degradation dynamic mechanical analysis

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Dynamic Reliability Analysis of Mechanical Components Based on Equivalent Strength Degradation Paths

Dynamic Reliability Analysis of Mechanical Components Based on Equivalent Strength Degradation Paths

To overcome the shortcomings of conventional LSI models, reliability models based on stochastic process theory are investigated in which load and strength are modelled as two stochastic processes. Lewis [5] analysed the time-dependent behaviour of a 1-out-of-2: G redundant system by combining the LSI model with a Markov model. Geidl and Saunders[6] introduced time-dependent elements into the reliability equation to estimate the reliability. Somasundaram and Dhas[7] put forward a generalized formula to estimate the reliability of a dynamic parallel system, in which components equally shared the load. Noortwijk and Weide [8] developed a reliability model, in which load and strength are described as two stochastic processes. Labeau et al. proposed the framework of a dynamic reliability platform and identified its main constituents [9]. Zhang et al. analysed the main methods for dynamic reliability estimation of nuclear power plants, which include discrete dynamic event trees and Monte Carlo simulation [10]. Slak analysed production planning and scheduling, cutting tools and material flow process, and manufacturing capacities [11]. Barkallah et al. proposed a method for process planning to determine the tolerance for manufacturing with statistical tools [12].
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Tannin Ca Complex as Green Thermal Stabilizer Additive for PVC: Viscoelastic Properties

Tannin Ca Complex as Green Thermal Stabilizer Additive for PVC: Viscoelastic Properties

This result clearly indicate that thermo-plastic properties of PVC influenced by the presence of tannin deriva- tive which works to prevent or reduce the thermal degradation and undesirable changes in the chemical structure of polymer during thermal mixing and thermal compression molding courses such as cross linking reactions. One of the main reasons for increased the Tg values (or Tg range) in a polymer, is the crosslinking reactions. These reactions restrict the movement of polymer segments and lead to rapid increasing in the molecular weight of polymer which will result in an increase of the Tg or to Tg appears at higher temperatures ranges. Based on the DMTA analysis results, the presence of tannin derivative actually reduce the formation of conjugated double bonds which are a result to dehydrochlorinations reactions of PVC and then prevent the crosslinking reaction during mixing or formulations process. In particular, the improvement of dynamic mechanical properties of PVC by tannin derivative can be explained in term of do not restricted the thermal motions and transitions of PVC chains such as Tg and flow transitions.
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Mechanical, thermal and dynamic mechanical analysis of jute fibre reinforced epoxy composite

Mechanical, thermal and dynamic mechanical analysis of jute fibre reinforced epoxy composite

Figure 2 shows the TGA results of jute fibre reinforced epoxy composite. There are three significant regions of weight loss due to rise in temperature. The initial low temperature weight loss of composites is due to the removal of moisture from composite, major weight loss due to degradation and volatization of epoxy along with jute fibres present in composites and the residue that are formed after degradation requires higher temperature for subsequent degradation. The initial, major and final weight loss and their corresponding temperature are given in Table 4. The major weight loss of the composite J30 occurs at 510 ºC. Here degradation is shifted to higher temperature which shows increased thermal stability due to stronger adhesion between fibres and matrix as compared to all other composites.
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Linking naturally and unnaturally spun silks through the forced reeling of Bombyx mori

Linking naturally and unnaturally spun silks through the forced reeling of Bombyx mori

Native silks and RSFs are often composed of the same peptide motifs [11], and hence patterns of structural and property differ- ences between the two resulting fibres might be due to both spin- ning and processing condition differences. Not a focus here, several studies have shown how RSF can be post-spun processed (termed ‘‘post-processed’’) in a variety of ways, using chemical or isother- mal treatment or applying postdraw, which influences the struc- tures present [11,12,33–38]. Other studies make the important link between the treatment, the mechanical properties and the protein structure [9,16,39–41]. To date, artificially spun silks (unless considerably post-processed) are unable to match their natural counterparts [42]. This is most likely because the initial spinning and the common post-processing conditions used lead to dissimilar supra-molecular structures [42].
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Behaviour of selected table fats at the dynamic loading

Behaviour of selected table fats at the dynamic loading

The new method of the evaluation of the mechanical behaviour of fats has been designed. This method is based on the evaluation of the fat response to dynamic loading. Dynamic loading has been rea li zed by fall of bar impact. Response function has been represented by the time history of the fat surface displacement. Response of the tested table fats have been evaluated both in the time and fre- quency domain. Two factors aff ected rheology of the examined fat products: temperature of the mea- surement and product origin. The infl uence of fat content can be described namely in the frequency domain. The results obtained between 14 and 20 °C showed signifi cant diff erences in the fat rigidity. table fat, rheology, dynamic loading, surface displacement, spectral function
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Effect of postcure conditions on the dynamic mechanical behavior of water-based polymer-isocyanate adhesive for wood

Effect of postcure conditions on the dynamic mechanical behavior of water-based polymer-isocyanate adhesive for wood

Abstract To study the effect of postcure conditions on the viscoelastic behavior of water-based polymer isocyanate adhesives for wood (API adhesive), dynamic mechanical analysis (DMA) was performed for a simplifi ed model of API adhesives under various postcure conditions. These conditions were achieved by storing the samples at room temperature or by heating them in an oven. Fourier trans- form infrared (FT-IR) spectroscopy was performed to test for residual isocyanate groups (NCO) and isocyanate deriv- atives to elucidate the reaction mechanism under the post- cure conditions. DMA revealed that the postcure conditions led to wide variations in the viscoelastic behaviors of API fi lms. FT-IR analysis confi rmed the decrease of residual isocyanate during postcure treatments. However, the complete consumption of isocyanate could not be achieved under the postcure conditions. A good correlation was found between the DMA result and the chemical changes in the API samples heated above 140°C. However, no cor- relation was observed in the case of the samples heated at temperatures less than 140°C. This implies that postcure conditions led to a difference in the reaction chemistry of API.
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Dynamic mechanical load testing

Dynamic mechanical load testing

Wind load testing of PV modules K.-A. Weiss, M. Assmus, S. Jack, M. Koehl, “Measurement and simulation of dynamic mechanical loads on PV-modules,” Proc. SPIE 7412, Reliability of Photovoltaic Cells, Modules, Components, and Systems II, 741203, 2009.

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Dynamic Mechanical Behaviour of Vigin PP/PET Blends

Dynamic Mechanical Behaviour of Vigin PP/PET Blends

In this paper, virgin Polyethylene tere phthalate has been blended in an elastic extruder with three different types of polypropylenes such as low viscosity Polypropylene (A 5012), high viscosity PP (K 7050) and modified PP (XKP 707W). Dynamic mechanical behaviour such as storage modulus (Er) and dissipation factor (tan δ) of these blends has been determined at different temperatures. Effects of blending ratio on storage modulus and dissipation factor have been determined, compared and analyzed. It has been found that addition of PET increased the storage modulus of PP due to the higher modulus of PET. An additional peak has been observed In tan δ plots obtained for PP/PET blends. This additional peak corresponds to a-relaxation of PET. Type of PP addition has also modified the dissipation factor (tan δ) and storage modulus Er behaviour of blends.
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Decentralized and hierarchical control of robot manipulators

Decentralized and hierarchical control of robot manipulators

2.5 Dynamic 110del Of A Three dof Revolute Robot Manipulator 78 2.5.1 Dynamic Equation Of The Mechanical Linkage 78 2.5.2 Derivative Of The Mechanical Link Torque 85 2.5.3 Model Of The D[r]

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Investigation of Structure-Mechanics-Property Relations in Heart Valve Tissues.

Investigation of Structure-Mechanics-Property Relations in Heart Valve Tissues.

hyperelastic behavior of the soft biological tissue. In the future, the Fung’s constitutive model of the heart valve tissue will be generated and applied to perform computational simulations of tissue response to the mechanical environment via FEA. The curve fitting of the translated stress-strain data will be performed, and constants in the Fung’s constitutive equation will also be determined. Meanwhile, the image of the histological photomicrograph will be imported to the developed image-based finite element system, the Object-Oriented Finite Element (OOF), to build a finite element model, and the microstructure of the tissue will be completely presented by pixel selections of collagen fibers, valvular interstitial cell (VIC) nuclei, and pores. The software ABAQUS (Providence, RI) can be used to define biological tissue constitutive laws for hyperelastic models and will be utilized to perform the finite element analysis by importing the model from OOF into ABAQUS. Via the incorporation of the finite strain theory, stress distribution at both tissue and cellular levels during diastole will be investigated. Upon completion of the finite-deformation constitutive model, quantitative data detailing highly anisotropic and nonlinear mechanical behavior of the heart valve tissues will be provided at both tissue and cellular levels. Furthermore, it will provide a better understanding of the biomechanical regulation mediated by the cell-matrix interaction, such as cellular mechanotransduction, or tissue remodeling in heart valve tissues.
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Dynamic characteristics and processing of fillers in polyurethane elastomers for vibration damping applications

Dynamic characteristics and processing of fillers in polyurethane elastomers for vibration damping applications

The paper explores the rheological characteristics of the polyol filled resins as a means of characterising the nature of the dispersion achieved and the strength of the interactions between polyol and filler. Dielectric relaxation and dynamic mechanical thermal analysis are used to demonstrate the way in which formulation changes influence the breadth and location of the energy loss processes. Finally a study of the damping characteristics of one of the materials will be presented to show how these materials may be used in vibration damping applications.

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The Impact of Free Radical Stabilization Techniques on In Vivo Property Changes in Highly Cross-Linked Polyethylene Acetabular Liners

The Impact of Free Radical Stabilization Techniques on In Vivo Property Changes in Highly Cross-Linked Polyethylene Acetabular Liners

Vickers microhardness indenters and Berkovich nanohardness indenter utilize optical measurement of the residual indentation area (42). While both microindentation and nanoindentation DSI has been performed with orthopaedic UHMWPE retrieval studies (40,43-45), microindentation was selected for use in this study for the following reasons. Per the International Organization for Standardization (ISO) 14577, microindentation is defined as a force applied of less than 2N and indentation depth greater than 0.2 µm and nanoindentation is defined by an indentation depth less than or equal to 0.2 µm (46). Given the difference in depth of indentation, microindentation testing provides a more volume-average response of the material in testing whereas nanoindentation provides a focal assessment of hardness along the material surface. In particular, microindentation averages over the scale of crystalline and amorphous regions while penetrating below the surface polymer. Nanoindentation testing of UHMWPE can demonstrate increased variability due to surface roughness and polymer orientation due to wear or sample preparation, as well as heterogeneity in crystalline and amorphous region distribution in the sample (43,47). Microindentation testing has been established as a reliable method for testing UHMWPE and compares favorably to nanoindentation for the purposes of this study (41). Of the available microindentation testing methods, Vickers microhardness test will be utilized for mechanical testing of HXLPE in this project due to its relative insensitivity to surface conditions, ease and reproducibility of measurement due to the constant indentation geometry. For this testing apparatus, a diamond indenter, in the form of a square-based pyramid with an angle of 136 degrees between the opposite faces (figure 4-1) is pressed onto the sample surface using a predefined force (F) between 25 and 1000 gram-force (gf) over a defined time period (dwell time) of 10 to 15 seconds long per ASTM E384 standards (48). The load is removed and the deformation created in the sample surface is measured using an optical microscope. The Vickers hardness number (HV) is calculated as:
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Dynamic Mechanical Analysis of Compatibilizer Effect on the Mechanical Properties of Wood Flour-High-Density Polyethylene Composites

Dynamic Mechanical Analysis of Compatibilizer Effect on the Mechanical Properties of Wood Flour-High-Density Polyethylene Composites

relative non-abrasiveness, ease of fiber surface modification, wide availability and renew ability. The main disadvantages of natural fibers in composites are the lower processing temperatures allowable, incompatibility between the hydrophilic natural fibers and hydrophobic polymers, and potential moisture absorption of the fibers and in turn, the manufactured composite [2,3]. To enhance the compatibility of the two phases in such composites, a compatibilizer or coupling agent is normally added to the mixture or fiber surface is modified prior to compounding. Gauthier et al. (1998) [4] state that a compatibilizer must be highly reactive to cellulose hydroxyl groups while at the same time having a non-polar chain preferably of the same type as the matrix [4]. While for polypropylene based composites, use of maleic anhydride modified polypropylene (MAPP) has been reported for this purpose, a similar material (MAPE) has proved equally well for polyethylene composites. Conventional static tests are normally used to evaluate the performance of the compatibilizers [5-9]. However, Tajvidi et al. (2003) [10] have successfully used dynamic mechanical analysis to study the compatibilizer effect on the mechanical performance of wood flour PP composites [10].
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Nonlinear dynamic analysis of a four-bar mechanism having revolute joint with clearance

Nonlinear dynamic analysis of a four-bar mechanism having revolute joint with clearance

In general, joints are assumed without clearance in the dynamic analysis of multi-body mechanical systems. When joint clearance is considered, the mechanism obtains two uncontrollable degrees of freedom and hence the dynamic response considerably changes. The joints’ clearances are the main sources of vibrations and noise due to the impact of the coupling parts in the joints. Therefore, the system responses lead to chaotic and unpredictable behaviors instead of being periodic and regular. In this paper, nonlinear dynamic behavior of a four-bar linkage with clearance at the joint between the coupler and the rocker is studied. The system response is performed by using a nonlinear continuous contact force model proposed by Lankarani and Nikravesh [1] and the friction effect is considered by a modified Coulomb friction law [2]. By using the Poincaré portrait, it is proven that either strange attractors or chaos exist in the system response. Numerical simulations display both periodic and chaotic motions in the system behavior. Therefore, bifurcation analysis is carried out with a change in the size of the clearance corresponding to different values of crank rotational velocities. Fast Fourier Transformation is applied to analyze the frequency spectrum of the system response.
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Influence of Nanogels on Mechanical, Dynamic Mechanical, and Thermal Properties of Elastomers

Influence of Nanogels on Mechanical, Dynamic Mechanical, and Thermal Properties of Elastomers

The morphology of the gel particles, as well as the gel filled matrices was analyzed with the help of atomic force microscopy (AFM). AFM studies were carried out in air at ambient conditions (25 °C, 60% RH) using multimode AFM, from Veeco Digital Instruments, Santa Barbara, CA, USA. Topographic height and phase images were recorded in the tapping mode AFM with the set point ratio of 0.9, using silicon tip having spring constant of 40 N/m. The cantilever was oscillated at it resonance frequency of *280 kHz. Scanning was done at least 3 different posi- tions of each sample and the representative images were taken. The latex gel samples were diluted several times before testing with doubly distilled water. A drop of this diluted sample was placed on a freshly cleaved mica sur- face which was allowed to dry before taking the image. In the case of gel filled matrices, very thin cast film samples were used for morphology. Due to the difference in their elastic modulus, one of the phases appears darker (NR) and the other one brighter (SBR) in all the AFM micrographs. The gel filled rubber samples for transmission electron microscopy (TEM) analysis were prepared by ultra-cryo- microtomy using Leica Ultracut UCT, at around 30 °C below the glass transition temperature of the compounds. Freshly cut glass knives with cutting edge of 45° were used to get the cryosections of 50-nm thickness. The microscopy was performed using JEM-2100 (JEOL Ltd., Tokyo, Japan) operating at an accelerating voltage of 200 kV.
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In vitro degradation of PHBV scaffolds and nHA/PHBV composite scaffolds containing hydroxyapatite nanoparticles for bone tissue engineering

In vitro degradation of PHBV scaffolds and nHA/PHBV composite scaffolds containing hydroxyapatite nanoparticles for bone tissue engineering

This polymer is degradable and piezoelectric (and thus might promote bone growth in vivo) and possesses extremely good biocompatibility [6, 8]. Together with highly biocompatibil- ity, the copolymer PHBV has degradation times much longer than the other biocompatible polymers which will allow the scaffolds to maintain its mechanical integrity, until there is sufficient bone growth throughout the implant. PHBV copolymers have been found as minimal inflammatory in long-term studies of subcutaneous implants in mice and rats [9]. By considering these properties, PHBV copolymers may be a suitable candidate to support long-term bone regeneration [10]. The degradation products of PHB and PHBV polymers are the normal constituent of human blood, and hence they exert less inflammatory response to human body than other polymers [6, 11].
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Self-powered pressure sensor based on the triboelectric effect and its analysis using dynamic mechanical analysis

Self-powered pressure sensor based on the triboelectric effect and its analysis using dynamic mechanical analysis

Abstract: Since 2012 there has been a rapid rise in the development of triboelectric nanogenerators due to their potential applications in the field of energy harvesting and self-powered sensors for vibrations, accelerations, touches, pressures and other mechanical motions. This study suggests a novel triboelectric nanogenerator based on the interaction between polyvinylidene fluoride and polyvinylpyrrolidone submicron fibers. Polyvinylpyrrolidone is introduced as a new material for the TENG because of its tendency of losing electrons easily, while polyvinylidene fluoride is selected for its strong- electron attracting ability. Electrospinning is suggested as a fabrication method for the nanofibers due to its simplicity, versatility and low-cost. Furthermore, the paper explores the possibility to use this triboelectric nanogenerator as a self-powered pressure sensor. For this purpose, the nanogenerator is subjected to dynamic mechanic analysis which produces controlled pressure forces applied with a certain frequency. This is the first work to suggest the use of dynamic mechanical analyzer to study the relation between the applied mechanical stimulus and the electric responses of the triboelectric nanogenerator. Eventually the sensitivity of the nanogenerator to different pressures is analysed. A directly proportional relationship is found between the pressure applied and the resultant voltage and current amplitudes. The developed nanogenerator reacts to pressure in real time and as a sensor it exhibits a very high sensitivity and low experimental error for repeated measurements. The main contributions of this study are the development of a novel nanogenerator based on the triboelectric effect between polyvinylidene fluoride and polyvinylpyrrolidone electrospun fibers and the investigation for its potential use as a self- power pressure sensor. Eventually, the paper explores the advantages of dynamic mechanical analyzer for pressure analysis.
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Tai Chi and vestibular rehabilitation improve vestibulopathic gait via different neuromuscular mechanisms: Preliminary report

Tai Chi and vestibular rehabilitation improve vestibulopathic gait via different neuromuscular mechanisms: Preliminary report

One possible reason concentric ankle MEE contribution may have increased significantly in the TC group, but not the VR group, is because the TC and the warm-up exercises improved ankle flexibility. Tight ankles (limited range of motion, ROM) may preclude the optimal structural alignment to coordinate mechanical energy sufficiently to increase propulsion [41], perhaps at the expense of trunk stabilization. Ankle function is important for balance cor- rections in both healthy elderly and vestibulopathic sub- jects [42-44]. A study by Van Deusen et al. [45] found that Tai Chi-like exercises for elders with arthritis resulted in a significant increase in ankle plantar flexion; this finding supports the above contention that the TC group in our study may have increased ankle MEE contribution as a result of increased ankle ROM, ankle moment, or both. The tight coupling between ankle and hip power in gait [19] would also explain the neuromuscular adaptive decrease in hip MEE contribution. Given the importance of ankle-plantar flexors in both propulsion and trunk sta- bility, we conclude that TC teaches optimization of MEE in an effort to control the trunk while improving lower extremity function. The relationship between lower extremity MEE and trunk kinematics for the two treatment groups lends further credibility to this conclusion. As shown in Figure 4, the relationship between change in leg MEE and change in the range of forward trunk velocity was positive for the TC group, and negative for the VR group. Similar relationships were also observed between change in leg MEE and change in peak forward trunk velocity. The observed direct relationship for the TC group suggests that the redistribution of power among ankle, knee and hip joints, which resulted in a net increase in the total MEE of the leg, enabled these patients to attain a faster gait. This observation is expected based on the prin- ciples of TC, which emphasize a vertical alignment inte- grating the head, torso, hips and legs. This concept of integrated alignment is reflected in phrases from the TC classics such as ". suspend the spine like a necklace of pearls" and "movements are initiated in the feet, steered by the waist and administered through the hands." [46]. In contrast, for the VR group, however, the increase in leg MEE was associated with a decrease in both peak and range of trunk velocity. This finding suggests that VR sub- jects, when increasing power generation/absorption with their lower extremities, reduce trunk oscillations during gait, possibly as a way to stabilize the trunk and head. This corrective procedure may not be necessary for TC subjects as they learned to move the trunk more proportionately to total lower extremity MEE, without need to explicitly
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Design Calculation and Performance Analysis of Single Suction Centrifugal Pump

Design Calculation and Performance Analysis of Single Suction Centrifugal Pump

Abstract- Centrifugal pumps are used widely for hydraulic transportation of liquids through pipelines where the requirement of head and discharge are moderate. This paper presents the design of impeller and casing of single suction centrifugal pump and performance analysis of losses. The impeller and the casing are a rotating component and a stationary component. Water enters axial flow through the impeller eyes and exits radial flow in centrifugal pump. The pump casing is to control the liquid to the impeller, transfers into pressure the high velocity kinetic energy of the flow from the impeller discharge and leaves liquid away of the energy having imparted to the liquid comes from the volute casing. The design calculation and performance analysis of single suction centrifugal pump are describe because it is the most essential useful mechanical dynamic machine in fluid works which used for water supply plants, irrigation, industry, steam power plants, hydraulic power service, mine and river water pumping system,
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MECHANICAL AND DYNAMIC MECHANICAL CHARACTERIZATION OF GROUNDNUT SHELL POWDER FILLED RECYCLED HIGH DENSITY POLYETHYLENE COMPOSITES

MECHANICAL AND DYNAMIC MECHANICAL CHARACTERIZATION OF GROUNDNUT SHELL POWDER FILLED RECYCLED HIGH DENSITY POLYETHYLENE COMPOSITES

The current trend of research in the field of natural fibre based composites is the application of dynamic mechanical analysis (DMA) technique. DMA depicts the stiffness stability of the composites with increasing temperature, its glass transition temperature and its viscoelastic nature when stimulated by dynamic loading. Time temperature superposition (TTS) principle is also an important parameter that could be determined by the use of DMA technique. TTS principle is usually used to predict the long term performance of material by the use of the Williams-Landel- Ferry (WLF) equation.
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