平纹编织CFRP制孔分层形成机制的热-力学理论建模及试验分析

碳纤维增强复合材料(Carbon fiber reinforced plastics,CFRP)在航空航天领域获得了广泛应用，但由于各向异性和层间连接较差等特点，钻削过程中极易出现分层缺陷，严重影响构件的使用性能。为分析钻削温度对平纹编织CFRP制孔缺陷的影响机制，基于弹性地基梁理论、黏聚力学模型和热力学理论，建立了新钻型钻削平纹编织CFRP制孔分层形成的理论模型。结果表明：当新钻型多刃尖(Ⅲ)钻削孔边缘的最表层材料时，钻削温度达到最大值，对最终分层的形成最为关键；钻削温度和制孔分层随着主轴转速的增大而逐渐降低，随着进给速度的增大而逐渐升高。当纤维角度(θ)在0°/90°/180°/270°附近时，层间分层的临界轴向力达到最大值，分层相对较大，当纤维角度(θ)在45°/135°/225°/315°附近时，临界轴向力最小，分层并非极大。因此，临界力的大小只能反映产生分层缺陷的难易程度，不能决定分层的最终形状和大小。考虑温度影响时的制孔分层形态预测与试验观测基本吻合，而不考虑温度影响下所获得的预测值总体上偏小。此外，平纹编织CFRP分层形状基本呈近似圆形。     

新型圆板牙螺纹刀具的设计

1　引言圆板牙是加工小尺寸的外螺纹刀具,其结构如图1所示。为了容纳切屑及形成刀刃,在板牙中钻出3～7个排屑孔,并在螺纹两端配置有切削锥部,板牙的切削锥部担负主要切削工作,中间的完整螺纹部分起校准和导向作用。切削锥部的锥角一般取2kr=40°～50°,l1=(15～25)P,l2=(4～5)P(P为螺距)。切削锥部的前角取15°～20°,后角通过铲磨获得,一般取5°～9°。外圆上的60°缺口槽是在板牙磨损后将它磨穿,并借助两个90°沉头孔调整板牙螺纹尺寸,下侧的两个小锥形沉头孔用于夹持板牙。目前使用的圆柱形排屑孔板牙在加工螺纹时产生圈状切屑,并由于…     

应用优选法优选刀具角度

优选法又称0.618法,在生产和科学研究中应用很广泛。在金属切削加工中,刀具角度的选择,运用0.618法省时、省消耗,经济效益显著。最初,我们在铣削不锈钢零件时,选用的刀具主偏角φ=65°,轴向前角γ=-2°,后角α=6°,铣刀转速为900r/min,走刀量s=70mm min。由于不锈钢材料硬而且韧性大,切屑粘刀,加工时常烧刀尖,这样磨刀     

问题解答

[问]使用一般的硬质合金刀具如何加工铬锰钢螺栓?(林尔金)[答]在加工机械强度较高的零件时,没有其它刀具材料的情况下,采用仅有的YT15、YG8,如果发现刀具易崩刃,可以用油石(或砂轮)将刀刃背出负倒棱,把前角加大到10°～15°,使切削轻快。如切屑在刀具顶面不易流出,有粘刀现象,可以适当提高切削速度(v=50～90米/分),加快切屑流速,排屑流畅。如果材料很硬,例如加工调质后的低铬锰钢,刀具上去就磨损,可降低切削速度到v=     

修磨前面的麻花钻

由于标准麻花钻存在一些缺点,在切削刃上各点的前角数值不相等且变化很大,从外缘到钻心处,前角由正30°减到负30°。这样,靠近钻心处前角为很大的负值,切屑形成条件很坏,切削抗力大;而外缘处前角很大,显得刃口薄,强度低,散热条件差,但切削速度相对是最高。所以标准麻花钻外缘拐角处磨损很快,特别是钻削难加工材料时更差。如将麻花钻的前面沿主切削刃进行修磨c(附图),可以有效地提高麻花钻的切削性能和耐用度。这种钻头的几何参数为:前角γ=0°、锋角2(?)=120°、螺旋角ω=30°;钻头的后     

多重基体开裂对平纹编织C/SiC复合材料断裂强度的影响

平纹编织C/SiC复合材料含裂纹试件受拉伸载荷时,裂纹尖端出现垂直于载荷方向的基体开裂损伤带。对试件断口观察,发现拉伸带宽度约等于纤维束宽度;裂纹扩展时,拉伸带内垂直于裂纹面的纤维束形成对裂纹面的桥联。试验结果显示,桥联纤维束出现多重基体开裂的材料断裂强度较高;而纤维束断面平整,未出现多重基体开裂的材料断裂强度相对较低。基于D-B(Dugdale-Barrenblett)模型,研究纤维束多重基体开裂损伤对C/SiC复合材料断裂强度的影响。发现多重基体开裂损伤引起纤维束非线性应力应变关系,能显著提高平纹编织C/SiC复合材料含裂纹件的断裂强度。对于平纹编织C/SiC复合材料,长度参数L0=G/(Fσ20)可以表征材料内桥联机制作用的范围。当裂纹裂纹长度a≥6 mm时,线弹性断裂力学对于平纹编织C/SiC复合材料是适用的。     

表面微织构铣刀切削CFRP的表面加工质量研究

传统铣削加工碳纤维增强复合材料(CFRP)时容易产生表面加工质量缺陷。为改善CFRP表面加工质量,提出在刀具前刀面加工长条状表面微织构,制备出平行于主切削刃(记作PAM)和垂直于主切削刃(记作PEM)两种类型微织构铣刀,进行CFRP端铣试验。与无织构刀具(记作NCM)铣削进行对比试验,对表面粗糙度和表面纤维剪切形貌进行分析研究,揭示两种类型的表面微织构对铣削0°、45°、90°和135°单向纤维铺层CFRP表面粗糙度及剪切方式的作用机理。结果表明:在表面微织构的作用下,PAM和PEM刀具铣削的表面粗糙度值有不同程度的降低,使得切屑纤维的弯曲程度改变,提高刀具对切屑的剪切能力,避免切屑产生的较大弯曲变形导致表面树脂或纤维的剥离。     

用C650车床铣削阿基米德螺旋槽

我厂产品1310/1525硫化机上有一个零件。在它的平面上有8条均布等距的阿基米德螺旋槽。图1为工件示意图,图中仅画出一条槽;槽宽42_(+0.30)~(0.80),深22mm;表面粗糙度R_α12.5.螺旋槽中心线的方程式为p=120+1.3325θ、其中p为极径,θ为极角。0°≤θ≤196°30′。由于我厂不具备加工这种螺旋槽的专用仿形铣,经过分析,可以在C650车床上加工,但车床要作一点小小的改装。一、挂轮计算及改装 1.确定铣刀径向行程按上述方程式p=120+1.3325θ,当θ=0°时,p_1=120mm(起点),当θ=360°时,p_2=599.7mm(终点)。故升程h=599.7-120=479.7mm。     

40CrNiMo精车削模拟

采用有限元软件,使用钢材精加工刀片CNMG120408-PB2对40CrNiMo进行常温下高速车削模拟,通过模拟切削来分析该刀片切屑控制的能力。模拟结果显示,当Vc=280m/min、ap=1.0mm、fn=0.3mm时切屑形状成长螺旋状,并朝工件待加工方向移动,切削力与切削温度都很低。当Vc=280m/min、ap=1.5mm、fn=0.3mm时切屑形状成C字形,切屑朝工件待加工方向移动,切削温度在890℃以下,切削力在1130N左右,切削效果很好。     

Z-pin增强陶瓷基复合材料拉伸性能及损伤研究

研究Z-pin横向增强平纹编织陶瓷基复合材料的拉伸件能及损伤.碳纤维平纹编织物和碳纤维Z-pin制备的预制体,通过化学气相渗透(chemical vapor infiltration,CVI)工艺制成Z-pin增强平纹编织陶瓷基复合材料.采用单轴拉伸试验及加一卸载试验研究材料拉伸力学性能参数及破坏机理.结果表明,Z-pin嵌入引起的面内纤维断裂、损伤以及弯曲变形,降低了平纹编织陶瓷基复合材料的抗拉强度;Z-pin增强平纹编织陶瓷基复合材料抗拉应力应变曲线具有非线性特性;卸载再加载过程中损伤基本没有增加,残余应变与卸载应力成二次关系,卸载模量与卸载应力成Boltzmann关系.     

Study on burr occurrence and surface integrity during slot milling of multidirectional and plain woven CFRPs

Machining carbon fiber reinforced composite (CFRP) is often accompanied with cutting edge defects and surface damage including interlayer delamination, cavities and debonding of fiber-matrix. A detailed understanding of the effect of fiber configuration and cutting parameters on cutting force, burr occurrence/formation and surface integrity is necessary. In this paper, experimental data is presented relating to fiber burrs on entry surface, cutting force, surface roughness and workpiece integrity when slot milling CFRP laminates with varying fiber configurations (0°/90°, 45°/135° and plain woven) at different cutting speed (60 and 120 m/min) and feed rate (0.05 and 0.1 mm/rev). Lateral cutting force is recorded down to 56 N and highly dependent on fiber orientation. The length (up to ~?5.6 mm) and amount of fiber burrs are highly related to fiber orientation and fiber cutting angle. Surface roughness Ra down to ~?1.4 μm was recorded when milling type 2 (45°/135°) and type 3 (plain woven) laminates. Various surface defects predominantly occurred due to different cutting conditions and fiber configurations, which are mainly located in the layers with fibers orientated at 45°/135°. The occurrence and propagation of fiber burrs and surface cavities were also investigated based on different fiber fracture mechanisms.     

Effect of tool vibration on chip formation and cutting forces in the machining of fiber-reinforced polymer composites

This article investigates the chip formation mechanism and its influence on cutting forces during the elliptic vibration-assisted (EVA) cutting of fiber-reinforced polymer composites. To clarify the effect of the vibration, systematic finite element and experimental studies were performed on both the EVA and the traditional cutting of unidirectional fiber-reinforced polymers with various fiber orientations. The key factors that govern the cutting forces have been taken into account, such as the depth of cut, feed rate, tool vibration frequency and amplitude. The study found that fiber orientation significantly affects the chip formation and cutting forces. Fiber fracture can happen either above or below the trimming path, but that above the path dominates chip formation. When a fiber orientation is less than 90°, chipping is mainly through bending-induced fracture of fibers; when it is beyond 90°, however, chipping is mostly by crushing the fracture of fibers. Compared with a traditional cutting process, the EVA cutting can minimize the fiber orientation effect through localized fiber fracture. A dimensional analysis was then performed to provide a quantitative prediction of the cutting forces.     

圆渐开线变截面涡旋压缩机几何性能综合分析

提出一种由不同基圆半径的圆渐开线组成的新型变截面涡旋压缩机型线，组成形式为圆渐开线Ⅰ+圆渐开线Ⅱ+圆渐开线Ⅰ。论述型线的生成方法，给出型线的一般方程，建立一系列圆渐开线变截面涡旋压缩机的几何模型。针对建立的几何模型，分析控制系数θ、φ^*、R_or对变截面涡旋压缩机几何性能的影响。以圆渐开线Ⅰ为基础，构建圆渐开线Ⅰ+高次曲线+圆渐开线Ⅰ的变截面涡旋压缩机的几何模型，综合分析两类变截面涡旋压缩机的几何性能。结果表明：θ取中值θ_M，φ^*，控制系数R_or取较大值，对应的几何性能较优。高次曲线变截面涡旋压缩机与中值θ_M对应的圆渐开线变截面涡旋压缩机相似，可相互替代。     

弹光调制测椭偏参量的数字锁相数据处理

为了实现椭偏参量ψ和Δ的高速、高灵敏测量,建立了一种测量成本低、重复性好和便于工业化集成的椭偏测量方案。本文对弹光调制型椭偏参量测量系统进行了原理分析,针对弹光调制器的工作模式及调制光信号特点,设计了基于现场可编程门阵列的数字锁相数据处理方案。现场可编程门阵列提供弹光调制器工作的信号源,并控制AD采样;同时产生正弦和余弦参考序列,并完成直流项、一倍频项和二倍频项的同相分量和正交分量的提取,进而求解出椭偏参量。利用搭建的试验系统对SiO2薄膜厚度为3.753nm的硅片样品进行了实验分析。实验结果表明,采样时间为20ms时,椭偏参量ψ和Δ的平均值分别为9.622°和168.692°,标准偏差分别为0.005°和0.008°;采样时间设置为200ms时,椭偏参量测量平均值与20ms的非常接近,标准偏差减小,并且都在0.001°量级,揭示了本系统具有较高的灵敏度和较好的重复性。     

厚截面碳纤维复合材料远表面微缺陷超声检测

为了识别厚截面碳纤维复合材料(CFRP)远表面的微缺陷,使用递归分析方法对超声检测信号进行分析。首先在厚截面CFRP材料上打孔以模拟微缺陷,采用水浸超声脉冲反射法对不同大小的模拟缺陷进行检测。然后选取缺陷位置附近信号段,确定嵌入维数m、延迟时间τ、阈值ε等参数,对各信号段进行递归分析,得到递归图及递归定量分析结果。比较无缺陷信号和有缺陷信号的递归图,从宏观上定性确定微缺陷对超声信号的影响;比较无缺陷信号和有缺陷信号的递归定量分析结果,根据每个递归定量参数的物理意义,对缺陷产生的影响作出合理的解释。最后,使用不同中心频率探头进行实验,确定合适的探头参数。分析结果表明,使用7.5MHz高分辨率超声探头时检测效果最好;当嵌入维数为7、延迟时间为2、阈值为2时,递归图中出现异常白色区域、递归点增多且对角线结构变长,同时所选取的递归定量参数随缺陷增大而上升,表明厚截面CFRP远表面超声信号可能存在混沌结构,而微缺陷的存在会改变原有信号结构。所研究内容为实际微缺陷的定量识别及分类打下基础。     

光栅复制拼接光路中入射光角度对拼接误差的影响

设计了一种基于干涉检验法的复制拼接光栅测量光路。针对光栅复制拼接光路中入射光角度难以精确测量的问题,分析了光栅拼接实验中入射光角度对光栅拼接的影响。建立了光栅拼接误差模型,分析了五维拼接误差的容限要求。按照光栅复制拼接光路的要求,设计了一种干涉仪角度调节装置。根据误差模型和拼接光路分析了500mm×500mm大尺寸中阶梯光栅复制拼接光路中入射光角度误差与拼接误差的关系。结果显示:入射光角度误差为1°,拼接光路中绕x轴,y轴的转动误差Δθx,Δθy和沿z轴的位移误差Δz的计算值与实际值之间分别相差0.002 1μrad,0.003 3μrad和0.348 2nm时,引起波前差为2.590 1nm。根据这一计算结果,给出了干涉仪角度调节装置的设计指标,即设置角度调节分度为0.1°时,可满足大尺寸光栅复制拼接要求。     

Influence of fiber orientation on abrasive wear of unidirectionally reinforced carbon fiber–polyetherimide composites

A composite with continuous carbon fibers (CF) (80% by vol.) and high performance thermoplastic polyetherimide (PEI) matrix was developed and evaluated for various mechanical properties as a function of fiber orientation angle (0°, 30°, 45°, 60° and 90°). It was observed that Young's modulus, Poisson's ratio, toughness and % strain decreased with the increase of fiber orientation angle with respect to loading direction. In-plane shear modulus was highest for fibers with 45°. Overall, unidirectional (UD) CF reinforcement enhanced all strength properties of PEI significantly. Composites with fibers in 0° (parallel to loading direction) proved best in almost all the properties. Tribological evaluation in abrasive wear mode under different loads and fiber orientations indicated that coefficient of friction (μ) and specific wear rate (K₀) decreased with load, in general. Comparatively low specific wear rate (K₀), (in the order of 0.7 1×10^?9 m³/Nm) was observed for 0° fiber orientation, while fibers in 90° showed almost three times higher wear rate. Overall fiber reinforcement in 0° orientations proved beneficial from both strength and tribological performance point of view. SEM proved useful to correlate wear rate with surface topography.     

Investigate on milling force of cryogenic cooling processing aluminum honeycomb treated by ice fixation

Aerospace metal honeycomb materials with low stiffness had often the deformation, burr, collapse, and other defects in the mechanical processing. They were attributed to poor fixation method and inapposite cutting force. This paper presented the improvement of fixation way. The hexagonal aluminum honeycomb core material was treated by ice fixation, and the NC milling machine was used for a series of cryogenic machining. Considering the similar structure of fiber-reinforced composite materials, the milling force prediction model of ice fixation aluminum honeycomb was established, considering tool geometry parameters and cutting parameters. Meanwhile, the influence rule on milling force was deduced. The results show that compared with the conventional fixation milling method, the honeycomb processing effect is improved greatly. The machining parameters affect order on milling forces: the cutting depth is the most important, followed by the cutting width, then the spindle speed and the feed. Moreover, too small cutting depth (a_p?=?0.5 mm) will cause insufficient cutting force, while a_p?>?2 mm with higher force will reduce the processing quality of honeycomb. Simultaneously, the honeycomb orientation (θ) has a great influence on processing quality. Using the model, the predicted and measured error values of the feed and main cutting force are all small in θ?<?90°. But, the rate is 33 and 26% for the main cutting force and feed force error in θ?>?90°, respectively, while they all exhibit the smallest error in θ?=?60°. This bigger error mainly is due to unstable cutting force with obtuse angle. In addition, the tool rake angle has little influence on cutting quality in θ?<?90°, but bigger on that in θ?>?90°. Furthermore, the calculation model successfully conforms to the main deformation mechanism and influences parameters of the cutting force in the milling process, and it can accurately predict the cutting force in θ?<?90° and guide the milling process.     

Effect of thermal properties on laser cutting of continuous glass and carbon fiber-reinforced polyamide 6 composites

The single mode fiber laser cutting of two types of continuous fiber-reinforced thermoplastic composites (TPC) with polyamide 6 (PA6) matrix and a fiber content of 60 wt% was investigated: a glass fiber-reinforced composite (PA6/GF60) and a carbon fiber-reinforced composite (PA6/CF60). Preliminary, the thermal properties of the composites were analyzed to derive the cutting mechanisms. Thermogravimetric Analysis (TGA) showed decomposition onset temperatures of 457.6°C for the PA6 matrix and 737.3°C for the carbon fibers, while no thermal decomposition of the glass fibers was detected up to 1,000°C. In consequence, the single mode fiber laser cutting of the PA6/GF60 composites required a significantly higher number of cutting cycles in conjunction with an increased heat affected zone (HAZ) as compared to the PA6/CF60 composites. Analysis of the HAZ and the mechanical properties of the laser cut composites by optical microscopy and uniaxial tensile testing showed an anisotropy and dependency on the laminate structure. However, the obtained mechanical properties of the laser cut composites were found comparable to their water jet cut counterparts.