A DYNAMIC MECHANICAL ANALYSIS STUDY OF THE TRANSITION BEHAVIOUR OF I-PP/EPDM BLENDS

The transition behaviour of the blends of isotactic polypropylene (i-PP) with ethylene-propylene terpolymer (EPDM) containing 42 wt% propylene was investigated by dynamic mechanical analysis technique (DMA). Owing to its high propylene content, EPDM is compatible with i-PP to some degree. The interaction between the two components was strengthened. As expected, for partially compatible system the glass transition temperature of i-PP in the blends shifted to lower temperature. It was found that there existed two transitions, αEPDM and βEPDM, for the EPDM used in this work. The former was considered to be the glass transition of the random chain segments of EPDM, while the latter the local motion of the long ethylene sequences in EPDM. The unusual transition behaviour of αEPDM in the blends was explained in terms of the greater thermal expansion of EPDM and the compatibility of the two components. On the other hand, the βEPDM changed with the composition of the blends in a regular manner.

Importance of Dynamic Mechanical Analysis to Predict Performance of the Polyvinyl Acetate Wood Adhesives in Summer Season

Conventionally available Polyvinyl acetate (PVAc) wood glues are polyvinyl alcohol (PVA) stabilized, with drawbacks like poor strength at high humidity, poor strength at high temperature and workability at low-temperature. PVAc is non-resistant to high humidity, and if such adhesive bonds are exploited in a highly humid environment, its strength substantially decreases. Sufficiently water-resistant adhesive bonds are achieved by modifying PVAc dispersion with special chemicals like acrylic acid (AA) and N-methylol acrylamide (NMA) as a co-monomer, Silanes, and ethylene modified PVA. The Lewis acids like aluminium chloride and aluminium nitrate are used as cross-linkers. So PVAc adhesives are classified as reactive and non-reactive glue. Application of non-reactive D1 (as per EN 204-205) and reactive D2 and D3 (as per EN 204-205) adhesives for bonding laminate on plywood is a regular practice in the Indian market. In summer time, Crack formation was seen in laminate bonded with reactive D2 and D3 adhesives in regions where the room temperature was above 45°C. However, if the same laminate substrates were bonded with non-reactive D1, no cracks were seen. To analyse the above phenomenon, we have done Dynamic mechanical analysis of non-reactive D1, reactive D2 and D3 adhesive.

Analysis and Inverse Substructuring Computation on Dynamic Quality of Mechanical Assembly

Mechanical assembly has its own dynamic quality directly affecting the dynamic quality of whole product and should be considered in quality inspection and estimation of mechanical assembly. Based on functional relations between dynamic characteristics involved in mechanical assembly, the effects of assembling process on dynamic characteristics of substructural components of an assembly system are investigated by substructuring analysis. Assembly-coupling dynamic stiffness is clarified as the dominant factor of the effects and can be used as a quantitative measure of assembly dynamic quality. Two computational schemes using frequency response functions（FRFs） to determine the stiffness are provided and discussed by inverse substructuring analysis, including their applicable conditions and implementation procedure in application. Eigenvalue analysis on matrix-ratios of FRFs before and after assembling is employed and well validates the analytical outcomes and the schemes via both a lumped-parameter model and its analogic experimental counterpart. Applying the two schemes to inspect the dynamic quality provides the message of dynamic performance of the assembly system, and therefore improves conventional quality inspection and estimation of mechanical assembly in completeness.

DYNAMIC MECHANICAL RESPONSE OF CRAZES IN POLYSTYRENE

Dynamic mechanical analysis was used to study the mechanical properties and microstructureof crazes in polystyrene produced in air or in methanol at different temperatures. A new loss peakwas found at about 82℃,which is assigned to glass transition peak of craze fibrils. The decreaseof glass transition temperature of polymer in craze fibrils is due to the high values of surface tovolume ratio. The glass transition temperature ratio of craze fibrils to bulk material （T;/Tg） hasbeen expressed as a function of the fibrils diameter （d）. From T;of craze fibrils,the value of fibrildiameter can be calculated. Annealing the crazed specimen at room temperature makes the fibrilsplastically deform and cause the fibrils to thin slightly,whereas annealing the crazed specimen atthe temperature near T;of the craze fibrils makes the fibrils bundle together.

Crystallization and Dynamic Mechanical Behavior of Coir Fiber Reinforced Poly(Butylene Succinate)Biocomposites

The crystallization behavior,crystal morphology and form,and viscoelastic behavior of poly(butylene succinate)(PBS)and coir fiber/PBS composites(CPB)were investigated by differential scanning calorimetry(DSC),polarized optical microscopy(POM),X-ray diffraction(XRD)and dynamic mechanical analysis(DMA).The results of DSC measurement show that the crystallization temperature increases with the filling of coir fibers.POM images reveal that the spherulitic size and crystallization behavior of PBS are influenced by the coir fibers in the composites.XRD curves show that the crystal form of pure PBS and CPB are remaining almost identical.In addition,the storage modulus of CPB significantly increases comparing with the pure PBS.This predicted the dimensional stability and improved load-deformation temperature.In conclusion,the addition of coir fibers has a significant effect on the thermal properties of the matrix.

The Effects of Stacking Sequence on Dynamic Mechanical Properties and Thermal Degradation of Kenaf/Jute Hybrid Composites

This research focused on the dynamic mechanical and thermal properties of woven mat jute/kenaf/jute(J/K/J)and kenaf/jute/kenaf(K/J/K)hybrid composites.Dynamic mechanical analysis(DMA)and Thermo-gravimetric Analysis(TGA)were used to study the effect of layering sequence on the thermal properties of kenaf/jute hybrid composites.The DMA results;it was found that the differences in the stacking sequence between the kenaf/jute composites do not affect their storage modulus,loss modulus and damping factor.From the TGA and DMA results,it has been shown that stacking sequence has given positive effect to the kenaf/jute hybrid composite compared to pure epoxy composite.This is because kenaf and jute fibre has increased the Tg values of the composites,thus affect the thermal degradation.Results showed that the storage modulus for kenaf/jute hybrid composites increased compared with pure epoxy composites with increasing temperature and the values of remained almost the same at glass transition temperature(Tg),the hybrid composite perhaps due to the improved fibre/matrix interface bonding.The preliminary analysis could provide a new direction for the creation of a novel hybrid composite which offers unique properties which cannot be accomplished in a single material system.

Temperature Dependency of Dynamic Mechanical Properties of Cement Asphalt Paste by DMTA Method

We investigated the temperature dependency of the dynamic mechanical properties of cement asphalt paste by the dynamic mechanical thermal analysis（DMTA） method. The experimental results show that the dynamic mechanical properties of cement asphalt pastes are sensitive to temperature due to the inclusion of asphalt, and may go through different states within a temperature range of-40 ℃ to 60 ℃, which is different from that of pure cement and asphalt. As the temperature of the cement asphalt paste increases, a considerable change of dynamic mechanical properties, including storage modulus（E＇）, loss modulus（E＇＇） and loss factor（tand） is observed. Moreover, the influence of asphalt to cement（A/C） ratio on the temperature sensitivity of the dynamic mechanical properties of cement asphalt composites was investigated. The temperature dependency of cement asphalt composites is ascribed to the temperature dependency of the asphalt and its interaction with cement paste. A simple fractional model is proposed to describe the viscoelastic behavior of cement asphalt composites.

Dynamic Mechanical and Thermal Properties of Cross-linked Polystyrene/Glass Fiber Composites

Cross-linked polystyrene/glass fiber composites were fabricated using cross-linked polystyrene （CLPS） as matrix and E-glass fiber as the reinforcement. Surfaces of E-glass fibers were modified by vinyl triethoxysilane （VTES）, vinyl trimethoxysilane （VTMS） and γ-methacryloylpropyl trimethoxysilane （MPS）. The treated glass fibers were analyzed by fourier transform infrared spectroscopy （FTIR）. Dynamic mechanical thermal analysis （DMTA） and thermo-gravimetric analysis （TGA） were employed to investigate the effect of glass fibers surface modification on viscoelastic behavior and thermal properties. The morphology of fracture surfaces of various composites was observed by scanning electron microscopy （SEM）. The results revealed that these coupling agents were connected to the surfaces of the fibers by chemical bonding. Dynamic mechanical properties as well as thermal stability of the composites were improved considerablely, but to varying degrees depending on the fiber modification. The diversities of improvement of properties were attributed to the different interfacial adhesion between CLPS matrix and the glass fibers.

Dynamics analysis on transverse cutting mechanism of straw checkerboard paving robot

The transverse cutting mechanism of the checkerboard paving robot, which directly affects the robot＇s operation, is regarded as the most important part in a transverse pavement system This research aims at designing a new system which is appropriate for desert wofidng en- vironments and finishing cutting the rope of straw. In this paper, computer emulating technology is applied, and with three-dimensional modeling by Pro/ENGINEER software, can observe whether or not interference exists. Also, the speed and displacement parameters of the main parts of the cutting system are given by the dynamic emulation by Automatic Dynamic Analysis of Mechanical System （ADAMS）, which theoretically assures the feasibility and appropriateness of the cutting mechanisrn~ Finally, results of the experinaent shows that the cutting mechanism can cut the straw strand as designed.

Theoretical analysis of thermoviscoelastic contact between friction lining and wire rope in mine friction hoists

Serious accidents of mine hoists caused by high-speed sliding between friction lining and wire rope are often seen in coal mines.In order to solve this problem,we analyzed the contact characteristics between friction lining and wire rope.Then we carried out a dynamic mechanical analysis(DMA) to explain the change in mechanical properties of the friction lining as function of temperature and load frequency and found that temperature has a stronger effect on the mechanical properties than the frequency.We used multiple regression analysis to obtain the thermoviscoelastic constitutive relations of the friction lining.As well we derived the analytic solution for the thermoviscoelastic contact radius and pressure by combining the theory of viscoelastic contact mechanics with thermoviscoelastic constitutive relations.

SiC nanowire-based SU-8 with enhanced mechanical properties for MEMS structural layer design

In addition to being used for pattern transfer,the negative photoresist SU-8 iswidely used as a structural material in microelectromechanical systems(MEMS).Due to its good photopatternability,SU-8 has lower manufacturing costs than many other materials,but its mechanical properties are relatively weak to some extent,which limits its performance.The mechanical properties of epoxy-like SU-8 can be enhanced by addingmicro-or nano-fillers such as carbon nanotube,clay,and SiC nanowire,which have superior elastic modulus.In this study,SiC nanowires were used to improve the mechanical properties of SU-8 while the SU-8 retains its photopatternability.The SiC nanowires were uniformly dispersed in SU-8 by stirring and ultrasonication.SU-8 materials with different SiC nanowire contents were fabricated into dog bone samples by lithography.The elastic modulus,storage modulus,and damping factor of the samples were measured by the Dynamic mechanical analysis(DMA)Q800.The experiment result shows that the rigidity and toughness increased,and the damping reduced.The 2 wt%SiC nanowires-reinforced SU-8 had a 73.88%increase in elastic modulus and a 103.4%increase in elongation at break.Furthermore,a spring component made by SiC-doped SU-8 could withstand greater acceleration.The SiC nanowires-reinforced SU-8 has the potential tomeet higher requirements in the design andmanufacture of MEMS and greatly reduce the manufacturing costs of MEMS devices.

INTEGRAL INVARIANTS OF A HOLONOMIC DYNAMICAL STSTEM

This paper uses Poincare’s formalism to study . the integral invariants of aconservative holonomic dynamical system Introducing new parameters for theasynchronous variation, a generalization of the poincare and Poincare-Cartan integralinvariants is presented.

滚-跳多运动模式球形机器人的动力学仿真研究

复杂的探索环境对探测机器人的通行能力提出了更高要求,具有多种运动模式的球形机器人是探测机器人领域的研究热点之一。通过对球形机器人内部构件质量分布的调节,设计了一种基于单摆驱动式的滚-跳多运动模式球形机器人,其具有滚动、转向、爬坡与跳跃4种基本运动能力;随后,又根据球形机器人的设计方案建立了球形机器人4种基本运动动力学方程。利用Automatic Dynamics Analysis of Mechanical Systems(ADAMS)软件构建该球形机器人虚拟样机并对其进行了滚动、转向、爬坡与跳跃的动力学仿真,最后以此为依据计算滚动、转向、爬坡与跳跃运动性能的仿真值,并制作实验室样机验证了动力学仿真的正确性。

Influence of oscillation strain on the dynamic mechanical relaxation of a La-based metallic glass

Dynamic mechanical relaxation processes,particularly secondary relaxation processes,are closely related to the mechanical and physical properties of metallic glasses.Here the effect of oscillation strain amplitude on the secondary relaxation of a typical Labased metallic glass was studied using the dynamic mechanical analysis method.The apparent activation energy of theβrelaxation is shown to increase with the oscillation strain amplitude.When it changes from 0.02%to 0.16%,the activation energy increases from 0.73 to 0.96 eV.Simultaneously,the intensity of theβrelaxation shifts toward high temperature.Additionally,the apparentβrelaxation is found to be sensitive to the physical aging below the glass transition temperature.The findings suggest a correlation between the inelastic deformation and the relaxation behavior of amorphous metals.

Toughening wood/polypropylene composites with polyethylene octene elastomer (POE)

Polyethylene octene elastomer (POE) as impact modifier was incorporated into wood/polypropylene composites (WPC) to enhance the impact strength of the composite. Two extruding routes, i.e. direct extruding route and two-stage extruding route, were adopted to produce Wood Powder/PP/POE ternary composites. The mechanical and dynamic mechanical analysis (DMA) properties of the composites were investigated. The results showed that the addition of POE can increase the impact strength of the composites, and the composites produced via two-stage extruding route showed superior mechanical properties. The results of the DMA confirmed the mechanical tests.

Preliminary study of viscoelastic properties of MAPP-modified wood flour/polypropylene composites

Viscoelastic properties of maleated polypropylene （MAPP）-modified wood flour/polypropylene composites （WPC） were investigated by both a compression stress relaxation method and dynamic mechanical analyses （DMA）. Three wood to polymer ratios （40：60, 60：40, and 80：20） and five MAPP loading levels （0, 1, 2, 4 and 8%） were used to study their effects on the viscoelastic prop- erties of MAPP-WPC. The results show that： 1） higher wood to polymer ratio corresponds to higher stress relaxation levels for unmodified WPC. The modification with MAPP has an obvious effect on the stress relaxation of MAPP-WPC at higher wood to polymer ratios （60：40 and 80：20）, but almost no effect at the 40：60 wood to polymer ratio. The optimal MAPP loading level for the wood to polymer ratio of 60：40 appears at 1%; 2） the storage modulus reaches its maximum at a MAPP loading level of 1% for wood to polymer ratios of 40：60 and 60：40, while for the 80：20 wood to polymer ratio, a higher storage modulus is observed at higher MAPP loading levels, which is quite consistent with the stress relaxation results. The results suggested that a suitable loading level of MAPP has a positive effect on the viscoelastic properties of WPC at higher wood to polymer ratios. Excessive MAPP loading would have resulted in adverse effects.

Viscoelastic models revisited:characteristics and interconversion formulas for generalized Kelvin-Voigt and Maxwell models

Generalized Kelvin-Voigt and Maxwell models using Prony series are some of the most well-known models to charac­terize the behavior of polymers.The simulation software for viscoelastic materials generally implement only some material models.Therefore,for the practice of the engineer,it is very useful to have formulas that establish the equivalence between different models.Although the existence of these relationships is a well-established fact,moving from one model to another involves a relatively long process.This article presents a development of the relationships between generalized Kelvin-Voigt and Maxwell models using the aforementioned series and their respective relaxation and creep coefficients for one and two summations.The relationship between the singular points(maximums,minimums and inflexion points)is also included.

Nonlinear Mechanism of Bed Load Transport

From the group movement of the bed load within the bottom layer,details of the nonlinear dynamic characteristics of bed load movement are discussed in this paper.Whether the sediment is initiated into motion corresponds to whether the constant term in the equation is equal to zero.If constant term is zero and no dispersive force is considered,the equation represents the traditional Shields initiation curve,and if constant term is zero without the dispersive force being considered,then a new Shields curve which is much lower than the traditional one is got.The fixed point of the equation corresponds to the equilibrium sediment transport of bed load.In the mutation analysis,we have found that the inflection point is the demarcation point of breaking.In theory,the breaking point corresponds to the dividing boundary line,across which the bed form changes from flat bed to sand ripple or sand dune.Compared with the experimental data of Chatou Hydraulic Lab in France,the conclusions are verified.

Influence of Different Medium Aging on Advanced Composite T300/5405

The aging properties of advanced composite T300/5405 which soaked in 15# hydraulic oil, 4010 lubricating oil, RP-3 kerosene and AHC-1 cleaner were studied. The absorption and mechanical properties of the composites were measured, and the scanning electron microscopy （SEIVO, dynamic mechanical analysis （DMA） and the infrared analysis （IR） were used to investigate the properties＇ changes of the composite. The aging mechanism of composite T300/5405 was also discussed. The experimental results show that the absorption of the composite in AHC-1 was the biggest, and the other three mediums had little effect on the composites. The mechanical properties declined in the aging. The composites have undergone chemical change in the test; Tg rose or declined atter the aging, and the AHC-1 cleaner and 4010 lubricating oil had the greatest influence on the Tg.

Preparation, Characterization, and Comparison of Thermal Properties of Aromatic Polyether Imides

Two aromatic polyimides were prepared by two- step way. Firstly, the poly（amic acid）s were synthesized from 1, 3 - bis（4 - aminophenoxy）benzene and two different aromatic dianhydrides. Secondly, polyimides were prepared via thermal imidization of poly（amic acid） precursors. The polyimides prepared were insoluble in common organic solvents such as tetrahydrofuran, chloroform and N, N- dimethyiformamide. The inherent viscosities of poly（amic acid）s were 1.82 dL/g and 2.67 dL/g. The high inherent viscosities were due to the strong intra- or intermolecular hydrogen interaction. The polyimides were characterized by mechanical and thermal analysis. It was found that the samples are of excellent thermal stability, higher glass-transition temperature and excellent dynamic mechanical and thermal properties.