Interface and performance of 3D printed continuous carbon fiber reinforced PLA composites

A novel 3D printing based fabrication process of Continuous Fiber Reinforced Thermoplastic Composites (CFRTPCs) was proposed. Continuous carbon fiber and PLA filament were utilized as reinforcing phase and matrix, respectively, and simultaneously fed into the fused deposition modeling (FDM) 3D printing process realizing the integrated preparation and forming of CFRTPCs. Interfaces and performance of printed composites were systematically studied by analyzing the influencing of process parameters on the temperature and pressure in the process. Forming mechanism of multiple interfaces was proposed and utilized to explain the correlations between process and performance. Fiber content of the printed specimens can be easily controlled by changing the process parameters. When the fiber content reached 27%, flexural strength of 335 MPa and modulus of 30 GPa were obtained for the printed composite specimens. Composite components were fabricated to demonstrate the process feasibility. Potential applications could be found in the field of aviation and aerospace.     

The thermal expansion of carbon fibre reinforced plastics

Measurements of the principal linear thermal expansion coefficients of a tridirectional (–45°, 0°, +45°) carbon fibre reinforced plastics laminate are reported in the approximate temperature range 90 K to 500 K. A quantitative evaluation of the in-plane results in thermoelastic terms has yielded an agreement with these results consistent with the approximations and uncertainties involved. The qualitative agreement with expectations based upon the behaviour of unidirectional and bidirectional laminates is also demonstrated. The account concludes with an examination of some effects which are peculiar to multidirectional laminates.     

A comprehensive study on the equivalent electrical conductivity tensor validity for thin multidirectional carbon fibre reinforced plastics

The electrical conductivity of the dry carbon fibre multidirectional thin layers (without resin matrix material) can be expressed by an equivalent EC tensor. The flow of the electric current inside the material is depended, mainly, upon the material’s microstructure and specifically upon the interlaminar microstructure. In the case of the multidirectional carbon fibre composites, two different methodologies were used in order to elucidate the EC behaviour of the multidirectional laminates both quantitatively and qualitatively. The first experimental setup was used in order to compare the measured electrical resistance to the calculated equivalent EC tensor. Also, the temperature field changes according to the equivalent EC tensor of each laminate and the second methodology was utilized in order to elucidate the validity of equivalent EC tensor indirectly, comparing the temperature field of the electro-thermal numerical models and the measured temperature field.     

Interlaminar fracture micro-mechanisms in toughened carbon fibre reinforced plastics investigated via synchrotron radiation computed tomography and laminography

Synchrotron Radiation Computed Tomography (SRCT) and Synchrotron Radiation Computed Laminography (SRCL) permit 3D non-destructive evaluation of fracture micro-mechanisms at high spatial resolutions. Two types of particle-toughened Carbon Fibre Reinforced Polymer (CFRP) composites were loaded to allow crack growth in Modes I and II to be isolated and observed in standard and non-standard specimen geometries. Both materials failed in complex and distinct failure modes, showing that interlaminar fracture in these materials involves a process zone rather than a singular crack tip. The work indicates that incorporating particle/resin, fibre/interlayer and neat resin failure is essential within models for material response, since the competition between these mechanisms to provide the energetically favourable crack path influences the macro-scale toughness. The work uniquely combines the strengths of SRCT and SRCL to compare failure micro-mechanisms between two specimen geometries, whilst assessing any edge effects and providing powerful insight into the complex micro-mechanical behaviour of these materials.     

International developments in fibre reinforced plastics for anti-corrosion uses

An earlier RAPRA market survey on fibre-reinforced plastics had indicated that the anti-corrosion was the fastest growing in the U.K. In view of the obvious interest in this field a follow-up devoted exclusively to the subject was promoted.The factors for and against the use of GRP in process plant are considered, together with an assessment of their performance record, Developments in materials, products and processes over more recent years were assessed, following a literature search and a fall-off in consumption over the last two years (contrary to earlier forecasts) is attributed to the general decrease in capital investment programmes. Increases in raw materials prices have also contributed to this by bringing GRP prices closer to those of stainless steel, whilst glass flake linings are also replacing those of GRP in this particular process.Despite this, anti-corrosion applications show a faster than average growth rate compared with those in other sectors.     

Selection of drilling conditions for glass fibre reinforced plastics

An experimental investigation has been carried out into the drilling of glass fibre reinforced plastics using HSS twist drills. A test series was conducted using a wide range of cutting conditions and drill geometry, namely cutting speed, feed rate, point angle and helix angle. Decisions relating to the ‘optimum’ drilling conditions were based on the geometrical accuracy and appearance of the produced holes. Drill wear was measured during the test trials and used as a further constraint in ‘optimum’ cutting conditions selection. Speed, feed rate and drill point angle were found statistically to be the most significant parameters influencing hole quality. Drill wear can be successfully correlated to the level of the thrust force. A simple nomogram is included to predict drill wear level from the thrust level or the amount of material removed.     

The influence of voids on the hydrothermal response of carbon fibre reinforced plastics

Measurements are reported of the shear modulus, strength and strain at failure of carbon fibre reinforced plastics exposed to the effects of temperature and temperature plus water. Two types of specimen were employed, one with a low void content and one with a high void content. Properties were determined either at room temperature after specimens had been fully dried, or at high temperature and in some cases at high temperature and under water. For good, low void content specimens, any effects of temperature and water were completely removed by drying. For specimens containing more than 1 vol% voids this was not so. Measurements at high temperature indicated a fall-off in stiffness and strength for either type of specimen, and for void containing specimens an increase in the strain at failure indicative of bond disruption. The added effects of water were complex.     

碳纤维增强环氧树脂复合材料与铝板胶螺混合连接接头失效仿真

基于商用有限元软件ABAQUS,建立了碳纤维增强环氧树脂复合材料（CFRP）层合板和铝板双搭接胶螺混合连接接头强度预测模型,并进行了仿真分析,同时与试验结果进行对比,探究了此类混合接头在拉伸载荷工况下的失效形式和承载能力。结果表明,拉伸加载过程中,螺栓通过分担部分载荷加强了胶接连接。混合接头的失效形式先表现为胶层的断裂失效,最终表现为层合板孔边挤压失效。利用模型预测的接头承载能力与试验结果的误差为9.7%,具有较好的吻合性。该分析方法能够为复合材料-金属胶螺混合连接的分析和设计提供一定的参考。      

Tests of continuous concrete slabs reinforced with carbon fibre reinforced polymer bars

Although several research studies have been conducted on simply supported concrete elements reinforced with fibre reinforced polymer (FRP) bars, there is little reported work on the behaviour of continuous elements. This paper reports the testing of four continuously supported concrete slabs reinforced with carbon fibre reinforced polymer (CFRP) bars. Different arrangements of CFRP reinforcement at mid-span and over the middle support were considered. Two simply supported concrete slabs reinforced with under and over CFRP reinforcement and a continuous concrete slab reinforced with steel bars were also tested for comparison purposes. All continuous CFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. It was also shown that increasing the bottom mid-span CFRP reinforcement of continuous slabs is more effective than the top over middle support CFRP reinforcement in improving the load capacity and reducing mid-span deflections. The ACI 440.1R–06 formulas overestimated the experimental moment at failure but better predicted the load capacity of continuous CFRP reinforced concrete slabs tested. The ACI 440.1R–06, ISIS–M03–07 and CSA S806-06 design code equations reasonably predicted the deflections of the CFRP continuously supported slabs having under reinforcement at the bottom layer but underestimated deflections of continuous slabs with over-reinforcement at the bottom layer.     

碳纤维增强受电弓滑板的性能表征

采用改性酚醛树脂为粘结剂,连续碳纤维和短切纤维为增强相,铜为导电相,石墨为润滑相,利用热压技术制备碳纤维增强受电弓滑板.对试样进行电阻测试、冲击试验以及磨损试验,利用SEM对冲击断面和磨损形貌进行观察.结果表明,连续碳纤维增强滑板的冲击性能和耐磨性明显优于短切纤维增强滑板;碳纤维含量对滑板的机械性能影响较大;纤维与树脂...     

碳纤维增强复合材料T型齿槽加工缺陷的形成机制

针对平纹编织碳纤维增强复合材料(CFRP)T型齿槽切出侧最外层纤维在切制过程中产生的缺陷,建立齿槽切出侧最外层纤维的切削模型,采用T型铣刀展开切制齿槽的试验,研究缺陷的形成机制。在切出侧最外层纤维的切削过程中,存在A、B两种情形,分别为纬向纤维的切削有经向纤维的支撑和无经向纤维的支撑。结果表明: 随着每齿进给量的增大,齿槽切出侧最外层纤维的残余因子基本呈减小趋势,而分层因子呈增大趋势,且残余因子主要经历2次减小,依次包括A情形残余纬向纤维的减少和残余经向纤维的减少;B情形的残余纬向纤维普遍存在于每次试验中,但在A情形纤维被切除的适当每齿进给量区间内,部分B情形纤维能有效被切除;此外,采用细晶粒硬质合金刀具进行齿槽加工的每齿进给量选择在11.22 μm/z~15.62 μm/z区间内较为合适。试验结果与理论推导所反映的规律基本一致,该研究对每齿进给量的选取和缺陷的抑制具有指导意义。     

The crack evolution on the atomistic scale during the pyrolysis of carbon fibre reinforced plastics to carbon/carbon composites

The development of the crack patterns during the pyrolysis of carbon fibre reinforced plastics (CFRP) to carbon/carbon composites as the second manufacturing step in the liquid silicon infiltration (LSI) process was investigated. In the basic examination reported previously, it was discovered that a substantial amount of cracking occurs beyond 650 °C, when the mesoscopic crack pattern has already fully developed. This additional cracking could not be visualized by using standard microscopy. Thus additional investigations were conducted by using conventional and high-resolution transmission electron microscopy to obtain information on the atomistic scale on the assumed cracking activity.It was found that the crack development starts at pores that develop as a compensation for the rough fibre surface. Crack propagation takes place by evolution of new nanoscopic cracks caused by fibre–matrix-debonding in the tensile stress field in front of the crack tip and subsequent connection with the main crack. Thus the interconnection mechanism – cracking as the connection of cracks on a subordinated scale to form a new crack – is the second main cracking mechanism beside transversal cracking (leading to a regular mesoscopic crack pattern) active during the carbonization of CFRP components.     

碳纤维织物复合材料螺柱-柱销连接结构研究

在综合分析各种复合材料连接结构的基础上,针对复合材料构件高承载轴向连接要求,提出了织物复合材料螺柱-柱销连接结构,并实验研究了织物复合材料的挤压强度,测试了螺柱-柱销连接结构的承载能力.试验结果表明,织物复合材料的最大挤压强度为887 MPa,高于0/90纤维层板复合材料的挤压强度;织物复合材料螺柱-柱销连接结构在薄壁复合材料构件的轴向连接方面,与传统的金属端框连接形式相比,接头质量效率高,成型工艺简便,具有较大的应用潜力.     

碳纤维增强树脂基复合材料预紧力单齿接头的静态及疲劳性能试验

通过试验研究了预紧力、齿长和载荷水平对碳纤维增强树脂基复合材料（CFRP）预紧力单齿接头（PTSTC）静态和疲劳性能的影响。试验结果表明:CFRP PTSTC的疲劳极限承载力可以达到静态极限承载力的80%~85%,与螺栓等传统连接方式相比,其疲劳性能具有一定优势;预紧力可以显著改善CFRP单齿接头的静态和疲劳性能;CFRP PTSTC的静态极限承载力随齿长增加而升高,但是在相同载荷水平下增加齿长不一定可以延长接头的疲劳寿命,尤其是在低载荷水平下齿长增加反而会缩短疲劳寿命;在加载初期,PTSTC的疲劳裂纹快速萌生,之后扩展缓慢,在接近破坏前的几次循环中又骤然增大,预紧力可以减缓疲劳损伤的累积速率;疲劳过程中PTSTC的刚度衰退不明显,在前95%疲劳寿命阶段仅下降1%~4%,预紧力也可以减缓刚度的衰退速率。所得研究成果可为复合材料接头抗疲劳设计提供参考依据。      

连续碳纤维混合3D打印工艺及仿生腿性能研究

基于连续与短切碳纤维复合材料双喷头混合3D打印工艺原理,本文研究了连续碳纤维在实验样条中的排布方式,对3D打印中连续碳纤维的层间布局进行工艺规划,并应用于四足机器人仿生腿的制造,以增强四足机器人仿生腿的承载能力。根据不同工况下四足机器人仿生腿的受力分析及静力学仿真结果,得到仿生腿受力时理论应力集中部位,并由此设计承载力实验对仿生腿30°外展工况持续施加力至额定载荷;通过仿生腿在承载力实验中结构失效的部位与仿真时理论应力集中处的对照分析,证明了仿真结果的准确性。依据仿生腿侧面受力时结构失效的测试评估结果,对3D打印仿生腿中的连续碳纤维的布局进行合理工艺规划,在不增大连续碳纤维整体含量的条件下对应力集中部位进行选择性增强,可在提高3D打印性价比的同时使仿生腿的最大拉升强度提升至310 MPa,从而达到更优的承载作用。     

Infrared stress measurements of thermal damage to laser-processed carbon fiber reinforced plastics

Recently, the laser processing of carbon fiber reinforced plastics (CFRPs) has attracted attention owing to the high processing speed and less tool wear. A problem in the laser processing of CFRPs is the lower strength than that of CFRPs processed by machines. This is considered to be due to the heat-affected zone (HAZ) generated during laser processing. In this study, the stress distributions of CFRPs processed by a laser obtained was evaluated by using infrared thermography. X-ray CT images were also obtained, which enabled us to discuss the stress distribution in terms of the HAZ. The stress distribution showed that the area with reduced stress generated in the HAZ which was introduced by laser processing. The region of low stress in the HAZ was visualized by infrared thermography. It is shown that the regions with reduced stress induce the conventionally reported decrease in strength of laser-processed CFRPs.     

Bending fracture rule for 3D-printed curved continuous-fiber composite

Three-dimensional (3D) printing is an attractive technology to produce complex structures without the need for expensive tools and molds. Additives are usually incorporated with the plastic materials used in 3D printing to increase their strength and rigidity. In particular, carbon fiber-reinforced plastic (CFRP) shows promise as a material for use in 3D printing. However, the strength of CFRP after printing is still unclear, although it is known that its strength is affected by the plastic melting during printing. In this study, we analyzed the fracture behavior of CFRP specimens before and after bending to different curvature radii. From the experimental results, a fracture criterion that described the behavior of the materials by considering tensile and compressive loads was developed. The fracture mechanism was the same for CFRP specimens with different curvature radii. These results increase our understanding of the mechanical properties of CFRP materials used in 3D printing.     

Ductility of 3D printed concrete reinforced with short straight steel fibers

ABSTRACT

With the number of 3D printed concrete structures rapidly increasing, the demand for concepts that allow for robust and ductile printed objects becomes increasingly pressing. An obvious solution strategy is the inclusion of fibers in the printed material. In this study, the effect of adding short straight steel fibers on the failure behaviour of Weber 3D 115-1 print mortar has been studied through several CMOD tests on cast and printed concrete, on different scales. The experiments have also been simulated numerically. The research has shown that the fibers cause an important increase in flexural strength, and eliminate the strength difference between cast and printed concrete that exists without fibers. The post-peak behaviour, nevertheless, has to be characterised as strongly strain-softening. In the printed specimens, a strong fiber orientation in the direction of the filament occurs. However, this has no notable effect on the performance in the tested direction: cast and printed concrete with fibers behave similarly in the CMOD test. For the key parameters, no scale effect was found for the specimens with fibers, contrary to the ones without. Numerical modelling of the test by using the Concrete Damage Plasticity material model of Abaqus, with a Thorenfeldt-based constitutive law in compression and a customised constitutive law in tension, results in a reasonable fit with the experimental results.     

C_f/Mg复合材料的热膨胀系数及其理论计算

采用负压浸渗-液固挤压法制备了定向短切碳纤维(aligned Csf)及穿刺-2D碳纤维织物(2.5DCf)增强镁合金复合材料,观察了两种复合材料的微观组织结构,测定了其在30～350℃范围的热膨胀系数(α),并在Schapery模型的基础上提出了计算定向Csf/Mg复合材料及2.5DCf/Mg复合材料α值的修正模型。结果表明,在30～200℃范围内,两种Cf/Mg复合材料的α值均表现出随温度的升高而升高的趋势,但在超过250℃以后,α值出现降低或稳定的现象,其原因为随着温度的升高,铝元素固溶度的增大、基体发生部分塑性变形等因素导致的;提出的修正模型理论计算值与其相应的实验测试α值之间的误差均在5%之内,表明该修正模型能够有效预测实验中的α值。