Mechanical properties of components fabricated with open-source 3-D printers under realistic environmental conditions

The recent development of the RepRap, an open-source self-replicating rapid prototyper, has made 3-D polymer-based printers readily available to the public at low costs ( < $500). The resultant uptake of 3-D printing technology enables for the first time mass-scale distributed digital manufacturing. RepRap variants currently fabricate objects primarily from acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA), which have melting temperatures low enough to use in melt extrusion outside of a dedicated facility, while high enough for prints to retain their shape at average use temperatures. In order for RepRap printed parts to be useful for engineering applications the mechanical properties of printed parts must be known. This study quantifies the basic tensile strength and elastic modulus of printed components using realistic environmental conditions for standard users of a selection of open-source 3-D printers. The results find average tensile strengths of 28.5 MPa for ABS and 56.6 MPa for PLA with average elastic moduli of 1807 MPa for ABS and 3368 MPa for PLA. It is clear from these results that parts printed from tuned, low-cost, open-source RepRap 3-D printers can be considered as mechanically functional in tensile applications as those from commercial vendors.     

Influential factors in determining the adhesive strength of ACF joints

This paper analyzes the 90° peel strength of model ACF (anisotropic conductive films) joints between flex and glass substrates, evaluated under various test speed s. The model ACF joints were bonded under a variety of conditions in order to achieve a range of curing states of the adhesive binder in the ACF. The peel strength of the joints is strongly influenced by anchoring effects caused by both the dimple structure and the circuit pattern on the polyimide film of the flex. In order to induce an acceptable anchoring effect, the adhesive binder of the ACF needs to be cured adequately in order to exhibit sufficient mechanical strength. Although the peel strength of the joints tends to increase with increasing conversion degree of the binder, it does not increase smoothly during the curing process. The peel strength increases drastically at a particular conversion degree, which is related to the formation of a cross-linked polymer structure. The peel strength of the joints exhibits a significant dependence on test speed, due to the viscoelasticity of the binder. Although the peel strength is almost intrinsically saturated when the drastic increase originating from the formation of the cross-linked structure occurs, the extent of the test speed dependency differs depending on the curing conditions. Furthermore, interfacial factors (such as chemical interactions) are suggested as having an influence on the peel strength of the joints in some cases.     

On the mechanical behavior of BFRP to aluminum AA6086 mixed joints

The aim of this work is to analyze the possibility to join aluminum alloy AA6086 and composite laminates reinforced with basalt fibers, an innovative material which use is growing in several applications as an alternative to glass fibers. To this goal, three joining techniques were investigated: mechanical by Self Piercing Riveting (in the next called SPR), adhesive by co-curing technique and mixed in which the joining techniques (i.e. adhesive and mechanical) were combined. Two manufacturing technologies (i.e. hand lay-up and vacuum bagging) were used both to produce composite substrates and to realize co-curing adhesion between the substrates to be joined. Mixed joints were realized by inserting the rivets in co-cured joints after 48 h than the initial phase of the curing process (i.e. the phase of mixing the resin with own hardener). Overall, six lots of joints were realized (two for each joining technique). All joints were characterized by performing single lap joint tests. The mechanical results were analyzed through a two way analysis of variance.The experimental results show that adhesive joints, realized by vacuum bagging method, show average failure load 22.9% higher and standard deviation 70.6% lower than those realized by hand lay-up, respectively. This means that the vacuum bagging technology allows to increase the adhesion strength of the interface between metal sheet and Basalt Fiber Reinforced Polymer (in the next BFRP), allowing the above failure load growth. Furthermore the failure mechanisms change from adhesive mode to partially cohesive one for the adhesive joints realized by hand lay-up and vacuum bagging, respectively. By comparing mixed joints, different results are obtained: i.e. the hand lay-up joints show both higher average failure load (+42.9%) and standard deviation (+208.3%) than those realized by vacuum bagging. The poor performances of the mixed joints realized by vacuum bagging can be considered due to the excessive value of the chosen riveting load. Statistically, two variables were investigated: i.e. joining technology (i.e. mechanical, adhesive and mixed) and manufacturing process (i.e. hand lay-up and vacuum bagging). These can influence the properties of the joints. In particular, the joining technology results a significant factor. Moreover, an interaction between the two variables exists.     

碳纤维增强聚乳酸复合材料体外降解特性

制备了碳纤维增强聚乳酸(C/ PLA) 骨折内固定复合材料, 研究了体外降解过程中其力学性能的变化。结果表明: 在体外降解过程中, C/ PLA 复合材料的各项力学性能均有不同程度的下降, 但经过硝酸处理后的C/PLA 复合材料降解速度缓慢, 表明界面结合强度的提高对降解过程起抑制作用。      

基于图像处理的碳纤维增强树脂基复合材料固化压力-缺陷-力学性能建模与评估

利用热压罐成型工艺制备了不同固化压力条件下的碳纤维增强树脂基复合材料层合板,分析了超声相控阵C扫描图像与微观缺陷的对应关系,研究了固化压力、孔隙缺陷及力学性能之间的关联规律。结果表明：利用超声C扫描图像差异能够表征孔隙等缺陷含量,在本实验条件下,固化压力由0 MPa提高到0.6 MPa,复合材料孔隙率降低96.7%,拉伸强度（TS）和层间剪切强度（ILSS）分别提高56.1%和68.8%。在此基础上,对不同固化压力条件下制备的复合材料层合板的超声相控阵C扫描图像进行图像处理并定义成型质量指数,实现了基于C扫描图像对孔隙缺陷的定量表征。最后,通过对孔隙缺陷检测、力学性能测试及图像定量化评价结果进行数学拟合,建立了基于图像处理的固化压力-缺陷-力学性能之间的数学关联模型（CPDMP模型）,并给出了成型质量指数阈值为81%,及可接受的孔隙率应不高于1.1%,相应的固化压力应不低于0.35 MPa。     

Fatigue properties of combined friction stir and adhesively bonded AA6082‐T6 overlap joints

Even though friction stir welding (FSW) has been shown to produce high performing butt joints, stress concentration at the weld edges in overlap FSW significantly reduces the performance of these joints. By combining FSW and adhesive bonding into a friction stir (FS) weld bonding, joint mechanical performance is greatly improved. Quasistatic and fatigue strength of the proposed FS weld‐bonding joints was assessed and benchmarked against overlap FSW and adhesive bonding. The characterization of the structural adhesive is also presented, including differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), as well as mechanical characterization with curing temperature. A small process parameter study was made to select proper FSW parameters for AA6082‐T6 overlap FSW and FS weld‐bonded joints. FS weld bonding achieved a significant increase in quasistatic and fatigue strength when compared with overlap FSW, with 79.9% of the fatigue strength of adhesive‐bonded joints at 10⁶ cycles, whereas FSW had 41.6%.     

Improvement on the properties of polylactic acid (PLA) using bamboo charcoal particles

Bamboo charcoal (BC) derived from bamboo plants is one kind of well recognized multi-functional materials which has been used in various applications such as medical, cosmetic, food processing and health-related products. In this paper, BC particle is used as reinforcement for polylactic acid (PLA) to enhance its mechanical, thermal and optical properties. The comparison on tensile, flexural and impact properties of BC particle reinforced PLA composites (BC/PLA composites) with the content ranging from 2.5 to 10 wt.% is conducted. Experimental results indicated that the maximum tensile strength, flexural strength and ductility index (DI) of BC/PLA composites increased by 43%, 99% and 52%, respectively as compared with those of neat PLA. This phenomenon was attributed to the uniform distribution of high aspect ratio and surface area of BC particles. Further increasing the BC content to 7.5 wt.% would decrease the glass transition temperature of BC/PLA composites. The mechanical properties of BC/PLA composites were reduced as compared with a neat PLA sample when they were exposed to compost degradation. However, less reduction in these properties was found when they were subject to UV irradiation. UV–Vis spectrometer analysis supported the results of UV irradiation. Fracture surfaces of tensile test samples with and without compost degradation or UV irradiation were analysed by using scanning electron microscopy (SEM). SEM images revealed that there was a good BC particle dispersion in the composites through extrusion and injection moulding processes if the particle content was below 7.5 wt.%.     

Investigation on the mechanical strength of magnetic hollow silica prepared from Pickering emulsion route

In this paper, a one-pot sol–gel method was used to synthesize magnetic hollow silica through Pickering emulsion route. The mechanical strength of as-prepared magnetic hollow silica was adjusted and investigated. It was found that the emulsion droplet in Pickering emulsion was solely stabilized by cetrltrimethylammionium bromide (CTAB)-modified Fe₃O₄ particles while the silica source originally dispersed in oil phase was hydrolyzed at the emulsion droplet interface. This led to the formation of silica that then coated on the interface of the emulsion droplet to create magnetic hollow silica after being washed and dried. Controlling the hydrolyzing rate and degree of silica source and enhancing the binding force between silica and Fe₃O₄ nano particles can improve the mechanical strength of magnetic hollow silica.     

Effect of extrusion drawing and twist-orientation on mechanical properties of self-reinforced poly(lactic acid) screws

In order to improve torsional strength of a bioabsorbable poly(lactic acid) (PLA) screw, twist-orientation method was developed in this study. PLA screws were prepared through a series of routes including compression molding, extrusion method, twist-orientation, and forging. Shear and torsional strength were measured as mechanical properties of screw. As a result, twist-orientation improves torsional strength of PLA screw without the decrease in shear strength. The maximum torsional strength was obtained at helix angle of 45° and extrusion ratio of 8. This is because fibrous crystals were oriented close to the direction of principal tensile stress which occurred during torsion test. Since this principal stress occurs in the 45° direction on the surface of specimen, the maximum torsional strength is achieved by twist-orientation at this helix angle.     

The effect of stirring rate on semisolid stirring brazing of SiCp/A356 composites in air

This paper explores the possibilities of joining SiC_p/A356 composites using semisolid Zn27Al filler metal with aid of mechanical stirring. Moreover, the effect of stirring rate on the macro-appearance, microstructure, bonded ratio, braze metal ratio of joints and the tensile strength of joints were investigated. Experimental results show that the bonded ratio of interface, braze metal ratio and the tensile strength of the joints is rise with increasing of stirring rate. It is indicated that increasing of stirring rate will promote the disruption of oxide film on surface of composites so as to enhance metallurgical bonds at joint interface. In addition, increasing of stirring rate will also promote formation to fine brittle η-Zn phase and its uniform distribution in bond.     

Influence of post-curing and coupling agents on polyurethane based copper filled electrically conductive adhesives

Effects of post curing and silane coupling agents with different functional groups such as epoxy, isocyanate and ureide on the electrical and mechanical properties of copper (Cu) filled electrically conductive adhesives (ECAs) were studied. Micron-sized Cu particles were used as conductive fillers and polyurethane resin was applied as the adhesive material. Significant differences could be observed on the as cured electrical resistivity and shear strength of the Cu filled ECAs joints prepared with different silane coupling agents. Silane coupling agents functionalized with epoxy groups yielded the lowest electrical resistivity and highest shear strength among the ECAs in this study. Besides, effect of post-curing at 170 °C for 1 h on the ECAs was also investigated. Results showed that ECAs after post-curing exhibited enhanced electrical conductivity and shear strength compared to the as cured ECAs.     

Metallurgical and mechanical characterization of electron beam welded DP600 steel joints

Several new commercial advanced high-strength steels exhibit high strength and enhanced formability. These materials have the potential to affect cost and weight saving while improving performance. However, welding, by modifying the microstructure of the steel, has in general a detrimental effect on the mechanical properties of structural components. If high power density technologies are used, the result is that the mechanical properties of such kind of joints can be improved. This article presents a metallurgical and mechanical characterization of electron beam welded joints in advanced high-strength steel DP600. The experimental analysis was supported by a thermal numerical model obtained through the Sysweld^? code. Results show that mechanical properties of the electron beam welded joints are comparable with those of parent metal both in terms of static strength and ductility.     

C/PLA复合材料的体外降解特性研究

对C／PLA复合材料的体外降解特性进行了研究。考察了该复合材料在降解过程中吸水率,质量损失和宏观力学性能的变化,并与PLA进行了对比。结果表明,与PLA相比,C／PLA复合材料的吸水率增加,质量损失下降,弯曲强度和剪切强度的下降速度减小。在体外降解过程中,C／PLA复合材料的界面发生降解,界面弱化是造成复合材料力学性能下降的主要因素。     

Ductile PLA nanocomposites with improved thermal stability

Polylactide (PLA) is used as a biomedical material because it is biodegradable, but the vast majority of biodegradable polymers in clinical use are composed of rather stiff materials that are unsuitable for use in numerous applications because they exhibit limited extendibility, weak mechanical strength, and poor thermal stability. We modified PLA with 2-methacryloyloxyethyl isocyanate (MOI) to prepare ductile PLA materials. By utilizing a novel sol–gel process, PLA nanocomposites were further prepared with improved mechanical properties and thermal stability. The 10% thermal decomposition temperature for PLA modified with 5% MOI and 5–10% silica was 21–32 °C higher than that of original pristine PLA. Elongation at break increased by 4–13 times when compared to neat PLA while the tensile strength was maintained at 30–40 MPa. These synthesized PLA nanocomposites can be applied as biomaterials with improved mechanical and thermal properties.     

苯乙烯-丙烯酸甲酯共聚物对聚苯乙烯/聚乳酸共混物力学性能和流变性能的影响

采用无皂乳液聚合法合成了苯乙烯-丙烯酸甲酯共聚物(PSMA)(n(St)∶n(MA)=75∶25),将PSMA与聚苯乙烯(PS)和聚乳酸(PLA)熔融共混制备了PSMA含量不同的PS/PLA共混物(m(PS)∶m(PLA)=1∶4),利用扫描电子显微镜、电子拉力机和转矩流变仪对共混物的相结构、力学性能以及流变行为进行了表征。结果表明,加入少量PSMA即能有效提高PLA与PS的相容性,减小PS/PLA共混物中分散相的相尺寸,提高PLA与PS两相间粘接作用;加入质量分数为0.5%的PSMA时,PS/PLA共混物的力学性能达到最佳;未加PSMA时,PS/PLA共混物在高剪切速率下剪切变稀显著,甚至低于纯PS,加入PSMA后,在高剪切速率下的剪切变稀程度与纯PLA相当。     

Relationship between the morphology of PMMA particles and properties of acrylic bone cements

Bone cements are mainly based on acrylie polymers, poly (methyl methacrylate) (PMMA) being the most representative. The curing process (cold curing) is the result of the free radical polymerization of a mixture of beads of PMMA and methyl methacrylate (MMA), initiated by benzoyl peroxide (BPO) and activated by the presence of a tertiary amine, the most classical being N,N-dimethyl-4-toluidine (DMT). In this work the results on the effect of the size and size distribution of PMMA beads and the concentration of DMT and BPO on the setting parameters, the residual monomer content and the mechanical properties (tension and compression) of the cured systems are presented. The use of relatively larger diameter PMMA beads improves the characteristic parameters of the curing process (decreasing the peak temperature and increasing the setting time), without detrimental effects on the mechanical properties of the cured cement.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporio, Portugal, 10–13 September.     

Effects of compound curing agent on the thermo-mechanical properties and structure of epoxy asphalt

Epoxy asphalt curing system was prepared by sebacic acid compound with methyl-tetrahydrophthalic anhydride (MeTHPA) or Tung oil anhydride (TOA). Tensile strength, penetration, differential scanning calorimetry, dynamic mechanical thermal analysis, torn section microscopy photographs and scanning electron microscope analysis were utilised to investigate the mechanical properties, thermodynamic behaviour and micro-structure of epoxy asphalt curing systems under different curing agents. The results showed that in the presence of compound curing agent, the tensile strength and surface hardness of the epoxy asphalt curing system effectively improved, the induction period of the curing reaction decreased, the curing reaction mechanism turned to one-step reaction from two-step reaction, the Tg of asphalt phase and epoxy phase could simultaneously increase, and high-temperature damping performance also improved, but the particle size of asphalt dispersed in epoxy resin becomes uneven, while the curing system becomes semi-brittle from toughness. Compared to TOA, the effects of MeTHPA on such performance were more obvious.     

聚乳酸/热塑性淀粉/POE-g-GMA共混材料的制备和性能

采用甲基丙烯酸缩水甘油酯（GMA）接枝（乙烯/辛烯）共聚物（GPOE）作为增韧剂,利用Haake转矩流变仪熔融制备了聚乳酸（PLA）/热塑性淀粉（TPS）/GPOE共混材料。通过拉伸、冲击、动态热力学、差示扫描量热、扫描电镜等方法对共混材料进行研究：PLA共混材料伸长率可达到400%左右,冲击性能有大幅提高;TPS中甘...     

纳米二氧化钛含量对秸秆/聚乳酸复合材料性能的影响

目的 为改善纤维增强聚乳酸(PLA)复合材料增强相与基体相之间差的界面结合。方法 以秸秆粉(SP)为填料,纳米二氧化钛(TiO2)作为界面改性剂,构建SP/PLA复合材料相容界面,通过力学性能测试、吸水率测试、扫描电子显微镜(SEM)、X射线衍射(XRD)和热重分析法(TGA)等表征手段,探究不同含量纳米二氧化钛对SP/PLA复合材料力学性能和界面相容性的影响。结果 研究发现,纳米二氧化钛的质量分数为2.0%时,复合材料的拉伸强度和弯曲强度分别达到42.78 MPa和91.25 MPa,其耐水性能、结晶度、耐热性能也达到最好。结论 纳米二氧化钛可有效提高秸秆/聚乳酸复合材料的性能。     

Improve the Strength of PLA/HA Composite Through the Use of Surface Initiated Polymerization and Phosphonic Acid Coupling Agent

Bioresorbable composite made from degradable polymers, e.g., polylactide (PLA), and bioactive calcium phosphates, e.g., hydroxyapatite (HA), are clinically desirable for bone fixation, repair and tissue engineering because they do not need to be removed by surgery after the bone heals. However, preparation of PLA/HA composite from non-modified HA usually results in mechanical strength reductions due to a weak interface between PLA and HA. In this study, a calcium-phosphate/phosphonate hybrid shell was developed to introduce a greater amount of reactive hydroxyl groups onto the HA particles. Then, PLA was successfully grafted on HA by surface-initiated polymerization through the non-ionic surface hydroxyl groups. Thermogravimetric analysis indiated that the amount of grafted PLA on HA can be up to 7 %, which is about 50 % greater than that from the literature. PLA grafted HA shows significantly different pH dependent ζ-potential and particle size profiles from those of uncoated HA. By combining the phosphonic acid coupling agent and surface initiated polymerization, PLA could directly link to HA through covalent bond so that the interfacial interaction in the PLA/HA composite can be significantly improved. The diametral tensile strength of PLA/HA composite prepared from PLA-grafted HA was found to be over twice that of the composite prepared from the non-modified HA. Moreover, the tensile strength of the improved composite was 23 % higher than that of PLA alone. By varying additional variables, this approach has the potential to produce bioresorbable composites with improved mechanical properties that are in the range of natural bones, and can have wide applications for bone fixation and repair in load-bearing areas.