Mechanical and thermal properties of high‐density polyethylene toughened with glass beads

Glass beads were used to improve the mechanical and thermal properties of high‐density polyethylene (HDPE). HDPE/glass‐bead blends were prepared in a Brabender‐like apparatus, and this was followed by press molding. Static tensile measurements showed that the modulus of the HDPE/glass‐bead blends increased considerably with increasing glass‐bead content, whereas the yield stress remained roughly unchanged at first and then decreased slowly with increasing glass‐bead content. Izod impact tests at room temperature revealed that the impact strength changed very slowly with increasing glass‐bead content up to a critical value; thereafter, it increased sharply with increasing glass‐bead content. That is, the Izod impact strength of the blends underwent a sharp transition with increasing glass‐bead content. It was calculated that the critical interparticle distance for the HDPE/glass‐bead blends at room temperature (25°C) was 2.5 μm. Scanning electron microscopy observations indicated that the high impact strength of the HDPE/glass‐bead blends resulted from the deformation of the HDPE matrix. Dynamic mechanical analyses and thermogravimetric measurements implied that the heat resistance and heat stability of the blends tended to increase considerably with increasing glass‐bead content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2102–2107, 2003     

Fabrication of large‐scale superhydrophobic composite films with enhanced tensile properties by multinozzle conveyor belt electrospinning

Large‐scale superhydrophobic composite films with enhanced tensile properties were prepared by multinozzle conveyor belt electrospinning. First, a strategy of conveyor belt electrospinning was introduced for large‐scale fabrication since the conveyor belt can expand the electrospinning area unlimitedly. During the electrospinning (or electrospraying) process, certain kinds of fibers are combined on the conveyor belt in one electrospinning (or electrospraying) step. The superhydrophobicity of electrospun film can be achieved by the presence of PS beads and bead‐on‐string PVDF fibers, while submicron PAN fibers are responsible for the improvement of mechanical properties. The result shows that CA value of the surface comprising of PS beads and bead‐on‐string PVDF fibers could reach up to 155.0°. As the submicron PAN fibers increased, the value of CA decreased, changing from 155.0° to 140.0°, meanwhile the tensile strength of composite film was enhanced from 1.14 to 4.12 MPa correspondingly which is beneficial to putting the films into practice. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39735.     

耐热钢15CrMoR的焊接工艺研究

针对某公司的高压加氢反应器产品,对厚度为38mm的15CrMoR进行了焊接工艺评定。焊接方法采用钨极氩弧焊(GTAW)打底+焊条电弧焊(SMAW)填充盖面,焊后进行热处理。对焊接接头的拉伸强度、弯曲、冲击及硬度等性能进行了测试。测试结果表明,焊接接头的拉伸强度可达510 MPa以上,侧弯180°后未见裂纹产生;在-20℃的条件下,焊缝的冲击功可达46J以上,热影响区的冲击功可达42J以上;焊缝的平均硬度值为176HBW,热影响区的平均硬度值为190HBW。各项性能均可满足要求。     

Evaluation of heat treatment regimes and their influences on the properties of powder‐printed high‐density polyethylene bone implant

A two‐step heat treatment was utilized as a means to improve the mechanical properties of a high‐density polyethylene structure which was fabricated using the three‐dimensional printing technique. It was found that the relationship between structure and properties was strongly influenced by heat treatment conditions including treatment times (15–60 min) and treatment temperatures (140–180 °C) of both primary and secondary steps. The use of primary heating at 180 °C for 15 min and secondary heating at 160 °C for 60 min resulted in the highest tensile modulus and strength, 0.7 GPa and 14.8 MPa, respectively. The changes in both shrinkage and tensile properties were governed by the level of residual porosity and quality of polyethylene interface in samples which were both influenced by the degree of thermally induced densification and binder degradation. Empirical correlations between porosity and shrinkage or tensile properties were found to be power functions. Copyright © 2010 Society of Chemical Industry     

Dynamic mold surface temperature control using induction heating and its effects on the surface appearance of weld line

Electromagnetic induction heating combined with coolant cooling is used to achieve dynamic mold surface temperature control. A simulation tool was also developed by integration of both thermal and electromagnetic analysis modules of ANSYS, and capability and accuracy were verified experimentally. To evaluate the feasibility and efficiency of induction heating on the mold surface temperature control, a mold plate (roughly about an inset size of cellular phone housing) with four cooling channels was utilized for two demo experiments with varying mold surface temperature between 110 and 180°C, and 110 and 200°C, respectively. During induction heating/cooling, it takes 4 s to increase mold surface temperature from 110 to 200°C and 21 s for mold surface to return to 110°C. The mold plate surface temperature can be raised at about 22.5°C and cooled down at 4.3°C/s within the aforementioned temperature range. Mold plate temperature distribution exhibits good uniformity as well in all stages of the heating/cooling process. Finally, mold surface temperature of a double‐gated tensile test part mold was induction heated to above glass transition temperature for few seconds prior to melt injection. The surface mark of weld line was eliminated, and the associated weld line strength enhanced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1174–1180, 2006     

Evaluation of Polymethylmethacrylate Cohesion Behavior with a Gas-Assisted Thermal Bonding Method

By applying heat and pressure to thermoplastic materials, the overlap of the two pieces can be bonded to form hermetic systems. Polymethylmethacrylate (PMMA) is a thermoplastic used in commercial microfluidic devices; its advantages include low cost, ready fabrication, and high transparency. In order to gain an understanding of PMMA's relevant characteristics (thermal behavior, material strength, and hermetic sealing strength), we study its bulk properties and mechanical behavior. Experimental results of the cohesion behavior of PMMA sheets were collected and are presented here. Samples were bonded by subjecting a sample to elevated pressure and temperature in the glass transition range (85°C–165°C), which was determined beforehand by differential scanning calorimetry and literature. Five different bonding temperatures (140°C, 150°C, 160°C, 170°C, and 180°C) and three bonding pressures (1.2, 1.4, and 1.6 MPa) were applied for making samples; mechanical strength tests were then carried out to understand separately the bulk mechanical strength and the interfacial properties (shear strength and bonding strength) of a cohesive laminate at the temperatures near the glass transition range. POLYM. ENG. SCI., 60:161–167, 2020. © 2019 Society of Plastics Engineers     

Microwave welding of high density polyethylene using intrinsically conductive polyaniline

The use of intrinsically conductive polymers in welding of plastics and composites offers the possibility of developing new welding methods. Intrinsically conductive polyaniline (PANI) composite gaskets were used to microwave weld high density polyethylene (HDPE) bars. Two composite gaskets were made from a mixture of HDPE and PANI powders in different proportions. Adiabatic heating experiments were used to estimate the internal heat generation and electric field strength in the gasket. During welding, the effects of heating time, heating pressure and welding pressure were evaluated. It was found that increasing the heating time and the welding pressure increased the joint strength. The maximum tensile joint strength was achieved using a 60 wt% PANI gasket with a heating time of 60 sec and a welding pressure of 0.9 MPa; this resulted in a tensile weld strength of 24.79 ± 0.34 MPa, which equals the tensile strength of the bulk HDPE.     

Mechanical properties of fusion welded ceramics in the SiC-ZrB2 and SiC-ZrB2-ZrC systems

Mechanical properties of welded SiC-ZrB₂ and SiC-ZrB₂-ZrC ceramics were measured up to 1700 °C. Commercial powders were hot pressed, machined into coupons, and preheated to 1600 °C before joining the ceramics using either tungsten inert gas welding or plasma arc welding. Toughness of the parent materials was 3–4 MPa*m^1/2 which decreased after welding to 2–2.5 MPa*m^1/2. Strength of the SiC-ZrB₂-ZrC parent material was ~700 MPa at 25 °C, ~300 MPa at 1700 °C, and retained 40–60% of this strength once welded. Strength of the SiC-ZrB₂ parent material was ~600 MPa at 25 °C and 1700 °C and retained 20–30% of this strength once welded. Griffith analysis indicated that the strength in the parent materials was controlled by the size of SiC clusters while strength of welds was controlled by the size of pores in fusion zones. Therefore, removal of pores in produced fusion zones should be investigated to improve strength of future ceramic welds.     

Effect of silicone resin on the properties of silica ceramic cores by heating treatment

Silica ceramic cores prepared by heat-press molding were strengthened by impregnating silicone resin. The effect of heating treatment conditions on the properties of silica ceramic cores was analyzed. Results showed that the ambient bending strength increased from 9.3 ± 2.0 MPa to 24.8 ± 1.5 MPa by curing process at low temperature of 250 °C. However, further heating treatment at high temperature ranging from 1150 to 1300 °C made the strength of the samples lower than that of the cured samples owing to the decomposition of silicone resin. But the strength of the samples was still higher than that of raw samples. The increasing heating treatment temperature promoted an increase in the strength by a densification process.     

改性空心玻璃微珠/环氧树脂复合材料力学性能研究

采用偶联剂对玻璃微珠表面进行改性处理,借助超声波振动,使改性空心玻璃微珠在环氧树脂中均匀、稳定分散,增强了玻璃微珠与环氧树脂之间的相容并探讨了改性空心玻璃微珠对环氧树脂力学性能的影响。结果表明,复合材料中改性空心玻璃微珠添加质量分数为3%时,其拉伸强度达到最大值68.54 MPa,与空白样相比提高了20.3%;冲击强度达到最大值24.42 kJ/m2,比纯环氧树脂提高了166%;KIC(断裂韧性)达到最大值2.338 MPa/m2,是空白试样的2.27倍,增韧效果较为明显。     

Thermal post-processing effects on the polycarbonate acrylonitrile butadiene styrene composites manufactured by fused filament fabrication

The mechanical properties of components manufactured by fused filament fabrication lack sufficient levels for industrial applications. The need for post-processing is, therefore, necessary to enhance the interlayer strength and mechanical characteristics. In the present study, experimental analysis of the effects of annealing on polycarbonate acrylonitrile butadiene styrene manufactured by fused filament fabrication is explored. Annealing temperatures are selected in the range from 90 to 210°C based on differential scanning calorimetry analysis. The ultimate tensile strength improved by 20.39% from 32.39 to 38.99 MPa after the heat treatment at 180°C for 1-h duration. Flexural strength showed a remarkable enhancement of 53.21% after annealing at 180°C for 2 h. The interlayer diffusion and bonding are boosted following heat treatment and microstructural imaging proved the same although the surface had flakes due to the high heat exposure. X-ray diffraction testing of annealed models demonstrated a maximum crystallinity index of 32.56% when compared with nonannealed samples with 6.58%. The addition of polycarbonate to acrylonitrile butadiene styrene improves the stiffness and impact loading capacity with high heat resistance. The heat treatment process is capable of magnifying the mechanical characteristics of the end functional components, thereby opening up the scope for more engineering applications.     

Interfacial and thermomechanical characterization of reaction formed joints in silicon carbide-based materials

The microstructure and mechanical properties of reaction formed joints of Refel^TM reaction bonded SiC (RB-SiC) and Hexoloy^TM sintered SiC were studied in order to achieve a better understanding of the influence of base materials and joining process parameters on the high temperature strength of reaction formed joints. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical microscopy were used to characterize the joints prior to mechanical tests. The microstructural analysis indicated that the joints consist of silicon carbide (SiC) grains (with grain sizes ranging from 0.1 to 2 μm) and crystalline silicon as an intergranular phase. Most of the silicon carbide grains in the joint have hexagonal crystal structure with certain preferential orientations related to the silicon matrix. The high temperature strength of joints was measured by constant strain rate experiments in compression where joints were forming 45° with the compression axe. The strength of the joined Refel RB-SiC has been found to be at least equal to that of the bulk materials (550 MPa at 1235°C and 400 MPa at 1385°C). The joined Hexoloy specimens had strengths (1.4 GPa at 1290°C and 750 MPa at 1420°C) lower than the bulk material but higher than the joints of RB-SiC.     

High-toughness mullite ceramics fabricated by hot-press sintering of pyrophyllite and AlOOH at low temperatures

High-toughness mullite ceramics were fabricated through hot-press sintering (HPS) of pyrophyllite and AlOOH, which were wet-milled and well mixed using a planetary ball mill. The impacts of sintering temperatures and contents of AlOOH on mullite phase formation, densification, microstructure and mechanical properties in ceramic materials were investigated through XRD, SEM and mechanical properties determination. The results indicated that high-toughness mullite ceramics could be successfully prepared by HPS at temperatures higher than 1200°C for 120 min. Increasing the sintering temperature from 1000 to 1300°C significantly enhanced the flexural strength and fracture toughness of samples. The highest flexural strength of 297.97±25.32 MPa and fracture toughness of 4.64±0.11 MPa⋅m^1/2 were obtained for samples sintered at 1300°C. Further increase of temperature to 1400°C resulted in slight decrease of flexural strength and fracture toughness. Compared with the mullite ceramics prepared only using pyrophyllite as raw material, incorporation of AlOOH into raw material significantly increased the mechanical properties of final mullite ceramics. And stoichiometric AlOOH and pyrophyllite as starting material gave the best performance in fracture toughness. The high-toughness of mullite ceramics were ascribed to the high mullite phase content, fine mullite whiskers and in situ formed, intertwined three-dimensional network structure obtained through HPS at a low temperature of 1300°C.     

Microcosmic morphology and properties of hollow glass beads‐reinforced polylactic acid–based foam composites

Polylactic acid (PLA)–based foam composites reinforced with hollow glass beads (HGBs) were prepared via a two‐step process. First, the glass beads, PLA, foaming agent, and other additives were blended, supplanted, and pelletized. Second, the foaming masterbatch was introduced into the mold using thermocompressor to make the microfoam composites. The foam morphology, mechanical properties, and heat resistance were investigated. The experimental results show that the compressive strength of the composites achieved an optimal value when the mass fraction of HGBs was 15%, and that the elastic modulus of the composites increases with increasing bead contents. In addition, after doing a comparative analysis of composites with different bead contents, it was discovered that the foam morphology quality became more uniform and fine with the addition of the beads. Finally, it was found that inclusion of the beads enhanced the thermal stability of the composites and improved their thermal decomposition temperature by about 50°C. POLYM. COMPOS., 37:692–699, 2016. © 2014 Society of Plastics Engineers     

聚乙烯管道热熔接头卷边对拉伸性能的影响

通过拉伸试验,研究了聚乙烯管道热熔对接接头不同卷边情况试样的失效形式、拉伸强度和拉伸历程。研究发现,带卷边试样卷边与管壁之间形成的凹槽尖端应力集中严重,拉伸时裂纹逐渐扩展直至试样断裂;而不带卷边试样拉伸时,试样发生大变形后在焊缝及其与管材交界面出现脆断现象。不带卷边试样的拉伸强度明显高于带卷边试样,其断裂伸长率也远高于带卷边试样,拉伸速率为10 mm/min时,拉伸强度差值在27 ％左右,断裂伸长率差值在100 ％以上。结果表明,去除热熔对接接头双侧卷边可显著提高其拉伸力学性能,而去除单侧卷边对其力学性能仅有轻微改善。     

Impact of preheating on the mechanical performance of different MgO-C bricks—Intermediate temperature range

This work analyses the mechanical behavior of MgO-C refractories at an intermediate temperature of 1000 °C. Conditions similar to those occurring during the in-service pre-heating of steelmaking ladles are simulated by thermal treatment before the mechanical testing. Stress-strain curves were determined under compressive loading at RT and 1000 °C. The impact of the thermally activated physicochemical transformations on the mechanical response of the materials was evaluated in terms of parameters such as strength, fracture deformation, secant modulus and yield strength. The presence of Al seems to be deleterious when longer soaking times at 1000 °C were applied, which was attributed to the progressive damage related to in situ phase formation. On the other hand, when heating these types of refractories simultaneously with the application of a low compressive load, the closure of previously formed microcracks (self-healing) was considered to be mainly responsible for their mechanical behavior.     

Improved weld strength of vibration welded polyoxymethylene/multiwalled carbon nanotubes hybrid nanocomposites

In this study, carbon nanotubes reinforced polyoxymethylene with different filler loadings was joined by using linear vibration welding technique. The tensile properties of vibration welded polyoxymethylene nanocomposites with different carbon nanotube contents were studied as functions of filler loading and weld pressure. The results showed that the addition of carbon nanotubes into polyoxymethylene slightly improved the matrix tensile strength and pronounced decreased the ductility of pure polyoxymethylene. Interestingly, the weld strength of the nanocomposites was also higher than the polymer matrix strength even at high weld pressure of 2 MPa. Possible reasons for this high weld strength are discussed based on the morphological investigations. POLYM. ENG. SCI., 56:636–642, 2016. © 2016 Society of Plastics Engineers     

Enhancing the physical and mechanical properties of pellet-shaped hydroxyapatite by controlling micron- and nano-sized powder ratios

Hydroxyapatite (HA) was fabricated in microns as its basic size. The particle size distribution was controlled by mixing micron- and nano-sized HA to obtain the optimum amount of mixture to improve its properties. HA powder with a size of 2.5 μm was mixed with that with a size of 200 nm, with a variety of concentrations of up to 20 wt%. A green body was fabricated using the uniaxial pressing method at a pressure of 200 MPa. The sintering process was conducted at a temperature of 1200 °C, heating rate of 3 °C/min, and holding time of 2 h in air. The physical characteristics of the HA sintered body were determined using X-ray diffraction, scanning electron microscopy, linear shrinkage, and density testing. The mechanical properties of the HA sintered body were tested using compressive strength testing. The test results indicated that the mechanical properties of the HA sintered body increased with the addition of nano-sized HA. The mechanism of the increasing strength occurred because nano-sized HA particles filled the gaps between the micron-sized particles. In this study, the highest mechanical properties were obtained by adding 20 wt% nano-sized HA. The compressive strength in the sample without added nano-sized HA was 132.2 MPa and increased significantly to 208.6 MPa with the addition of nano-sized HA of 20 wt%. No change in the phase in HA was observed within a sintering temperature of 1200 °C.     

Mechanical and thermal properties of glass bead–filled nylon‐6

The mechanical and thermal properties of glass bead–filled nylon‐6 were studied by dynamic mechanical analysis (DMA), tensile testing, Izod impact, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) tests. DMA results showed that the incorporation of glass beads could lead to a substantial increase of the glass‐transition temperature (T_g) of the blend, indicating that there existed strong interaction between glass beads and the nylon‐6 matrix. Results of further calculation revealed that the average interaction between glass beads and the nylon‐6 matrix deceased with increasing glass bead content as a result of the coalescence of glass beads. This conclusion was supported by SEM observations. Impact testing revealed that the notch Izod impact strength of nylon‐6/glass bead blends substantially decreased with increasing glass bead content. Moreover, static tensile measurements implied that the Young's modulus of the nylon‐6/glass bead blends increased considerably, whereas the tensile strength clearly decreased with increasing glass bead content. Finally, TGA and DSC measurements indicated that the thermal stability of the blend was obviously improved by incorporation of glass beads, whereas the melting behavior of the nylon‐6 remained relatively unchanged with increasing glass bead content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1885–1890, 2004     

Synthesis and microstructure evolution of WCoB based cermets during spark plasma sintering

WCoB based cermets were prepared by spark plasma sintering at sintering temperature among 600°C-1200 °C. The phase evolution was investigated by detecting density behavior, phase composition, microstructure and mechanical properties during sintering process. The sintering process can be divided into three stages: powder densification, solid phase reaction and liquid phase sintering. WCoB hard phase forms at 1000 °C during solid phase sintering, showing better mechanical properties than Co₂B, especially on Vicker's hardness. WCoB hard phase forms on the basis of Co₂B binary boride and its content increases in liquid phase sintering stage with high density. The Vicker's hardness and transverse rupture strength (TRS) reach the maximum value of 1262 Hv and 1212 MPa at 1200 °C and 1170 °C, respectively. The fracture toughness reaches the maximum value of 21.8 MPa m^1/2 at 1050 °C, and the inter-granular fracture is the main fracture mechanism.