Dynamic fracture toughness of polypropylene reinforced with cellulose fiber

To better understand mechanisms of fracture under impact loading in cellulose-reinforced polypropylene, dynamic fracture analysis was performed based on linear elastic fracture mechanics. Dynamic critical energy release rates and dynamic critical stress intensity factors were deduced from instrumented Charpy impact test measurements. Dynamic fracture toughness increased with cellulose content. However, the assumption of linear elasticity began to break down for cellulose fiber contents exceeding 40% by weight. Scanning electron microscopy showed considerable fiber curl in the composites, especially at low fiber contents; at high fiber contents, composites developed a three-layer structure.     

Dynamic simulation of microstructure and rheology of fiber suspensions

A numerical simulation method has been developed to predict the motion of fiber suspensions in various flows by using the particle simulation method (PSM), in which a fiber is modeled by an array of spheres. The hydrodynamic interaction among fibers is considered by decomposing into intra-fiber and inter-fiber interactions. For the intra-fiber case, the many-body problem is solved by calculating the mobility matrix for each fiber to obtain the hydrodynamic force and torque exerted on each sphere. For the inter-fiber case, only the near-field lubrication force is considered between spheres belonging to different fibers. The methodology was applied to predicting the microstructure and rheological properties of rigid fiber suspensions in simple shear flow and fiber orientation in two-dimensional diverging flow by combining this method with the finite element method (FEM). In the former, the overshoot of suspension viscosity, due to the transient change of the microstructure, was observed in semi-dilute to concentrated systems. In the latter, the calculated fiber orientations agreed with expectations of theory.     

基于两相模型的聚合物流动诱导结晶数值模拟

基于两相流动诱导结晶模型,采用谱方法分别计算无定形相的构象张量分布函数和半晶相的取向张量分布函数,进而根据Avrami方程和晶核成核速率与第一法向应力差的关系计算成核速率和结晶度。预测剪切对体系结晶速度的影响,并模拟了活化晶核数目和晶体取向的演化。计算结果表明,剪切对聚合物的结晶动力学性能有显著的影响,但是剪切对聚合物结晶的加速作用不是无限制的,随着剪切强度的增加,对结晶加速作用会变得不再明显。     

Dynamic simulation of multicomponent distillation

A program has been developed for the dynamic simulation of large scale chemical processes. The simulator has a highly modular structure and an explicit integration routine which is capable of handling large systems of stiff ordinary differential equations. The use of an explicit method reduces computer storage requirements and greatly simplifies the writing of new modules. Unit subroutines have been written which are capable of describing multicomponent distillation columns without resorting to conventional thermodynamic equilibrium calculations. The absence of these iterative routines reduces computation time and allows tray efficiencies to be handled in a more natural manner than is possible with Murphee efficiencies. The program also includes an advanced thermodynamic property package based on the Peng Robinson equation of state. An industrial process consisting of two distillation columns with a combined total of seventy-five mass transfer stages, has been successfully simulated and the computed results have been compared with dynamic data collected from plant tests.     

Fatigue fracture of long fiber reinforced nylon 66

The fatigue behavior of long fiber reinforced nylon 66 has been investigated by measuring fatigue crack propagation rates of injection molded samples. Plaques varying in thickness from 3 to 10 mm were employed for nylong 66 containing either glass, carbon or aramid fibers. Both conventional chopped, short fiber reinforcements and pultruded long fiber filled nylon 66 were examined. Long fiber reinforced nylon 66 exhibits improved fatigue resistance as shown by decreases in fatigue crack propagation rates compared to short fiber filled composites. Using a fracture mechanics analysis, it is shown that the improvements are due primarily to the higher moduli of the long fiber reinforced nylon 66, with only a slight increase in the calculated strain energy release rate associated with fatigue crack growth. For short or long glass fibers, and for short carbon fibers, the effects of fiber orientation on fatigue crack growth rates can be predicted from the fracture mechanics model. More significant effects of fiber length on fatigue fracture energies are noted for long aramid and long carbon reinforced nylon 66. It is also shown that thicker plaques can exhibit poorer fatigue fracture behavior owing to their inferior core sections.     

高性能纤维扭转疲劳断裂研究

在自制的扭转疲劳装置上,进行对位芳纶和超高相对分子质量聚乙烯(UHMWPE)纤维扭转疲劳实验,分析扭转机理及其扭转疲劳断口形貌特征。结果显示,相同条件下,UHMWPE纤维的耐扭转疲劳性能优于对位芳纶。对位芳纶扭转疲劳断口呈现原纤分裂,UHMWPE纤维皮层呈蠕变特征,芯层有脆性断裂特征。     

纤维悬浮聚合物熔体中纤维影响的数值模拟

采用一种多尺度模型研究了纤维悬浮聚合物熔体的流动过程,通过宏观流体的流动状态、纤维所在尺度上的纤维取向表征和聚合物溶液大分子哑铃模型尺度上的哑铃概率分布三尺度信息,实现了纤维悬浮聚合物熔体流动控制方程和本构关系的三尺度共同表征。使用SIMPLER-FDMS算法对多尺度控制方程组进行了求解,并通过4∶1等温平板收缩流的数值模拟验证了该多尺度模型的有效性。通过对纤维浓度、纤维间相互作用以及纤维长径比的分析,研究了纤维参数对聚合物基熔体悬浮体系及纤维取向的影响。     

Disentanglement decelerating flow-induced nucleation

With three polymers (poly(1-butene), isotactic polypropylene and syndiotactic polypropylene) as model systems, the effect of extensional strain on the nucleation rate was studied using a home-made miniature extensional rheometer and in-situ X-ray scattering. A non-monotonic correlation between nucleation rate and strain is observed around rheological yield point. Increasing strain leads to an increase in nucleation rate as expected when strain is smaller than yield strain, however, it results in a decrease in nucleation rate when strain slightly exceeds yield. We proposed that disentanglement occurs at yield point and thus decelerates flow-induced nucleation. Disentanglement provides freedom for chains to retract and leads to a dissipation of the energy initially imposed by extensional flow, which consequently weakens the effect of flow field on the enhancement of nucleation.     

Dynamic mechanical analysis of fiber reinforced composites

Dynamic mechanical and thermal properties were determined for unidirectional epoxy/glass composites at various fiber orientation angles. Resonant frequency and relative logarithmic decrement were measured as functions of temperature. In low angle and longitudinal specimens, a transition was observed above the resin glass transition temperature which was manifested mechanically as anadditional damping peak and thermally as a change in the coefficient of thermal expansion. The new transition was attributed to a heterogeneous resin matrix induced by the fiber. The temperature span of the glass-rubber relaxation was found to broaden with decreasing orientation angle, reflecting the growth of fiber contribution and exhibiting behavior similar to that of Young's modulus. The change in resonant frequency through the glass transition was greatest for samples of intermediate fiber angle, demonstrating behavior similar to that of the longitudinal shear modulus.     

扁平纤维熔融纺丝动力学模型

根据熔融纺丝的基本原理,推导了扁平纤维的动力学模型。根据所建立的模型,模拟了纺丝工艺条件对纤维异形度的影响。模拟的结果表明:扁平纤维的异形度随着纺丝温度及特性黏度的升高而降低;泵供量一定时,纺速对异形度的影响不大;纺丝速度一定,异形度随着泵供量的增大而增大;吹风条件对异形度的影响较大;随着喷丝孔的长宽比的增大,异形度增加的幅度也较大;异形度在纺程上较小的区间内有明显的下降趋势,并随着泵供量的增加其下降的趋势变缓。     

Numerical simulation of fiber orientation distribution in round turbulent jet of fiber suspension

The Reynolds averaged Navier–Stokes equation was solved numerically with the Reynolds stress model to get the mean fluid velocity and the turbulent kinetic energy in a round turbulent jet of fiber suspension. The fluctuating fluid velocity was described as a Fourier series with random coefficients. Then the slender-body theory was used to calculate the fiber orientation distribution and orientation tensor. Numerical results of mean axial velocity and turbulent shear stress along the lateral direction were validated by comparing with the experimental ones. The results show that most fibers are aligned with the flow direction as they go downstream, and fibers are more aligned with the flow direction within the region near the jet core. The fibers with high aspect ratio tend much easier to align with the flow direction, and the fiber orientation distribution is not sensitive to fiber aspect ratio when fiber aspect ratio is larger than 5. Fiber density has no obvious influence on the fiber orientation distribution and fiber orientation tensor. The randomizing effect of turbulence is insignificant in the regions near outside and jet core, and becomes significant in the region between outside and jet core. The randomizing effect increases with the increasing of the distance from the jet exit. Different components of fiber orientation tensor show a similar distribution pattern.     

Mixed-mode fracture behavior of glass fiber reinforced polymer concrete

Fracture toughness of chopped strand glass fiber reinforced particle-filled polymer composite beams was investigated in Mode I and Mode III loading conditions using three-point bend tests. Effects of crack angles on fracture behavior were also studied. The specimens, which have inclined crack at an angle θ to the axis of the specimens, were used to carry out the tests. The specimens were tested with inclination angles 30°, 45°, 60° and 75°. The results are compared with the values of K_IC obtained using conventional (θ=90° ) specimens. In addition, J integrals were also determined. J_IC increases continuously with increasing in crack angle from θ=30° to θ=90°. In contrast, J_IIIC decreases with the crack inclination angle θ from 30° to 90°.     

The application of fracture mechanics to short fiber composites

The fracture performances of three short glass fiber-reinforced polymer composite systems, PET with 30 wt% glass, nylon 6/6 with 33% glass fibers, and a nylon 6 and 6/6 copolymer with 33% glass, have been characterized using both standard mechanical characterization and fracture mechanics. These results have been compared to fracture tests of an experimental chair base. None of the characterizing techniques was successful in predicting the chair base fracture performances of the materials when the tests were conducted on standard 3-mm-thick test specimens. When larger specimens with comparable morphologies to the chair base were tested, the fracture mechanics tests compared favorably to the chair base fracture tests while the tensile test results were inconsistent in their predictive ability. The findings emphasize the importance of testing laboratory specimens that are similar in morphology to the final part and suggest that fracture mechanics methodologies can be used in materials selection of glass reinforced systems for structural applications. However, for quantitative design, it is necessary to address issues regarding the nature of the inherent flaw in the finished parts.     

The fracture properties of a smart fiber metal laminate

This paper investigates the interfacial, tensile, and fatigue properties of a novel smart fiber‐metal laminate (FML) based on a nickel‐titanium (Ni‐Ti) shape memory alloy and a woven glass fiber reinforced epoxy. Initial tests, using the single cantilever beam (SCB) geometry, have shown that this unique system offers high values of metal‐composite interfacial fracture toughness. Tensile tests have shown that the mechanical properties of these FMLs lie between those offered by its constituent materials and that their tensile modulus and strength can be easily predicted using a rule of mixtures approach. Tension‐tension fatigue tests have shown that the fatigue performance of notched smart FMLs is superior to that offered by the plain Ni‐Ti alloy. A subsequent optical examination of unnotched laminates tested to failure under tension‐tension fatigue loading has shown that the fracture mechanisms occurring within the Ni‐Ti FMLs are strongly dependent on the applied cyclic stress. POLYM. COMPOS., 28:534–544, 2007. © 2007 Society of Plastics Engineers     

Essential fracture work of short fiber reinforced polymer blends

Short glass fiber reinforced (SGFR) PA6,6/PP blends with 20 wt% styrene-ethylene/butylene-styrene triblock copolymers (SEBS) grafted with different levels of maleic anhydride (MA) were studied using both the essential work of fracture (EWF) and J-integral fracture toughness techniques. Good linearity was found between the plane strain specific fracture work, W_f, and the ligament length, l, in single-edge notched bend (SENB) specimens. The two fracture mechanics parameters were compared and there was good agreement between the J-integral fracture initiation toughness, J_IC, and the specific essential fracture work, W_Ie. The skin-core morphology characteristic of injection molded short fiber reinforced thermoplastics (SFRT) was also revealed using the EWF approach.     

熔体静电纺丝纤维下落过程的DPD探索模拟

静电纺丝是目前唯一能够直接、连续制备聚合物纳米纤维的方法,为了深入了解熔体静电纺丝纤维下落过程中的变化情况,探索用耗散粒子动力学介观模拟方法创建了静电纺丝模拟体系,模拟出聚合物黏度对不同阶段纤维下落速度的影响,发现纤维下落速度增加到一个最大值时,又逐渐变小;还模拟了聚合物不同链长时纺丝纤维的下落形貌,发现随着链长增加,纤维下落速度逐渐减慢;最后研究了弹簧系数对下落过程中聚合物均方末端距的影响,均方末端距增加到一个最大值时,又逐渐变小。从介观模拟的角度对熔体静电纺丝纤维下落过程进行了模拟探索,对这一物理现象中的科学问题得到了更深层次的理解。     

Dynamic mechanical analysis of novel composites from commingled polypropylene fiber and banana fiber

Polypropylene (PP)/banana fiber (BF) composites were fabricated from PP fiber and short BF by novel commingling method. The dynamic mechanical analysis (DMA) of the composites was performed with reference to BF loading and fiber surface treatments. By the incorporation of BF into the PP matrix, the storage modulus and loss modulus have been found to increase, whereas damping factor has been found to decrease. Glass transition temperature was found to increase with increase in BF loading. The viscoelastic properties of the composites were also found to depend on fiber surface treatments. The activation energy of the composites for the glass transition has been found to be increased by the increase in BF loading. Surface treatment of the BF further increased the activation energy of the composites, indicating a stronger interface for treated fiber composites. Scanning electron microscopy (SEM) photographs of the BF showed the physical changes induced by the surface treatments. Fourier transform infrared spectroscopy (FTIR) was used to ascertain the existence of the type of interfacial bonds. The use of theoretical equations to predict the storage modulus has also been discussed. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Dynamic viscoelastic behavior of styrene-grafted nylon 6 fiber

Styrene-grafted nylon 6 fibers which had been prepared by the UV irradiation method were investigated by dynamic viscoelasticity and dilatometry. It was found that nylon 6 is relaxed and polystyrene is simultaneously plasticized by nylon 6 during grafting. These phenomena are interpreted as follows. The grafting process causes nylon 6 to have a lower glass transition temperature and increases grafting frequency of polystyrene to nylon 6 by increasing the chemical junctions between the two components, so that they necessarily become more compatible.     

Cohesive fracture model for functionally graded fiber reinforced concrete

A simple, effective, and practical constitutive model for cohesive fracture of fiber reinforced concrete is proposed by differentiating the aggregate bridging zone and the fiber bridging zone. The aggregate bridging zone is related to the total fracture energy of plain concrete, while the fiber bridging zone is associated with the difference between the total fracture energy of fiber reinforced concrete and the total fracture energy of plain concrete. The cohesive fracture model is defined by experimental fracture parameters, which are obtained through three-point bending and split tensile tests. As expected, the model describes fracture behavior of plain concrete beams. In addition, it predicts the fracture behavior of either fiber reinforced concrete beams or a combination of plain and fiber reinforced concrete functionally layered in a single beam specimen. The validated model is also applied to investigate continuously, functionally graded fiber reinforced concrete composites.     

动态模拟技术与化学工程

介绍了化工过程动态模拟技术及相应软件的发展与应用状况 ,总结了动态模拟技术的最新进展。指出动态模拟技术应当与动态优化技术相结合 ,动态计算机网络管理将实现石油化工过程的连续实时优化 ,动态模拟技术将向工艺流程和生产方案的合成、能量系统集成、结合生态工业园区实例进行动态流程模拟等方向发展