Melt Vibration Improved Melt Flow Behavior and Mechanical Properties of High Density Polyethylene

A pulse pressure was superimposed on the melt flow resulting in melt vibration. With application of the melt vibration technology, the melt flow behavior and mechanical properties of high‐density polyethylene were studied. For vibration‐assisted extrusion (VAE) at constant vibration pressure amplitude, the viscosity decreases sharply with increasing vibration frequency, and also does so when increasing vibration pressure amplitude for VAE at constant vibration frequency. The effect of vibration field on melt rheological behavior is also related to the melt temperature; a large decease in viscosity is obtained at low melt temperature. Compared with the mechanical properties obtained by conventional injection molding (CIM), the mechanical properties for vibration‐assisted injection molding (VAIM) samples were improved by changing the vibration frequency and vibration pressure amplitude. Injected at constant low vibration pressure amplitude, the VAIM sample prepared at high vibration frequency shows large elongation at break; injected at constant low vibration frequency, the VAIM sample prepared at high vibration pressure amplitude shows greatly improved yield strength. The above two VAIM processing routes produce different VAIM samples with different fracture behaviors; a distinct layered structure for VAIM samples was observed by SEM.     

Biaxially Self-Reinforced High-Density Polyethylene Prepared by Vibration-Assisted Injection Molding. I. Processing Conditions and Physical Properties

A pulse pressure was imposed on the melt in the injection molding cavity during the injection and holding pressure stages, called vibration-assisted injection molding (VAIM) technology. With the VAIM technology, biaxially self-reinforced high-density polyethylene (HDPE) samples were prepared and the physical properties affected by the vibration processing conditions were studied. The tensile properties can be improved in both the machine direction (MD) and the transverse direction (TD) by changing the vibration frequency and vibration pressure amplitude, respectively. The elongation at break increased with increasing the vibration frequency for the VAIM sample processed at constant low vibration pressure amplitude; the yield strength increased with increasing the vibration pressure amplitude for the VAIM sample prepared at constant low vibration frequency. The softening point temperature for the VAIM sample increased by 8°C compared with a conventional injection-molded (CIM) sample.     

The β - and γ -Form Distributions of Isotactic Polypropylene Injection Molding Controlled via Melt Vibration

The effect of melt vibration on the crystal form of isotactic Polypropylene (iPP) samples prepared by low-frequency Vibration-Assisted Injection Molding (VAIM) was investigated. The distribution of crystal forms through the thickness was investigated under different VAIM processing conditions, with Conventional Injection Molding (CIM) for comparison. Wide-Angle X-ray Diffraction (WAXD) showed that the content of β -form crystals decreases from the surface to the core region in the CIM and VAIM samples. The β -form distribution through the thickness is controlled by the VAIM processing conditions. The occurrence of γ -form crystals was found in the VAIM samples produced at relatively low vibration frequency and relatively large pressure vibration amplitude.     

Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

Ferritic steel with compositions 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B), 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) (all in wt%) each with a 1.0?wt% nano-Y₂O₃ dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000°C using a 75-MPa uniaxial pressure applied for 5?min and a 70-kA pulse current at 3?Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus were determined using a micro/nano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850–2850?MPa), yield strength (500–1556?MPa), Young's modulus (175–250?GPa) and nanoindentation hardness (9.5–15.5?GPa), with up to 1–1.5 times greater strength than other oxide dispersion-strengthened ferritic steels (<1200?MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10–20-nm Y₂Ti₂O₇ or Y₂O₃ particles in a high-alloy ferritic matrix.     

Strengthening in high-pressure quenched Zr

The present study examined the effects of pressure (range: 1–6?GPa) on microstructure and mechanical properties of pure Zr. Pressure significantly affected refining of Zr microstructure. When 5?GPa pressure was applied, ω-phase was observed in processed specimen, and volume fraction sharply increased to 57.4% for specimen pressurized-quenched at 6?GPa. Benefitting from refinement of acicular-shaped α (α′) plates and the formation of equiaxial ω-phase, the yield strength of the sample quenched from 6?GPa reached ～616?MPa, which is almost twice as that of coarse-grained Zr.     

Simultaneously Enhancing Mechanical Properties and Melt Flow Ability of Polyamide 6 by Blending with a Hyperbranched Polymer

A series of polyamide 6/hyperbranched polymers (PA6/HBP) blends with different HBP contents was prepared by melt processing using a twin-screw extruder. The HBP was synthesized on the basis of pentaerythritol and dimethyl terephthalate according to a one-step method. The melt flow behavior, crystallization behavior, morphology, and mechanical properties of the PA6/HBP blends were investigated. The results showed that the melt flow index of the blends was greatly improved by a small amount of HBP. The yield strength, tensile modulus, Izod impact strength, and flexural strength of samples were simultaneously enhanced from 54.6 MPa, 0.5 GPa, 3.8 kJ/m², 56.9 MPa for pure PA6 to 61.1 MPa, 0.7 GPa, 5.3 kJ/m², 67.1 MPa for PA6 blends with 2.0 wt% HBP, respectively. The PA6/HBP blends showed the higher content of α-form crystal and a higher degree of crystallinity than those of pure PA6.     

Self‐Toughening and Self‐Reinforcing Injection‐Molded Isotactic Polypropylene via Midfrequency Vibration Field

The effect of vibration frequency on the mechanical properties of general grade polypropylene (PP) prepared by two types of vibration injection molding (VIM) was investigated. With the application of vibration injection molding, the mechanical properties of isotactic PP are improved. The yield strength was upgraded with the increment of vibration frequency and a peak occurs at a particular frequency for each VIM. The elongation at break was also raised by increased vibration frequency, and the vibration frequency also improves impact strength. Self‐reinforcing and self‐toughening polypropylene molded parts were found at high vibration frequency. The wide angle X‐ray diffraction (WAXD) curves and scanning electronic micrograph (SEM) micrographs have shown that, in the vibration field, the enhancement of mechanical properties can be attributed to the occurrence of a γ‐phase crystalline structure and a more pronounced elongation in shape than obtained by conventional injection moldings. In addition, smaller crystals of the β‐phase crystal form improve toughness.     

The Effect of Melt Vibration on Polystyrene Melt Flowing Behavior During Extrusion

Vibration extrusion (VE) is achieved by superimposing a mechanical vibration on the flowing melt during extrusion. The effect of melt vibration on the melt flow behavior of polystyrene (PS) was studied. The melt flow behavior during conventional extrusion (CE) was studied for comparison. With the application of the melt vibration technology, the melt flow behavior of PS was greatly improved. The melt viscosity during the VE strongly depends on the vibration frequency and vibration amplitude. Extruded at constant vibration amplitude, the melt viscosity decreases sharply with increasing vibration frequency and also does so for increasing vibration amplitude when extruded at a constant vibration frequency. The improved melt flow property is explained in terms of shear-thinning criteria. The effect of melt vibration on the melt flow behavior is also related to the melt temperature and extrusion pressure; the greatest decease in viscosity is obtained at low temperature and low extrusion pressure.     

Improving Melt Flow Behavior via Melt Vibration

A self‐made melt vibration extrusion device was used to study the melt flow behavior in a vibration field. A pulse pressure was superimposed on the flowing melt during extrusion, called vibration assisted extrusion (VAE); conventional extrusion (CE) was studied for comparison. A die (L/D=17.5) was attached to the device to study melt flow behavior of an amorphous polymer (polystyrene) and semi‐crystalline polymers (high density and linear low polyethylene). Results show that the melt vibration technique is an effective processing tool to improve polymer melt flow behavior for both crystalline and amorphous polymers. Increasing with vibration frequency for extrusion at constant vibration pressure amplitude, the viscosity decreases sharply, and also with increasing vibration pressure amplitude at a constant vibration frequency. The effect of vibration field on melt flow behavior depends greatly on the melt temperature, with the largest change in viscosity obtained at low temperature. Increasing with vibration frequency at constant pressure vibration amplitude, the maximum decrease percentages of viscosities are 82.9, 66.7, and 48.9%, for HDPE, LLDPE, and PS, respectively; increasing with pressure vibration amplitude at a constant vibration frequency, the maximum decrease percentage of viscosities are 99.0, 94.3, and 99.0%, for HDPE, LLDPE, and PS, respectively.     

Self-Reinforced High-Density Polyethylene Prepared by Low Frequency Vibration-Assisted Injection Molding. II: Microstructure Investigation

Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD) were employed to study the microstructure of self-reinforced high-density polyethylene (HDPE) prepared by conventional injection molding (CIM) and a low frequency vibration-assisted injection molding (VAIM). SEM micrographs following permanganic etching showed the self-reinforcement of HDPE is mainly due to the existence of shish-kebab morphology within the core region for VAIM-processed HDPE samples. Pronounced molecular alignment was identified by the WAXD data. An approximate 9% increase in the crystallinity was confirmed by DSC. Both preferred molecular orientation and increased crystallinity serve to yield stronger VAIM-processed injection moldings.     

Hardening and softening during fatigue fracture

Summary The comparison of the change of hardness and plastic deformation amplitude at a constant stress loading or stress amplitude at a constant deformation loading during the fatigue process shows some singularity of the hardening and softening effects. These effects were investigated on mean carbon and low-alloyed steel and on globular cast iron.The fatigue fractures at cycle numbers 10⁴÷10⁶ under stresses below the yield strength predominate in the softening process, which arises after an inconsiderable hardness increase extends in the region to 0·2 from the fracturing cycle number. Under the stresses above the yield strength, which in some cases for annealed and coarse-grained states are below the fatigue limit, the hardening process predominates, followed by a hardness increase in the field up to 0·25 and above the fracturing cycle number.At low cycle fatigue fractures with cycle numbers < 10⁴ depending on the cyclic plastic properties of steels the fatigue process can be followed by a continuous hardening or softening till fracture. This process is characterized by the change of the deformation amplitude and a one-sided accumulation of plastic deformations at a constant amplitude of active stresses. The one-sided accumulation of deformations commonly ends in a quasistatic failure. Under loading with a constant deformation amplitude during softening a fatigue fracture takes place as a result of damage accumulation under the alternating stresses with amplitudes decreasing with cycle number.     

Long distance real-time measurement of multi-points micro-vibration in region by digital holography

Many applications require micro-vibration measurement, especially multi-points detection at long distance in real-time. In this paper, a micro-vibration measurement approach based on digital holographic interferometry is proposed for middle-low frequency detection. It can be used to monitor irregular frequency/amplitude vibration in selected region over 10 m away simultaneously and synchronously. A series of experiments were conducted including real-time measurement of 300 Hz, 1 kHz, 2 kHz and 3 kHz constant frequency/amplitude periodic vibration, precision and frequency response tests with calibration of LDV, 1 kHz irregular amplitude vibration, irregular frequency/amplitude vibration as well as the real-time measurement and simultaneous display of multi-points vibration. The experimental results demonstrate the feasibility of the proposed method and reveal its unique advantages.     

High pressure investigations of melamine

We have performed mid- and far-infrared (IR), Raman, and angular dispersive X-ray diffraction studies on melamine at high pressure up to 36 GPa. We have confirmed the presence of three phase transitions; the first between 1 and 2 GPa, the second between 7 and 9 GPa, and the third near 16 GPa. We observed a softening of the N–H symmetric and antisymmetric vibrations with pressure, suggesting that intermolecular hydrogen bonding increases as the intermolecular distance decreases similarly to what was observed in triamino-trinitrobenzene. The molecular decompression data from core intramolecular peaks of mid-IR and Raman indicate that melamine did not chemically decompose up to the highest investigated pressures but the sample suffered some irreversible amorphization. We have further clarified the lack of observation of any phase transitions in prior Raman and IR studies by examining the pressure dependence of other uninvestigated modes of vibration.     

On the frequency content of the surface vibration of a diesel engine

The results of an experimental investigation into the narrow band frequency content of the surface vibration of a particular four cylinder, water-cooled, indirect injection diesel engine are described. The long term objective, of which the work reported here is a part, is the reduction of noise emission at source. Noise is radiated from the engine as a result of surface vibration. The characteristics of surface vibration are described and an explanation is given of why the discrete frequency response of the engine has hitherto appeared to be broad band nature. The relationship of the pure tone response to the combustion pressure spectrum is also described. The vibration of the engine side wall has the greatest amplitude in the frequency band 2·9-3·8 kHz, irrespective of engine speed and load, which could be a result of piston slap. The vibration of the crankcase skirt, in contrast, is more or less uniform throughout the frequency range 0–5 kHz, reflecting the great difficulty in achieving a significant reduction in the overall level at this location. The low frequency pressure spectrum is shown to have roughly a 47 dB/decade decline in amplitude with frequency below 800 Hz, in comparison with an oft-quoted figure of 30 dB/decade. Significant differences between no load and half load pressure spectra are shown to exist.     

Ta-10W合金压缩力学性能实验研究

利用MTS材料试验机和分离式Hopkinson压杆(SHPB)实验装置对非退火状态Ta-10W合金进行了准静态和动态压缩实验,给出了材料的静态压缩屈服强度和应变率在700~3 100 s-1范围内的动态压缩应力-应变曲线,并获得了不同应变率下材料的动态屈服强度。通过对实验结果的分析可以发现,非退火状态Ta-10W合金具有较好的韧性,在所进行的实验中试件表面均未出现可见裂纹;试件材料具有较高的静、动态屈服强度,静态屈服强度达到930 MPa,动态屈服强度在1 GPa以上,在所进行的700~3 100 s-1应变率范围内,材料的动态屈服强度随应变率的增加略有提高。     

Effect of Different Local Vibration Frequencies on the Multiscale Regularity of Plantar Skin Blood Flow

Local vibration has shown promise in improving skin blood flow (SBF). However, there is no consensus on the selection of the best vibration frequency. An important reason may be that previous studies utilized time- and frequency-domain parameters to characterize vibration-induced SBF responses. These parameters are unable to characterize the structural features of the SBF response to local vibrations, thus contributing to the inconsistent findings seen in vibration research. The objective of this study was to provide evidence that nonlinear dynamics of SBF responses would be an important aspect for assessing the effect of local vibration on SBF. Local vibrations at 100 Hz, 35 Hz, and 0 Hz (sham vibration) with an amplitude of 1 mm were randomly applied to the right first metatarsal head of 12 healthy participants for 10 min. SBF at the same site was measured for 10 min before and after local vibration. The degree of regularity of SBF was quantified using a multiscale sample entropy algorithm. The results showed that 100 Hz vibration significantly increased multiscale regularity of SBF but 35 Hz and 0 Hz (sham vibration) did not. The significant increase of regularity of SBF after 100 Hz vibration was mainly attributed to increased regularity of SBF oscillations within the frequency interval at 0.0095–0.15 Hz. These findings support the use of multiscale regularity to assess effectiveness of local vibration on improving skin blood flow.     

外场作用下聚合物滞后生热效应

为了研究振动参数对聚合物黏弹性能及塑化成型过程的影响,深入分析了振动场的作用机理,揭示了相位角与滞后生热率之间的关系,得出了振动场作用下聚合物塑化成型速率表达式,最后通过聚对苯二甲酸乙二醇酯(PET)动态毛细管挤出以及多维振动塑化成型设备进行实例计算和实验研究,实验结果和理论计算值符合得很好,并得出结论: PET塑化速率随振动频率的增加呈先增加后减小的趋势,当激振频率趋向于材料固有频率时(振动频率约为15 Hz时),PET塑化速率达到最大值,当振幅为6 MPa时,其值约为22 g/min,为相同振幅下,频 关键词： 振动场 滞后生热 相位角 低温成型     

Fabrication of Poly-l-lactide Biomaterials with High Mechanical Properties Using Fiber Oriented Pressing

A new technique of dilute solution spinning to obtain poly-l-lactide (PLLA) fiber was presented. PLLA materials were fabricated by using fiber oriented pressing and the effects of pressing pressure and temperature on the mechanical properties and weight average molecular mass of PLLA were investigated. Good oriented fibers with porous structure (0.1 ～ 1 μm) were obtained by a dilute solution spinning method. Bending and shearing strength of PLLA samples first increase and then decrease with the increase of pressing temperature and pressure. The bending strength, shearing strength, and bending modulus reach 238.8 ± 6.5 MPa, 127.5 ± 3.5 MPa and 3.25 ± 0.25 GPa, respectively, if the pressing temperature is 185°C and the pressure is 130 MPa. These values are greater than conventional pressing methods. In addition, the decrease in weight average molecular mass (19.5%) that results from using oriented pressing is lower than that seen (30.0%) by using the conventional pressing method.     

常温0～1GPa压力下重晶石的拉曼光谱研究

利用碳化硅压腔装置研究了高压下重晶石的S-O对称伸缩振动v987和对称弯曲振动v452及v462的拉曼光谱变化特征.实验结果表明:在常温和0～1GPa压力范围内重晶石稳定,其拉曼谱峰随压力升高向高波数方向移动,二者的关系表达式分别为:v987=0.004 4p+987.42,v452=0.002 3p+452.6,v462=0.001 8p+462.42,而且伸缩振动受压力的影响比弯曲振动大.重晶石的987 cm-1拉曼谱峰强度约为石英464 cm-1拉曼谱峰的六倍,可作为压腔中良好的压力标定物.实验得到压力与重晶石987 cm-1峰偏移量的关系为:p(MPa)=223.16×(△vp)987-90.35(987 cm-1相似文献   

Mechanical properties of kaolinite ‘macro-crystals’

The mechanical properties of a rare sample of kaolinite macroscopic crystals were evaluated using instrumented indentation. The crystals were also characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy before and after heat treatment at 1100°C. The results are explained in terms of the fracture process occurring in the layered structure of kaolinite, and of the effect of roughness on the hardness and elastic modulus. Data analysis using One-way ANOVA (p?<?0.05) showed that the values of hardness and elastic modulus obtained are statistically homogeneous. Before heat treatment, the sample was composed essentially of kaolinite, with hardness of 42?MPa and elastic modulus equal to 1.3?GPa. After calcination at 1100°C, the sample keeps its layered habit and consists of amorphous metakaolinite. The hardness increases to 360?MPa and the elastic modulus increases to 6.9?GPa.