and electrochemicalmeasurements.In totalimmersion environment,rust on the steelconsisted of a porous outer rust layer with main constituent of γ-Fe OOH,and an inner rust layer of dense Fe_3O_4 film with network broad cracks.In salt spraying environment,outer rust with main composition of γ-Fe OOH/α-Fe OOH/Fe_3O_4 was compact,and inner rust showed dense Fe_3O_4 film.Rust formed by periodic immersion exhibited a compact outer rust layer with constituent of α-Fe OOH/γ-Fe OOH/Fe_3O_4 and an inner rust layer with composition of α-Fe OOH/α-Fe_2O_3;inner rust showed a ultra-dense film adherent to the steel.The corrosion rate showed a rule of vss（salt spraying）〉vti（totalimmersion）〉〉vpi（periodic immersion）in 0-240 h,and vss≈vti？vpiin 240-720 h.The rust formed by periodic immersion was dense and compact,with stable electrochemicalproperties,and had excellent protection on the steel.Humidity and oxygen concentration in allthe environments played major roles in rust formation.

Comparison of the Pull-out Strength Between a Novel Micro-dynamic Pedicle Screw and a Traditional Pedicle Screw by Using Pull Out Test and Micro-CT

Objective To investigate the effectiveness of the micro-dynamic pedicle screw for the prevention of loosening between the screw and bone surface in lumbar spinal fusion.For this evaluation,the peek pull-out force(PPF)after fatigue resistance testing at different cycles and semidiameter of screw insertion area of micro-CT image was compared between the micro-dynamic and traditional pedicle screws.Methods Forty lumbar vertebrae received a traditional pedicle screw on one side and a micro-dynamic pedicle screw on the other side as follows:15 vertebrae underwent instant pull-out testing(group A,traditional vs.group B,micro-dynamic);15 vertebrae underwent pull-out test after 5000-cyclic fatigue loading(group C,traditional vs.group D,micro-dynamic);and 10 vertebrae underwent pull-out test after 10000-cyclic fatigue loading(group E,traditional vs.group F,micro-dynamic).All vertebrae that after fatigue loading were scanned by using micro-ct to check the semidiameter of screw insertion area.The PPF,normalized PPF(PPFn),bone mineral density(BMD)and diameter of screw insertion area were compared between all groups.Results The BMD showed a weak significant correlation with PPF(r=0.252,P=0.024).The PPF in groups A and B(P=0.485),and groups C and D(P=0.184)did not show significant difference.However,the PPF in group F was significantly greater than that measured in group E(P=0.005).The PPFn of groups A,C,and E significantly decreased as the number of cycles increased(P=0.015).Meanwhile,the PPFn of groups B,D,and F remained consistent regardless of the number of cycles(P=0.367). The semidiameter of traditional pedicle screw insertion area was significantly larger than that of micro-dynamic pedicle screw insertion area(P<0.001).Conclusions This study compared the performance of a micro-dynamic pedicle screw versus that of a traditional pedicle screw using pull-out testing and micro-CT.The results showed that the micro-dynamic pedicle screw provides similar resistance in lowcycle fatigue testing and favorable resistance in high-cycle fatigue testing versus the traditional pedicle screw.The micro-dynamic pedicle screw provides stronger fixation stability versus the traditional pedicle screw,especially in high-cyclic fatigue loading condition versus the traditional pedicle screws.

PREPARATION AND CHARACTERIZATION OF ULTRA-HIGH MOLECULAR WEIGHT POLY(ETHYLENE TEREPHTHALATE)(PET)FIBER

This paper reports the spinning and drawing behavior of Ultra-high Molecular Weight polyethylene Terephthalate) (UHMW-PET) fibers. The as-spun fibers were produced by dry-jet wet spinning of a 15%-17% solution in 50:50(v:v) trifluroroacetic acid and dichloromethane. Both molecular weight and polymer solution concentration have marked effect on the drawability of the as-spun-fibers. The maximum extension drawing ratio (EDRmax) of as-spun fiber increases with increasing molecular weight, whereas optimal concentration to achieve the EDRmax of as-spun fibers decreases with increasing molecular weight. Drawing speed and temperature during the first step have remarkable effect on the drawability of these fiber during the second step. Relatively lower drawing temperature and drawing speed (19 ℃ , 60 mm/min) during the first drawing step was beneficial to mechanical properties of ultimate fibers. At the range of 210 ℃ to 230 ℃, the draw ratio (DR) during the second step increases with increasing temperature.