Tensile strength and fracture of glass fiber-reinforced plastic (GFRP) plate with an eccentrically located circular hole

In this paper, tensile strength and fracture of finite glass fiber-reinforced plastic GFRP (glass/polyester) composite materials with a through-the-thickness eccentrically located circular hole are experimentally studied. The strain response histories near the hole boundary for different eccentrically located holes during the whole damage and fracture process of the notched specimen are recorded. The effects of off-center distance and hole diameter on strength and fracture of the notched specimen are analyzed. The tensile fracture strength of the notched specimen with an eccentrically located hole is determined. Also, the initial stress concentrations in the composite laminate due to the presence of the eccentrically located hole are understood. These results play an important role for predicting strength and evaluating lifetime of laminate composite with complex geometrical cutouts.     

兼具导热和自修复功能的聚合物复合材料

针对聚合物复合材料存在的结构受损导致导热和力学强度降低的问题,提出利用导热填料增强自修复聚合物,实现导热性能和力学强度的快速修复.通过对双(3-氨丙基)封端的聚二甲基硅氧烷(H2N-PDMS-NH2)进行端基改性,得到脲基嘧啶酮(UPy)双封端的聚二甲基硅氧烷(UPy-PDMS-UPy),于60°C下20 h后拉伸强度修复效率可达86.6%.进一步填充羟基化氮化硼(mBN)制备兼具自修复功能的导热复合材料,研究发现mBN的填充导致复合材料强度提高但韧性降低,对导热性能和自修复功能分别起积极和不利影响.当mBN含量为30 wt%时,热导率高达2.579 W·m-1·K-1,于60°C下40 h后拉伸强度修复效率达82.0%.红外热像仪显示,损伤处接触10 h后,m BN-30/UPy-PDMS-UPy上表面温度接近初始温度,展现出导热通路的修复特征,实现导热与自修复功能的兼备.     

Thermal and mechanical properties of cassava and pineapple flours-filled PLA bio-composites

The research focused on enhancing the mechanical properties and thermal stability of bio-composites with natural flours and improving the interfacial adhesion between biodegradable polymer and flour. The tensile and flexural strength of the PLA bio-composites decreased with increasing flour addition. However, a 3% loading of the compatibilizer in the PLA bio-composite increased this strength up to that observed with the 10% loading flour. The degradation temperature of PLA was decreased by the flour but destarched cassava flour had higher thermal stability on account of its higher lignin content than pineapple flour. This means that the PLA bio-composites with destarched cassava flour had higher thermal stability than those with the pineapple flour. In addition, the thermal degradation temperature was increased by adding MAPLA. The compatibilizer improved the crystallinity of PLA, which enhanced the mechanical strength of the PLA bio-composites. As the pineapple flour and destarched cassava flour 30% loading was increased, the HDT of the PLA bio-composites increased from 56.8?°C to ~66.3 and 69.7?°C, respectively. The thermal aging test showed no reduction in strength of the neat PLA. However, the PLA bio-composites showed a gradual decrease in tensile strength with increasing number of cycles. Moreover, the shrinkage ratio of the neat PLA was 5% of that found with the PLA resin.     

Influence of multiple processing on selected properties of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)

The effect of multiple (up to 10 times) injection molding of processed poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P(3,4HB)) on its phase transition temperatures, degree of crystallinity, degradation temperature, mass flow rate, mechanical properties, dynamic mechanical properties, and Charpy's impact strength is presented. The studies have shown that the multiple injection lowers the degree of crystallinity and the thermal stability of P(3,4HB). The mass flow rate values increased with increasing the injection number. It was found that the multiple injections had no substantial effect on the tensile strength up to 10 injection cycles and the tensile strength at break, tensile strain at tensile strength, and tensile strain at break up to 6 injection cycles. The maximum value of storage modulus at 30 °C and impact strength were recorded for sample after 4 cycles of injection, while the values of storage modulus at 120 °C increased with increase of the injection cycles. Copyright © 2015 John Wiley & Sons, Ltd.     

Additive manufacturing of continuous carbon fiber reinforced poly-ether-ether-ketone with ultrahigh mechanical properties

Continuous carbon fiber reinforced poly-ether-ether-ketone (CCF/PEEK) composites have attracted significant interests in mission-critical applications for their exceptional mechanical properties and high thermal resistance. In this study, we additively manufactured CCF/PEEK laminates by the Laser-assisted Laminated Object Manufacturing technique, which was recently reported by the authors. The effects of laser power and consolidation speed on the flexural strength of the CCF/PEEK composites were studied to obtain the optimal process parameters. Hot press postprocessing was performed to further improve the mechanical properties of the composites. Various fiber alignment laminates were prepared, and the flexural and tensile properties were characterized. The hot press postprocessing 3D printed unidirectional CCF/PEEK composites exhibited ultrahigh flexural modulus and strength of 125.7 GPa and 1901.1 MPa, respectively. In addition, the tensile modulus and strength of the composites reached 133.1 GPa and 1513.8 MPa. The results showed that the fabricated CCF/PEEK exhibited superior mechanical performance compare to fused filament fabrication (FFF) printed carbon fiber reinforced thermoplastics (CFRTP).     

Mechanical,Thermal and Morphological Behaviors of Castor Oil Based PU/PS Interpenetrating Polymer Network-Metakaolin Composites

The meta kaolin (MK) clay particulate filler with different weight ratios viz., 0, 5, 10, 20 and 30 wt% were incorporated into castable polyurethane (PU)/polystyrene (PS) (90/10) interpenetrating polymer network (IPN). The effects of MK particulate filler loading on the mechanical and thermal properties of PU/PS (90/10) IPN composites have been studied. From the tensile behavior, it was noticed that a significant improvement in tensile strength and tensile modulus as an increase in MK filler content. Thermogravimetric analysis (TGA) data reveals the marginal improvement in thermal stability after incorporation of MK filler. TGA studies of the IPN composites have been performed in order to establish the thermal stability and their mode of thermal degradation. It was found that degradation of all composites takes place in two steps. Degradation kinetic parameters were obtained for the composites using three mathematical models. Tensile fractured composite specimens were used to analyze the morphology of the composites by scanning electron microscopic (SEM) technique.     

聚丙烯酸酯/偏二氯乙烯/蒙脱土复合乳液的制备

以偏二氯乙烯和蒙脱土作改性剂,采用种子乳液聚合方法制备了聚丙烯酸酯 偏二氯乙烯/蒙脱土（PEA VDC/MMT）共聚物复合乳液,研究了蒙脱土质量分数对共聚物乳胶粒径、乳胶膜抗拉强度与断裂伸长率及热稳定性的影响。 结果表明,当蒙脱土质量分数从1%增加至5%时,PEA-VDC/MMT共聚物乳胶的平均粒径从141 nm增至243 nm;在蒙脱土质量分数为2%时, 乳胶膜的拉伸强度和断裂伸长率达到最大值,分别为3.23 MPa和1.330%。 PEA VDC共聚物的成碳率和热分解温度均随蒙脱土质量分数的增加而略有增加。     

Evolution of nanometer voids in polycarbonate under mechanical stress and thermal expansion using positron spectroscopy

Positron Annihilation Lifetime Spectroscopy (PALS) measurements were conducted on polycarbonate subjected to either thermal expansion or to tensile and compressive strains. It was found that thermal expansion affected both the nanometer hole size and the hole number density, whereas mechanical stress affected mainly the size of existing holes, and did not generate or eliminate holes in the quasielastic deformation region. The effect of stress on yield and postyield behavior of this glassy material was also investigated. The deduced hole volume fraction of this polymer at 25°C was 6.8 ± 0.5% from the thermal expansion experiment and 7.2 ± 1.2% from the mechanical loading experiment. When the specimen was under compression, the hole volume fraction was found to continuously decrease. This can be considered as evidence of the inability of the free volume concept in explaining the yield behavior of glassy polymers. ©1995 John Wiley & Sons, Inc.     

Effect of strain rate on the dynamic tensile behaviour of UHMWPE fibre laminates

Ultra-high molecular weight polyethylene (UHMWPE) fibre has great potential for strengthening structures against impact or blast loads. A quantitative characterization of the mechanical properties of UHMWPE fibres at varying strain rates is necessary to achieve reliable structural design. Quasi-static and high-speed tensile tests were performed to investigate the unidirectional tensile properties of UHMWPE fibre laminates over a wide range of strain rates from 0.0013 to 163.78 s⁻¹. Quasi-static tensile tests of UHMWPE fibre laminates were conducted at thicknesses ranging from 1.76 mm to 5.19 mm. Weibull analysis was conducted to investigate the scatter of the test data. The failure mechanism and modes of the UHMWPE fibre laminates observed during the test are discussed. The test results indicate that the mechanical properties of the UHMWPE fibre laminate are not sensitive to thickness, whereas the strength and the modulus of elasticity increase with strain rate. It is concluded that the distinct failure modes at low and high strain rates partially contribute to the tensile strength of the UHMWPE fibre laminates. A series of empirical formulae for the dynamic increase factor (DIF) of the material strength and modulus of elasticity are also derived for better representation of the effect of strain rate on the mechanical properties of UHMWPE fibre laminates.     

Superhydrophilic functionalized graphene/fiberglass/epoxy laminates with high mechanical,impact and thermal performance and treated by plasma

This research aims to develop superhydrophilic fiberglass/epoxy nanocomposite (FGEC) laminates with high mechanical, thermal, and impact properties. In order to achieve this goal, functionalized graphene (FGA) was used as a nanofiller material to improve the mechanical, impact, and thermal behaviors of FGEC, while the plasma treatment helped to form the oxidized polar functional groups (C9O groups and C–O groups) on the fabricated FGEC laminates, thus modifying their hydrophilic behavior. The experiments were started with production of FGEC laminates by mixing FGA (0.05-0.4 wt%) with epoxy resin in presence of Acetone (to obtain better dispersion), followed by preparation of FGEC laminates using vacuum-assisted resin transfer and curing processes. Afterwards, the surfaces of the fabricated FGEC laminates were treated by air plasma at 13Pa and 30W for different treatment times in the range 5–30 min. Mechanical and impact properties of the untreated and treated laminates were investigated according to ASTM-D7025 and ISO 6603-2 standards, respectively. Also, thermal behavior of the laminates was investigated using a thermogravimetric analysis, while a high resolution camera was used to record and calculate a contact angle of the untreated and treated laminates. SEM and Optical Microscope was used to observe dispersion of FGA, microstructure, impact mechanism, and surface morphology of the fabricated FGEC matrix. Meanwhile, XPS was used to evaluate changes in the surface structures of the untreated and treated samples. The results showed that 0.35 wt% of FGA and 15-min exposure to plasma treatment were enough to improve tensile strength and impact energy of the laminates by 18% and 70%, respectively, and to decrease the water contact angle from 67° to 14°.     

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.     

Evaluation of gamma camera collimator for regional cerebral blood flow measurements using a 133Xe inhalation method

In the measurements of regional cerebral blood flow (rCBF) using inhalation of 133Xe gas, the activity present is generally limited in lower levels than those of usual brain scintigraphy. Measurements with low count-rate are usually resulted in diminishing the accuracies of results obtained. Therefore, it is necessary to make measurements using a high sensitive collimator for getting as much count-rate as possible when a gamma camera is used. The relationships among sensitivity and structures of multi-parallel collimator were mathematically analyzed. The results of analysis suggested that sensitivity usually increased by using a collimator with holes of reduced height and diameter. A prototype multi-parallel collimator with holes of low height and small diameter was made in our laboratory for testing sensitivity and resolution. The collimator possessing 1141 holes of 6 mm phi in hole diameter, 1.5 cm is hole height and septal thickness of 1 mm lead showed 24 times more sensitive than those of a general all purpose collimator supplied by the manufacturer. However, resolution measured in FWHM was of 9 to 14 mm at the collimator face and of 29 to 38 mm at 5 cm from the face. The results indicated that this collimator was useful enough in rCBF measurements with 133Xe inhalation using a gamma camera. The mathematical analysis however, suggested that optimum collimator for rCBF measurements was approximate 4.5 mm phi in hole diameter and 1.0 cm in hole height.     

Degradation of ROMP-based bio-renewable polymers by UV radiation

The degradation of a bio-renewable polymer under UV exposure was studied using various methods. Degradation of the bio-renewable polymer increased with increasing exposure time. Enhanced cross-link density in the early stage of degradation was confirmed by Soxhlet extraction. Tensile testing showed a transition from ductile failure to brittle fracture. Surface cracks and embrittlement were primary reasons for most reductions in mechanical properties, such as tensile strength and breaking strain. The effects of degradation were confined to the surface of thick bio-based polymer specimens, confirmed by both SEM and PAS-FTIR. Depth profile studies of degraded samples showed that the concentration of oxidation products, such as hydroxyl and carbonyl groups, varied with depth depending on the diffusion of oxygen.     

Effects of Wood Flour (WF) Pretreatment and the Addition of a Toughening Agent on the Properties of FDM 3D-Printed WF/Poly(lactic acid) Biocomposites

In order to improve the properties of wood flour (WF)/poly(lactic acid) (PLA) 3D-printed composites, WF was treated with a silane coupling agent (KH550) and acetic anhydride (Ac₂O), respectively. The effects of WF modification and the addition of acrylicester resin (ACR) as a toughening agent on the flowability of WF/PLA composite filament and the mechanical, thermal, dynamic mechanical thermal and water absorption properties of fused deposition modeling (FDM) 3D-printed WF/PLA specimens were investigated. The results indicated that the melt index (MI) of the specimens decreased after WF pretreatment or the addition of ACR, while the die swell ratio increased; KH550-modified WF/PLA had greater tensile strength, tensile modulus and impact strength, while Ac₂O-modified WF/PLA had greater tensile modulus, flexural strength, flexural modulus and impact strength than unmodified WF/PLA; after the addition of ACR, all the strengths and moduli of WF/PLA could be improved; after WF pretreatment or the addition of ACR, the thermal decomposition temperature, storage modulus and glass transition temperature of WF/PLA were all increased, and water absorption was reduced.     

醋酸环境对醋酸胶片物理性能的影响研究

醋酸胶片的片基材料醋酸纤维素酯水解产生的"醋酸综合症"是影像部门保存醋酸胶片过程中遇到的最大技术难题之一,目前还没有较好的治理方法,其在降解过程中释放出的醋酸严重影响胶片的耐久性,关于其物理性能变化及相关性的研究较少.本文通过模拟密闭环境中醋酸浓度的累积实验,系统地分析了醋酸在胶片降解过程中对胶片物理性能的影响.实验结果表明,醋酸环境会加速胶片的降解,且随着醋酸浓度的增加,胶片扭曲变形程度增加,胶片的降解程度(酸度)增加;抗张强度减弱,但耐折度增加;含湿量和胶片乳剂层面的亲水性增加,同时胶片的热稳定性变差.     

Preparation and Properties of Biodegradable Spent Tea Leaf Powder/Poly(Propylene Carbonate) Composite Films

The aim of the present work is to develop novel bio-based lightweight material with improved tensile and thermal properties. Spent tea leaf powder (STLP) was used as a filler to improve the tensile and thermal properties of polypropylene carbonate (PPC). Tea is an important material used in hotels and households, and spent tea leaf is a resulting solid waste. Composite films with STLP were obtained by the solution casting method. These films were characterized by optical and scanning electron microscopy, Fourier transform-infrared spectroscopy, thermogravimetric analysis, and tensile testing to examine the effect of filler content on the properties of the composites. The results showed that composite films have increased tensile strength due to enhanced interfacial adhesion between the filler and the matrix. In addition, the composite films also exhibited higher thermal degradation temperatures than pure polypropylene carbonate. The morphology results indicate that there is a good interface interaction between STLP and PPC. Results of the study reveal STLP to be a promising green filler for polymer plastics.     

Heterogeneous thermal excitation and relaxation in supercooled liquids

We investigate a phenomenological model which rationalizes the effects of dielectric hole burning on the basis of heterogeneous dielectric and specific heat relaxation in supercooled liquids. The quantitative agreement between model predictions and dielectric hole-burning observations is lost if the assumption of correlated dielectric and thermal relaxation times is removed from the model. This suggests that dynamically distinct domains in real liquids are associated with a time constant which characterizes both the structural and thermal relaxation behaviors. The calculations demonstrate that the observed burn-induced modifications reflect the spectral selectivity and persistence time of the fictive temperatures within these domains, and that 100 or more cycles of the sinusoidal burn field can be required to saturate the heat accumulated in the slow degrees of freedom. It is also shown that the recovery of dielectric holes is entirely accounted for by the model, and that the persistence times do not provide direct insight into rate exchange processes. Additionally, the model predicts that the heating effects considered here are a significant source of nonlinear dielectric behavior, even in the absence of deliberate frequency selective hole burning.     

Enhanced mechanical properties of unidirectional basalt fiber/epoxy composites using silane-modified Na+-montmorillonite nanoclay

This study explores the effects of 3-glycidoxypropyltrimethoxysilane (3-GPTS) modified Na-montmorillonite (Na-Mt) nanoclay addition on mechanical response of unidirectional basalt fiber (UD-BF)/epoxy composite laminates under tensile, flexural and compressive loadings. Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and simultaneous thermal analysis (STA) data confirmed the reaction mechanism between the silane compound and Mt. It was demonstrated that addition of 5 wt % 3-GPTS/Mt resulted in 28%, 11% and 35% increase in flexural, tensile and compressive strengths. Scanning electron microscopy (SEM) clarified the improvement in the adhesion between the basalt fibers and matrix in the case of Mt-enhanced epoxy specimens. Also, a theoretical route based on a Euler-Bernoulli beam-based approach was employed to estimate the compressive properties of the composites. The results demonstrated good agreement between theoretical and experimental approaches. Totally, the results of the study show that matrix modification is an effective strategy to improve the mechanical behavior of fibrous composites.     

Evaluation of magnesium sulphate attack in mortar-metakaolin system by thermal analysis

This paper reports an experimental study on the magnesium sulphate resistance of mortar specimens incorporating 0, 10 and 20% of metakaolin (MK). The evidence of the attack was evaluated through the content of calcium hydroxide (portlandite) and formation of magnesium hydroxide (brucite) by thermal analysis (thermogravimetric and derivative thermogravimetric analysis). The mechanical degradation of the mortar specimens was evaluated through splitting tensile tests after 200 days of exposition to the magnesium solution. The addition of metakaolin resulted in a reduction in the content of calcium hydroxide and in a smaller formation of brucite in comparison with reference mixture. A tensile strength loss of about 7% was observed for the metakaolin mortars submitted to the magnesium solution attack for 200 days.     

Mechanical,thermal, and morphological properties of powder coating waste reinforced acetal copolymer

The present study investigates the individual effects of three different thermosetting waste materials, used as fillers, on the mechanical, thermal and flow properties of acetal copolymers (POM). Different amounts ranging from 5% to 30% by weight of hydrolyzed powder coating recyclates were mixed as filler material in POM. The matrix and the fillers were first dry-mixed and then compounds were prepared through melt extrusion. The resulting compounds were cooled, granulated, and then standard tensile test bars were produced through use of an injection-molding machine. We investigated the mechanical and thermal properties of test specimens, and tensile strength, bending strength and impact strength were evaluated as a function of type and amount of filler material in the POM matrix. In addition, the change in melt flow index of POM/filler mixtures was determined, before and after extrusion. Furthermore, the morphology of the specimens was examined via electron microscopy. The results of this investigation are encouraging and present an innovative approach to reutilize hydrolyzed electrostatic powder coating wastes with thermoset structures as fillers in acetal copolymers.