Effects of raster angle on the mechanical properties of PLA and Al/PLA composite part produced by fused deposition modeling

This paper studies the mechanical properties of polylactic acid (PLA) and aluminum fiber–reinforced PLA composite (Al/PLA) specimens fabricated by fused deposition modeling (FDM) process. The effect of raster angle (0°, 90°, 45°, 0°/90°, and ± 45°) on dynamic mechanical thermal property and tensile property of FDM‐printed PLA and Al/PLA has been studied. The results show reduced tensile strength and Young's modulus in Al/PLA composite specimen in comparison with pure PLA specimen. However, the elongation‐at‐break increases, which is due to Al fiber with the higher elasticity and lower tensile strength than PLA. The addition of Al fibers improves the dynamic mechanical thermal property of pure PLA because of the good interaction of the PLA matrix with the surrounding Al fibers. Raster angle plays an important role in FDM process. All specimens printed with 0° raster angle show highest tensile strength and dynamic mechanical properties, while specimens printed with 90° raster angle have the lowest values. Fractured surfaces indicate that the failure of the specimen with 0° raster angle is due to breaking of individual layers, while for 90° raster angle, specimen fails under separation of the adjacent raster layers.     

The effect of shear on mechanical properties and orientation of HDPE/mica composites obtained via dynamic packing injection molding (DPIM)

The interfacial interaction and orientation of filler play important roles in the enhancement of mechanical performances for polymer/inorganic filler composites. Shear has been found to be a very effective way for the enhancement of interfacial interaction and orientation. In this work, we will report our recent efforts on exploring the development of microstructure of high density polyethylene (HDPE)/mica composites in the injection‐molded bars obtained by so‐called dynamic packing injection molding (DPIM), which imposed oscillatory shear on the melt during the solidification stage. The mechanical properties were evaluated by tensile testing and dynamic mechanical analysis (DMA), and the crystal morphology, orientation, and the dispersion of mica were characterized by scanning electron microscopy and two‐dimensional wide‐angle X‐ray scattering. Compared with conventional injection molding, DPIM caused an obvious increase in orientation for both HDPE and mica. More importantly, better dispersion and epitaxial crystallization of HDPE was observed on the edge of the mica in the injection‐molded bar. As a result, increased tensile strength and modulus were obtained, accompanied with a decrease of elongation at break. The obtained data were treated by Halpin–Tsai model, and it turned out that this model could be also used to predict the stiffness of oriented polymer/filler composites. Copyright © 2009 John Wiley & Sons, Ltd.     

Failure analysis of plain woven glass/epoxy laminates: Comparison of off-axis and biaxial tension loadings

An experimental study was focused on investigation of the failure properties of plain woven glass/epoxy composites under off-axis and biaxial tension loading conditions. Four fibre orientations (0°, 15°, 30° and 45° with respect to the load direction) were considered for off-axis tests and two biaxial load ratios for biaxial tests to study failure characteristics and mechanism. Four classical polynomial failure criteria - Tsai-Hill, Hoffman, Tsai-Wu and Yeh-Stratton - were analysed comparatively to predict off-axis and biaxial failure strength of the composites. For failure prediction of the plain woven composites under multiaxial tension loads, the Tsai-Wu criterion was modified by introducing an interaction coefficient F₁₂ obtained from 45° off-axis or biaxial tension tests and the Yeh-Stratton criterion was modified with the interaction coefficient B₁₂ = 0 or obtained from the biaxial tension test. The former criterion was found to have higher accuracy. Finally, according to macroscopic and microscopic studies, the failed specimens showed mostly distinct failure with a specific fracture orientation, mainly exhibiting fibre or fabric tensile fracture mode and a combination of matrix cracking and delamination, both in off-axis and cruciform samples.     

剪切作用下PA1010/PP共混物的形态与性能研究

通过动态保压注射成型方法制备了聚酰胺1010/聚丙烯(PA1010/PP)共混物,并研究了形态与性能的关系.力学性能测试结果表明在熔体冷却过程中施加剪切可以大大提高共混物的拉伸强度、拉伸模量和缺口冲击强度,当PP的质量分数为20%时,共混物的缺口冲击强度达到21.3kJ/m2,是静态样的3倍多,拉伸强度达到50.9MPa,是静态样的1.5倍.扫描电镜(SEM)结果表明在动态保压样的横断面可以观察到剪切诱导的形态,中间是芯层,围绕着芯层的是剪切层,最外面是皮层,相区尺寸显著减小、分散相分散更趋均匀,特别是PP的质量分数为20%时,相区尺寸从原来的约3.9μm降低到约1.4μm.动态保压样机械性能的提高归因于剪切作用下独特相形态的形成,分子链沿流动方向的取向是拉伸强度提高的主要原因,而剪切使分散相颗粒变小和剪切层中分子链的取向是冲击强度提高的主要原因.     

Influence of fused deposition modeling parameters on the mechanical properties of ABS parts

This work aims to determine the influence of fused deposition modeling (FDM) printing parameters on the mechanical properties of parts fabricated on an Ultimaker2 printer with acrylonitrile butadiene styrene (ABS). The effect of several parameters such as interlayer cooling time (ILCT), nozzle diameter, infill density, raster angle and layer thickness on the ultimate tensile strength, yield strength, and elastic modulus of produced parts was evaluated. Two independent studies were conducted: a first study dedicated to the ILCT and a second study where the influence of other parameters was evaluated through a design of experiments (DoE) approach. Both studies were carried out through the execution of standard tensile tests. The statistical analysis of tensile tests results was processed with the ANOVA methodology. The obtained results indicate that a reduced ILCT improves the tensile strength of parts. It is shown that nozzle diameter and infill density are the parameters that most influence the mechanical properties of ABS, with the upper range selected values improving the studied mechanical properties. The raster angle configuration of (?45^o/45^o) benefits UTS and yield strength of ABS samples. Interactions of nozzle diameter on layer thickness were detected. It was observed that smaller layer thickness promotes a higher elastic modulus and UTS; however, for thinner layers (0.06‐0.10 mm), no significant differences were found on strength of samples due to potential high distortion levels.     

Three‐dimensional printing of poly(lactic acid) bio‐based composites with sugarcane bagasse fiber: Effect of printing orientation on tensile performance

The cellulose fiber was extracted from the abandoned crop sugarcane bagasse (SCB) by means of chemical treatment methods. Poly(lactic acid) (PLA) bio‐based composites with SCB were prepared through fused deposition modeling (FDM) 3D‐printing technology, and the morphologies, mechanical properties, crystallization properties, and thermal stability of 3D‐printed composites were investigated. Compared with the neat PLA, the incorporation of SCB into PLA reduces the tensile strength and flexural strength of 3D‐printed samples but increases the flexural modulus. The difference in tensile performance and bending performance is that the tensile strength of 3D‐printed samples is best when the SCB content is 6 wt%, while the flexural modulus continuously decreases as the SCB content increases. Furthermore, the effects of various printing methods on the tensile performance of 3D‐printed samples were explored via modifying G‐code of 3D models. The results indicate that the optimum SCB fiber content is identical for all printing methods except method “vertical.” Due to the fibers and molecular chains are oriented to varying degrees with altering raster angle in 3D‐printed samples, the fully oriented sample printed by method “parallel” has a better tensile strength. Besides, SCB exhibits enough high thermal decomposition temperature to meet requirements for melt extrusion processing of PLA composites, and SCB fiber is capable of promoting the crystallization of PLA.     

Fused Deposition Modelling of high temperature polymers: Exploring CNT PEEK composites

The Fused Deposition Modelling (FDM™) process owes its popularity to its hardware versatility, low cost and wide range of materials (and colours) available. In this study, PEEK was produced with 1% and 5% carbon nanotubes (CNTs) and processed in a modified FDM system able to operate with high temperature polymers. The tensile strength, layer bonding and microstructure of the plain and CNT loaded PEEK samples were investigated throughout the three steps of manufacturing: compounded composite feedstock filaments, single FDM deposited layers and fabricated test specimens. Interestingly, every step of processing seems to fabricate structures of lower performance. As part of the characterisation of the FDM structures, short shear beam tests were used as a new method to assess layer-to-layer bonding.     

Morphology and mechanical behavior of isotactic polypropylene with different stereo‐defect distribution in injection molding

Large amount of work has been published on the isotacticity–properties relationship of isotactic polypropylene (iPP). However, the stereo‐defect distribution dependence of morphology and mechanical properties of iPP injection molding samples is still not clear. In this study, two different isotactic polypropylene (iPP) resins (PP‐A and PP‐B) with similar average isotacticity but different stereo‐defect distribution were selected to investigate the morphology evolution and mechanical properties (tensile and notching) of their injection molding samples using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), 2D wide angle X‐ray diffraction (2D‐WAXD), and scanning electron microscope (SEM). The results of DMA showed that the molecular movement ability of PP‐A (with less uniform distribution of stereo‐defect) was stronger than that of PP‐B, meanwhile the analysis of DSC and SEM suggested that after injection molding, smaller spherullites, and crystals with higher perfection had formed in the specimens of PP‐A. The resulting of tensile properties of PP‐A were found to be better than that of PP‐B. The results of morphology evolution by SEM observation and 2D‐WAXD showed that PP‐A is more likely to occur interspherulite deformation and can disperse the tensile stress more efficiently, and therefore, its crystal structure can withstand a greater force when tensile stress is applied. On the other hand, PP‐B has larger spherulites and boundaries, and low perfection of lamellaes, and the intraspherulte deformation tend to take place. It is easier for the crystal of PP‐B to be broken up and reoriented along the tensile direction. Copyright © 2014 John Wiley & Sons, Ltd.     

Weibull statistical analysis and experimental investigation of size effects on tensile behavior of dry unidirectional carbon fiber sheets

In this study, experimental tests and a statistical analysis are conducted to verify the size effects associated with length on the tensile behavior of dry unidirectional carbon fiber sheets (DUCFS). As a statistical method, the two-parameters Weibull theory is considered. To verify the validity of the Weibull theory, four sets of direct tensile test were made on DUCFS specimens having different lengths. The direct tensile tests consist to evaluate the size effects associated with length on the mechanical properties of DUCFS such as tensile strength and the Young's modulus. The experimental results show a size effect of length on the tensile strength of DUCFS. Indeed, the tensile strength decreases when increasing the specimen length. In addition, the experimental results demonstrate that there is no size effect on the failure mode and on the Young's modulus of DUCFS. Finally, Weibull weakest link theory is used to predict the tensile strength size effect on DUCFS specimens. A good agreement was shown between the test data and predicted results obtained using the Weibull weakest link theory.     

Properties of glass-fiber reinforced composites based on liquid diglycidyl ether of bisphenol-c-epoxy resin

Glass-fiber reinforced epoxy composites were fabricated from the matrix resin liquid diglycidyl ether of bisphenol-C (DGEBC) using various amines as curing agents with and without fortifier (20 phr). The epoxy laminates were evaluated for their mechanical properties, such as flexural strength, interlaminar shear strength (ILSS), tensile strength and shore-D hardness. Dielectric properties, such as the dielectric constant, tan δ, dielectric loss and the resistivity of the laminated samples, were measured. The effect of the chemical reagents on the mechanical properties (i.e. flexural strength, lLSS) was also studied.     

Drop-weight impact tests and finite element modeling of cast acrylic/aluminum plates

As an extension of a previous study [1], drop-weight impact tests on cast acrylic (PMMA) plates reinforced by aluminum face sheets were carried out using an instrumented drop weight impact tester. The PMMA and aluminum layers were adhered by epoxy cured at room temperature. Depending on the impact velocity and the type of top surface (acrylic or aluminum) struck by the impactor, damage caused by impact included partial or full delamination at the interface and radial cracks in the acrylic layer. The higher the impact velocity, the more damage was induced. More severe damage occurred if the bi-layer plate was impacted on the aluminum side. The ultrasonic C-scan technique was adopted to detect the damage. The pulse-echo technique with a focused transducer provided very good C-scan results for detecting damage patterns. The transducer with higher frequency gave better resolution and showed more details of damage. Finally, the finite element program, LS-DYNA, implemented with maximum strength criterion for radial cracking and mixed mode strength criterion for interfacial fracture, was used to simulate the drop weight impact tests. Impact force history, energy partition and delamination were predicted assuming various boundary conditions according to experimental results. The finite element simulations were in very good agreement with the experimental data.     

Effects of fused deposition modeling process parameters on tensile,dynamic mechanical properties of 3D printed polylactic acid materials

Fused deposition modeling (FDM) is an important process among the available additive manufacturing technologies in various industries. Although there exists many works investigating the effects of FDM process parameters on the mechanical properties of printed materials, there are still several points need to be studied. One is the effects of process parameters on the dynamic mechanical properties of FDM-printed materials, especially in environments where the temperature often changes. The other is the mechanism by which process parameters affect the mechanical properties of printed materials. Aiming at these two points, uniaxial tensile tests and dynamic mechanical analysis are carried out respectively to characterize the tensile properties and dynamic mechanical properties of FDM-printed PLA materials under different FDM process parameters, namely printing angle, layer thickness, fill rate and nozzle temperature. Based on the experimental results explanations are given for the influence of the FDM process parameters on the mechanical properties of the printed materials.     

Effects of stereo-defect distribution on the crystalline morphology and tensile behavior of isotactic polypropylene prepared by compression molding process

In this study, the aggregation morphology, tensile behavior, and morphology evolution during the tensile test of two isotactic polypropylene (iPP) samples with similar molecular weight and average isotacticity but different uniformities of stereo-defect distribution are investigated by differential scanning calorimetry (DSC), two-dimensional wide angle X-ray diffraction (2D-WAXD), and scanning electronic microscopy (SEM). The results revealed that the uniformity of stereo-defect distribution of iPP determines the crystalline structure and aggregation morphology, and further influences the tensile behavior and morphology evolution during the tensile test. For PP-A with less uniform stereo-defect distribution, its ability of crystallization is stronger compared with PP-B, resulting in smaller spherulite sizes, higher melting point and degree of crystallinity, and narrower distribution of lamellar thickness of the compression molding specimens. During the tensile test, mainly the inter-spherulite deformation takes place at the early stage for deformation, which further results in drastic deformation of lamellar and high degree of reorientation at the strain increases, exhibiting higher yield strength and elastic modulus, and lower elongation at break compared with PP-B; for PP-B with more uniform stereo-defect distribution, larger spherulite sizes, lower melting point and degree of crystallinity in its compression molding sample are observed. During the tensile test, intra-spherulite deformation mainly takes place, which can disperse the tensile stress more uniformly. As the strain increases, lower degree of crystalline destruction and reorientation of the crystallites take place. The yield strength and elastic modulus of PP-B is lower than PP-A, and its elongation at break is higher.     

Physical and mechanical properties of graphene oxide/polyethersulfone nanocomposites

The aim of this study was to investigate physical and mechanical properties of graphene oxide (GO)/polyethersulfone (PES) nanocomposite films. The films were produced by solution casting method. The mechanical properties of composite films were evaluated by tensile test. A significant enhancement in the mechanical properties of neat PES films was obtained incorporating a small amount of GO loading (0.05–1 wt.%). The highest tensile strength was observed at 1 wt.% of GO. Comparisons were made between experimental data and the Halpin–Tsai model predictions for the tensile strength and modulus of GO/PES composites. The effect of an orientation factor on model predictions was also acquired. The hydrophilicity of the nanocomposite was evaluated by assessing contact angle and enhanced wet ability of the films was obtained with increasing the amount of GO up to 1%. The morphology of the nanocomposites was investigated using scanning electron microscopy and transmission electron microscopy and the results revealed a good dispersion of GO in the PES matrix. The thermal behavior of the composite was also studied. Thermal stability of composites was increased by adding the GO. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of laser scanning speed on surface roughness and mechanical properties of aluminum/Polylactic Acid (Al/PLA) composites parts fabricated by fused deposition modeling

Although fused deposition modeling (FDM) has gradually become one of the popular additive manufacturing technologies in different industries, high surface roughness has always been an inevitable disadvantage of FDM parts. Laser polishing represents a recent and novel application of laser surface irradiation that can be used for precise, post-process smoothing of the rough surfaces commonly encountered on FDM parts. The influence of laser polishing on surface modification and mechanical properties of aluminum/Polylactic Acid (Al/PLA) composites has been investigated. Laser scanning speed was varied to evaluate its effect on the surface quality and mechanical properties of the experimental samples. The results indicated that laser polishing could enable reductions in surface roughness of over 86.6% (from 23.27 μm to 3.11 μm Sa). The tensile strength of specimen also increased from 41.01 MPa to 51.31 MPa with increasement of 25.1%. The dynamic mechanical analysis (DMA) results showed that there was a remarkable improvement in the storage modulus and glass transition temperature of Al/PLA composite specimens after laser polishing, which suggested that the laser polishing treatment could play a role in decreasing the porosity inside the FDM parts and improve interfacial adhesion between the PLA matrix and Al fibers. Moreover, the fracture morphologies were observed to investigate the possible strengthening mechanism. These results demonstrate how laser polishing can simultaneously smooth and modify the surface characteristics of a FDM part surface.     

在低频振动场中注射成型HDPE试样的力学性能及其形态控制

利用自行研制的低频振动注射实验装置探讨HDPE振动注射试样力学性能和微观形态之间的关系 .实验中对常规注射和振动注射成型的试样力学性能和微观形态进行了对比实验 .SEM实验结果显示 ,振动注射制件芯层的形态由常规注射的球晶转变为垂直于振动波传递方向排列的片晶结构 ,在剪切层中同时存在串晶或柱状堆砌的片晶结构 .频率的改变 (0 相似文献   

Residual stresses and birefringence in injection molding of amorphous polymers: Simulation and comparison with experiment

A physical modeling and a two‐dimensional numerical simulation of the injection‐molding of a disk cavity by using a hybrid finite element method (FEM) and finite difference method (FDM) are presented. Three stages of the injection‐molding cycle––filling, packing, and cooling––are included. The total residual stresses are taken to be a sum of the flow stresses calculated using a compressible nonlinear viscoelastic constitutive equation and the thermal stresses calculated using a linear viscoelastic constitutive equation. The total residual birefringence is taken to be the sum of the flow birefringence related to the flow stresses through the stress–optical rule, and the thermal birefringence related to the thermal stresses through the photoviscoelastic constitutive equation. The Tait equation is used to describe the P‐V‐T relationship. The simulation shows that without packing the birefringence in the surface layer of moldings, with its maximum near the surface, is caused by the frozen‐in flow birefringence (flow stresses) and in the core region by the frozen‐in thermal birefringence (thermal stresses). With packing, a second birefringence maximum appears between the center and the position of the first maximum due to flow in the packing stage. The predicted birefringence profiles and extinction angle profiles are found to be in fair agreement with corresponding measurements in literature for disk moldings. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 622–639, 2006     

Fabrication and properties of poly(propylene carbonate)/calcium carbonate composites

Composites of poly(propylene carbonate) (PPC) reinforced with micrometric and nanometric calcium carbonate particles were prepared via melt mixing followed by compression molding. The morphology and mechanical and thermal behaviors of the composites were investigated. Static tensile tests showed that the tensile strength, stiffness, and ductility of the composites tended to increase with increasing contents of micrometric calcium carbonate particles. This improvement in the tensile properties was attributed to good interfacial adhesion between the fillers and matrix, as evidenced by scanning electron microscopy examination. However, because of the agglomeration of calcium carbonate nanoparticles during blending, those composites with nanoparticles exhibited the lowest tensile strength. Thermogravimetric measurements revealed that the incorporation of calcium carbonate into PPC resulted in a slight improvement in its thermooxidative stability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1806–1813, 2003     

Ibuprofen-loaded PCL meshes manufactured using rapid tooling for ocular orbital repair

This study investigated the manufacture of resorbable polycaprolactone/ibuprofen (PCL/IBP) meshes by injection molding for application in ocular orbital repair. The pore dimension sizes used demonstrate that micro-porous meshes can be manufactured by injection molding using a prototype mold. The mechanical properties were observed to be dependent on the material composition and morphology. Lower stiffness, strength and elongation at failure were observed for the 8 mm pore sized samples. The PCL/Ibuprofen meshes initially showed a fast drug release but after 3 days the release was slow and controlled. The cytotoxicity test results of the PCL/Ibuprofen meshes indicated that the large initial quantity of Ibuprofen released was too high and resulted in cell toxicity. However, after this initial release, the PCL/Ibuprofen meshes showed a good interaction with the cells seeded on their surface. The presence of a low concentration of Ibuprofen does not negatively influence cell viability in culture.     

Specimen design for mechanical testing of highly-oriented polymers

Tensile and in-plane shear specimens have been designed using finite element analysis to enable satisfactory testing of highly-drawn flat strip polymer. The analyses have shown that the required specimen geometry for tensile testing is very dependent on the degree of anisotropy of the material. A geometry correction factor has been determined for the in-plane shear specimen to relate the applied load to the shear stress at the centre of the gauge area. Simple tube specimens have also been analysed using anisotropic thin shell theory.