Dynamic mechanical properties of isotactic PMMA

The aim of this paper is a comparison of the dynamic mechanical behaviour of amorphous and partially crystallised isotactic PMMA. Parameters are proposed that affect the different relaxations that appear in the dynamic mechanical isochronal spectra. It has been found that the temperature of the maximum of the loss tangent, as well as the activation energy, is higher for the totally amorphous polymer. The beta-relaxation appears clearly in the case of the completely amorphous polymer, with an activation energy of 105kJ/mol; this relaxation cannot be found for the semicrystalline polymer.     

Dynamic mechanical properties of very thin adhesive joints

The effective mechanical properties of a polyurethane adhesive (oligoetherdiol, ‐triol, MDI) in gold joints (bond line thickness, d_P = 35–550 µm) are studied in the linear deformation range by dynamic mechanical analysis in shear mode. These properties depend on d_P: thin ones possess a higher dynamic glass transition temperature and show a narrower glass transition than the thick ones. The storage modulus rises with decreasing d_P for the rubbery plateau. The results attest mechanical interphases in the polyurethane with increased crosslink density and reduced cooperative mobility than in bulk. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42058.     

不同应变率时复合材料胶接结构力学性能试验研究进展

介绍了在不同应变率时对材料性能及结构的表征方法和相关设备,综述了胶粘剂、复合材料和复合胶接材料在不同应变率时的力学性能研究,特别对中高应变率时材料的胶接性能进行了探讨。最后提出了若干进一步需要研究解决的问题。     

Experimental results on the correlation between cross-linking,polarization and space charge in PMMA

The influence of cross-linking upon polarization and space charge is investigated. PMMA samples of different cross-linking degrees were prepared. The samples were poled under several DC fields and temperatures. Space-charge measurements were made by the thermal-step method. The ‘cleaning’ technique was used to separate dipolar phenomena and injected charge. The results show that cross-linking affects the state of polarization of the samples and could favour space-charge accumulation. © 1999 Society of Chemical Industry.     

Adhesive joints with improved mechanical properties for aerospace applications

Adhesion is attracting increasing interest in the aerospace field since composite materials have become, together with aluminium alloys, the main structural materials for aircraft primary structures. Nano-graphite was demonstrated to improve the mechanical performance of several polymers used as composite matrices. In this work Single Lap Joints (SLJs) of unidirectional composite laminates were manufactured, tested and simulated: two families of specimens were investigated and compared, one joined using conventional epoxy resin, the other joined with an adhesive obtained mixing the same epoxy resin with nano-graphite particles. The dispersion of expanded and sonicated graphene stacks (EGS, 3% wt) in the epoxy matrix was obtained by the swelling method, dispersing first the filler in acetone and then mixing it with the epoxy oligomers. Finally the solvent was evaporated and the filler-epoxy mixture was degassed under vacuum before adding an amine curing agent in a stoichiometric quantity. The research demonstrates the superior mechanical properties of the adhesive with the addition of nano-graphite through experimental characterization of its behaviour in terms of strength and energy absorption. Finite element numerical simulations have been carried out using the Cohesive Zone Model (CZM) element, obtaining as parameters the maximum shear stress and the critical fracture energy for the two adhesives. A good correlation between numerical and experimental results has been achieved and the criteria for developing reliable and accurate non-linear models of the adhesive failure have been established.     

Microstructure and mechanical properties of SiC-SiC joints joined by spark plasma sintering

The development of reliable joining technology is of great importance for the full use of SiC. Ti₃SiC₂, which is used as a filler material for SiC joining, can meet the demands of neutron environment applications and can alleviate residual stress during the joining process. In this work, SiC was joined using different powders (Ti₃SiC₂ and 3Ti/1.2Si/2C/0.2Al) as filler materials and spark plasma sintering (SPS). The influence of the joining temperature on the flexural strength of the SiC joints at room temperature and at high temperatures was investigated. Based on X-ray diffraction and scanning electron microscopy analyses, SiC joints with 3Ti/1.2Si/2C/0.2Al powder as the filler material possess high flexural strengths of 133 MPa and 119 MPa at room temperature and at 1200 °C, respectively. The superior flexural strength of the SiC joint at 1200 °C is attributed to the phase transformation of TiO₂ from anatase to rutile.     

横纹槽换热管力学性能试验研究

通过试验研究了横纹槽换热管的力学性能,验证了这种结构的可靠性并获得了几点重要结论。     

Comparison of the thermo‐mechanical properties of chemically synthesized PMMA and PTEGDMA polymer

The acrylic monomeric couple, methyl methacrylate (MMA)‐triethylene glycol dimethacrylate (TEGDMA) was mixed and polymerized through bulk polymerization in open test tubes using three different routes. The simplest one was a monomer mixture of 70 wt % of MMA and 30 wt % of TEGDMA. The polymerization reaction was initiated by benzoil peroxide (BPO). The second route used a casting syrup composed of 20 wt % polymethyl methacrylate (PMMA) dissolved in 80 wt % MMA. This casting syrup was mixed with 30 wt % TEGDMA to initiate the polymerization with BPO. The final synthesis route was carried out using the aforementioned chemical composition with a polymerization initiated with a mixture of BPO and N,N dimethyl p‐toluidine (DMT) at a ratio of 10 : 1. The three synthesis routes produced different types of polymers which have remarkable differences in morphology, thermal behavior, and tensile properties. Several thermal transitions were found in each type of polymer by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Gas chromatography and Fourier transform infrared were employed to determine the cause of each thermal transition revealed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A mechanical analysis of the physical bonding properties of soft lining materials to PMMA

The bonding properties of soft liners to acrylic denture bases are characterized by their variable resistance to external loading. This resistance depends on the nature of the load, the chemistry and mode of polymerization of the liner, and the topography of the acrylic surface to which the liner is applied. The results obtained indicate that heat-curing acrylic soft liners are superior to silicone rubber materials; and that light smoothing of the acrylic surface prior to processing the liner has a beneficial effect on bonding.     

Effects of salt spray on the mechanical properties of aluminum-epoxy adhesive joints

The aluminum bonding joints were aged in salt spray fog for various aging time from 0 to 1200?h. Uniaxial tensile tests were conducted for the joints to obtain the residual strength of the joints. The test results showed that the residual strength of the joints increases firstly and then decreases with the aging time in salt spray environment. The mechanism of the spray fog environment effect on the joint residual strength is analyzed by infrared spectral analysis and energy dispersive spectroscopy experiments. It is suggested the effect of aging time in the salt spray fog on the joint residual strength is the competing result of two mechanisms. One positive mechanism is that the adhesive expands after absorbing water in the early aging and reaches its saturation after a certain time, which leads to releasing of the internal stress in joints and consequently increases the joint residual strength. Another negative mechanism is that the water molecules permeating into the adhesive when aged in salt spray fog leads to the plasticization of the adhesive, which results in decreasing the joint residual strength as the aging time increases.     

Electrical and mechanical properties of multi‐walled carbon nanotubes reinforced PMMA and PS composites

The use of multi‐walled carbon nanotubes (MWCNT) as reinforcing material for thermoplastic polymer matrices, polymethyl methacrylate (PMMA), and polystyrene (PS) has been studied. MWCNT were synthesized by chemical vapor deposition (CVD) technique using ferrocene‐toluene mixture. As‐prepared nanotubes were ultrasonically dispersed in toluene and subsequently dispersed in PMMA and PS. Thin polymer composite films were fabricated by solvent casting. The effect of nanotube content on the electrical and mechanical properties of the nanocomposites was investigated. An improvement in electrical conductivity from insulating to conducting with increasing MWCNT content was observed. The carbon nanotube network showed a classical percolating network behavior with a low percolation threshold. Electromagnetic interference (EMI) shielding effectiveness value of about 18 dB was obtained in the frequency range 8.0–12 GHz (X‐band), for a 10 vol% CNT loading. An improved composite fabrication process using casting followed by compression molding and use of functionalized MWCNT resulted in increased composites strength. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Physical,mechanical, and thermal properties of PVC/PMMA blends in relation to their morphologies

The effect of blending poly (methyl methacrylate) (PMMA) in various proportions with suitably stabilized and plasticized poly (vinyl chloride) (PVC) was studied with reference to their physical, mechanical, and thermal properties. The resulting morphologies of the various blends were also studied to find a suitable explanation of these properties. The physical and mechanical properties of such polyblends revealed a substantial increase in toughness accompanied with unusual increase in modulus and ultimate tensile strength after an initial drop at the initial stages of PMMA incorporation compared to pure reference compound PVC. The toughening effect, however, undergoes a reduction with increasing proportion of PMMA but it never goes below that of pure PVC (reference compound) within the ranges of PMMA incorporation under study. The various polyblends exhibit the two‐stage degradation typical of PVC and all of them possess higher thermal stability as manifested in their characteristic thermograms. The softening characteristics imparted by PMMA were also reflected in their respective TMA curves. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2721–2730, 2004     

介孔SBA-15有机化修饰对PMMA杂化材料力学性能的影响

采用硅烷偶联剂对SBA-15进行了有机化修饰(即:SBA-15-G),利用在位分散聚合法制备了SBA-15/PMMA和SBA-15-G/PMMA杂化材料,研究了SBA-15和SBA-15-G在PMMA基体中的介观有序性和分散性以及对杂化材料的力学性能的影响规律。结果表明有机化修饰使SBA-15孔容、孔径和比表面积减小,表面亲油性提高;SBA-15和SBA-15-G在基体中仍保持长程有序结构;有机化修饰改善了SBA-15在基体中的分散性和与基体的界面结合,显著增强了杂化材料的力学性能。当SBA-15-G为4%时,杂化材料的拉伸强度和模量分别提高了45%和40.4%,当SBA-15-G为2%时冲击强度达到最大,比基体提高了36.6%。,     

The effect of transcrystallinity on the transverse mechanical properties of single-polymer polyethylene composites

The microstructure of polyethylene (PE)/PE composites, consisting of the high-density PE (HDPE) matrix and ultrahigh molecular-weight PE (UHMWPE) fibers, was investigated. Single-fiber composites were prepared and analyzed in a hot-stage crystallization unit attached to a polarizing microscope, aiming to find out how the conditions of crystallization affected the transcrystallinity (tc) growth at the fiber-matrix interface. Thermal treatments leading to two extreme microstructures, of either maximum or minimum thickness of the transcrystalline zone, were sought. It was found that a uniform transcrystalline layer was developed on the UHMWPE fiber from the HDPE melt under isothermal conditions, whereas rapid cooling from the melt prevented the generation of tc. The mechanical properties of unidirectional composite laminae either with or without the transcrystalline zone were measured. A comparison of the transverse strength predicted by theoretical models with the experimental values revealed good interfacial adhesion in the PE/PE system. It was shown that the tc growth had a negligible effect on the composite mechanical properties in the longitudinal direction, whereas it resulted in a 50% decrease of the transverse tensile strength and strain to failure. Scanning electron microscopy attributed that observation to premature brittle failure at tc/tc contact regions. © 1995 John Wiley & Sons, Inc.     

Enhanced mechanical and thermal properties of PS/mica and PMMA/mica nanocomposites by emulsion polymerization

Polymer/mica nanocomposites of styrene or methyl methacrylate have been prepared by emulsion polymerization. For the polymer/mica nanocomposites, the mica was dispersed individually in water, and we found that they were adsorbed on the surface of monomer droplets. Polymer/mica nanocomposites were obtained by adding an aqueous dispersion of layered silicate into the polymer emulsion. X‐ray diffraction (XRD) and FTIR spectra were used to characterize the structures of the nanocomposites. The degree of dispersion of these nanocomposites were investigated by using a transmission electron microscopy (TEM). Furthermore, the thermal and mechanical properties of polymer/mica nanocomposites were determined by using thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and dynamic mechanical analysis (DMA). The increased tan δ of the obtained nanocomposites is ascribed to the fine dispersion of mica particles into the polymer matrix. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Identification of mechanical properties of CuSil-steel brazed structures joints: a numerical approach

In this paper, the inverse method is used to identify the mechanical characteristics of a brazed joint. This technique is based upon tensile tests and/or shearing test combined with the results of a calculation using finite elements method. This paper shows that calculation of a brazed assembly under an elastic behavior assumption is flawed. A correct study of a brazed assembly must be done under an elastoplastic assumption. The presented method will be used for calculation of molds manufactured by stratoconception (sheet metal assembling).     

Biological properties of PMMA/nHAp and PMMA/3-APT-nHAp nanocomposites

In this study, nanocomposite-implant materials with the filler materials, which are nanohydroxyapatite (nHAp) and nHAp modified by [3-(2-aminoethilamino)propyl]trimethoxysilane, using poly(methylmethacrylate) as a matrix according to the melting method, were synthesized. The nanocomposites were characterized using X-ray diffraction, Fourier transform infrared spectroscopy–attenuated total reflectance, scanning electron microscopy, transmission electron microscopy, differential thermal analysis/thermogravimetric analysis, and differential scanning calorimetry devices. Experimental results showed that the thermal stability of nanocomposites increased, and they were hemocompatible, had no negative effect on antioxidant enzymes, and had antibacterial activity.     

Dynamic mechanical properties and correlation with dynamic fragility of sisal reinforced composites

In this study, the reinforcement effect in sisal/polyester composites containing distinct reinforcement content was studied ranging from fragile to strong classification. The results indicate that the reduced storage modulus changes steadily, and the loss modulus and the tan δ peak are broader for composites containing more fiber (dynamically strong composites). As more fiber was incorporated in the resin, lower peak height for the tan delta curve was obtained, which may be indicative of lower energy dissipation due to a greater relative amount of interface. Also, the use of reduced dynamic mechanical curves (similar to dynamic fragility) is an alternative to facilitate the study of the material behavior. POLYM. COMPOS., 36:161–166, 2015. © 2014 Society of Plastics Engineers     

Impact strength and dynamic mechanical properties correlation in elastomer‐modified polypropylene

This article describes the impact and dynamic mechanical properties of rubber‐modified binary blends of polypropylene (PP). Two conventional elastomers [viz. ethylene vinyl acetate copolymer (EVA) and ethylene propylene diene terpolymer (EPDM)] were used as an impact modifier for PP. It is clearly indicated by the results that EPDM is better than EVA as an impact modifier of PP. Analysis of data of dynamic mechanical properties and impact properties at various compositions of the blends revealed a direct correlation between impact properties and dynamic mechanical loss tangent. The energy dissipation due to viscoelastic relaxation is therefore suggested as a mechanism of impact toughening of PP, in addition to the other commonly known mechanisms of toughening (viz. shear yielding and crazing induced by deformation of rubber‐phase domains). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 962–971, 2000     

Characterisation of the transverse mechanical properties of carbon/carbon composites by spherical indentation

The mechanical characterisation of the carbon/carbon composite in the transverse direction is essential for the design of braking discs. This paper presents a technique based on spherical indentation to identify the mechanical behaviour of such materials in the transverse direction.After the presentation of the material properties as determined from static and fatigue compression tests, the indentation technique is described in detail. The characterisation technique used takes into consideration the transverse isotropy of these materials. The method used allows to identify the material behaviour in elastic and inelastic fields. Characterisation of elastic parameters is carried out after identification of the Hertz law in the unloading indentation cycles. The hardening parameters and the elastic limit are identified by expressing the law of Hertz in strain/stress form.The identified parameters are used in a simulation of an indentation test by finite element method. A good agreement is found between numerical and experimental results.