Papers by Keyword: DMA

Abstract: Mechanical fatigue due to repeated thermal shock cycling is of great importance for most materials intended for refractory applications. This work explores thermal shock resistance and cyclic thermal shock effects of cordierite ceramic made from clay-containing mixtures. Different means of detection of change in modulus of elasticity have been employed including impulse excitation and dynamic-mechanic tests (DMA). Results have shown that the elastic modulus of cordierite ceramic gradually decreases over thermal shock cycles, the sharpest change being observed after the first cycle. Unlike synthetic cordierite ceramic material, clay-substituted cordierite composites show "self-healing" effect, which can be explained by the gradual filling of cracks with glassy phase that leads to the strengthening of the whole structure of material. This effect is directly dependent upon the composition of the sample and the material with lesser amount of glassy phase can be characterized with the largest inertia of this effect.

Abstract: Nowadays the use of glass fibers in development of polymer composites creates a very interesting research area aiming to achieve multiple outputs to different applications. The use of thermoplastic composites reinforced with glass fibers in engineering applications like automotive industry has increased considerably in the last few decades. These composites combine high mechanical strength properties, reduced mass, easy processing and corrosion resistance. The shifting from metals to engineering composites pushes towards lightweighting benefits which results in improved fuel efficiency. This paper is focused on the assessment of polymer composites properties on the basis of polyamides (PA6.6) with the short (GF) and long glass fibres (LGF). The bulk characterization of all samples has been made by Dynamic Mechanical Analysis (DMA) depending on temperature, stress frequency and the weight percentage of reinforcement in matrix.

Abstract: A new kind of structural damping composites was prepared by interleaving polyamide nonwoven fabrics (PNF) between the carbon fiber reinforced epoxy composite laminates. The damping behaviors of the composites made were experimentally investigated using cantilever beam test and dynamic mechanical analysis. The damping ratios of the nonwoven fabrics interleaved composites were compared with the ones of non-interleaved composites. In addition, the interlaminar shear strength and flexible modulus of the composites were also investigated, as well as the composite compression after impact (CAI), Mode I and Mode II interlaminar fracture toughness (G_IC and G_IIC), in order to evaluate the influence of the polyamide nonwoven fabric layers on the composite mechanical properties. It has been observed that the interleaved polyamide nonwoven fabric layers greatly improved the composite damping loss factors, and the composites containing 7 layers of PNF showed the best damping behavior. Meanwhile, the addition of PNF showed a negligible influence on the composite flexible strength and modulus and interlaminar shear strength. Most importantly, the CAI, G_IC and G_IIC tests indicated that the composite interlaminar toughness and impact resistance were significantly improved by the interleaved PNF. Finally, the reinforcing mechanism of this kind of composites is discussed.

Abstract: The paper analyses results of experimental research of homogeneous and heterogeneous solid rocket propellants. The homogeneous sample PAC with density 1.58 g/cm³ and heterogeneous sample H2 with density 1.77 g/cm³ were both subjected to complex thermo-mechanical analysis. The thermo-physical properties of both samples were determined using KD2 Pro apparatus made by Decagon Devices, Inc. (USA). The temperature characteristics of thermal conductivity k (T), thermal diffusivity D(T), and volumetric heat capacity C(T) were measured within the temperature range from-20⁰ C to +80⁰ C. Mechanical properties such as storage modulus (E’), loss modulus (E’’) and tan (delta) were measured using Netzsch DMA 242C analyser within temperature range from-120⁰ C to +80⁰ C at heating rate of 2K/min. The rectangular test samples were subjected to the dual cantilever mode with frequency f = 1Hz recommended by the NATO 4540 standard. Special attention was devoted to determining the glass transition temperature and softening temperature of the propellants. The temperature values obtained during DMA experiments supported by thermo-physical properties are essential for safe usage of solid rocket propellants under operating conditions and they may be applied in numerical modeling of temperature and thermal stress distributions of such materials.

Abstract: In this paper the results of storage modulus (E’), loss modulus (E’’) and damping parameter tan (δ)=E''/E' of epoxy resins Epidian 57 and L285 with curing agents Z1 and LH285, respectively are presented. In addition to this the stress-strain and thermal expansion characteristics of Epidian 53, 57 and L285 were obtained experimentally in order to compare Dynamic Mechanical Analysis (DMA) results. Temperature range of DMA investigations using Netzsch (Germany) DMA 242C analyzer was from-120 °C to +110 °C at the heating rate of 1 K/min with frequency of {0.1, 1, 10} Hz, respectively. Netzsch DIL 402C dilatometer was used to study the thermal expansion of the tested samples within temperature range from 30 °C to 80 °C at 1 K/min of heating and cooling rates, respectively and Huang TA computer servo control material testing machine HT-2402 was applied to determine the stress-strain characteristics. Measurements of sample elongation ΔL and physical α* were performed twice in heating and cooling cycles. The glass transition temperature T_g determined from maximum of tan (δ) curve at f = 1Hz was equal to 76.7 °C for E57 and 87.2 °C for L285. It has been observed durable deformed shape of L285 sample with deflection in the middle about 5 mm just after finishing the DMA first run of heating which significantly affected DMA results during the second run of heating

Abstract: Process induced residual stresses may play an important role under service loading conditions for fiber reinforced composite. They may initiate premature cracks and alter the internal stress level. Therefore, the developed numerical models have to be validated with the experimental observations. In the present work, the formation of the residual stresses/strains are captured from experimental measurements and numerical models. An epoxy/steel based sample configuration is considered which creates an in-plane biaxial stress state during curing of the resin. A hole drilling process with a diameter of 5 mm is subsequently applied to the specimen and the released strains after drilling are measured using the Digital Image Correlation (DIC) technique. The material characterization of the utilized epoxy material is obtained from the experimental tests such as differential scanning calorimetry (DSC) for the curing behavior, dynamic mechanical analysis (DMA) for the elastic modulus evolution during the process and a thermo-mechanical analysis (TMA) for the coefficient of thermal expansion (CTE) and curing shrinkage. A numerical process model is also developed by taking the constitutive material models, i.e. cure kinetics, elastic modulus, CTE, chemical shrinkage, etc. together with the drilling process using the finite element method. The measured and predicted in-plane residual strain states are compared for the epoxy/metal biaxial stress specimen.

Abstract: Finite-element (FE) analysis is important instrument for prediction of plastic car bumper tests. Accuracy of FE analysis depends on accuracy of material input data. It has developed experimental methodology for identification of mechanical properties. The methodology leads to more accurate material input data for numerical simulations.

Abstract: The development of multi-core processors has provided a good solution to applications that require real-time processing and a large number of calculations. However, simply exploiting parallelism in software is hard to make full use of the hardware performance. This paper studies the parallel programming and optimization techniques on TMS320C6678 multicore digital signal processors. We firstly illustrate an implementation of a selected parallel image convolution algorithm by OpenMP. Then several optimization techniques such as compiler intrinsics, cache, DMA are used to further enhance the application performance and achieve a good execution time according to the test results.

Abstract: Cement asphalt mortar (CA mortar) is one of key structures of slab ballastless high-speed railway. Cement and asphalt emulsion are the main two components of CA mortar, making it possess the viscoelastic properties of viscoelastic materials, which is one of the infancy of the current study. In this paper, DMA method was adopted to investigate the viscoelastic properties of CRTS II CA mortar. Viscoelastic properties of CA mortar at different temperatures were investigated and were compared with the numerical simulation results of Burgers model. The results of the simulation fit in well with the data from the experimental-scale column, so we can study the dynamic modulus of CA mortar using the Burgers model in the temperature range of CA mortar.

Abstract: As the demand of higher image quality and greater processing capabilities are growing, obtaining higher data bandwidth for on-chip processing is becoming a more and more important issue. DMA (Direct Memory Access) component, as the key element in stream processing SoC (System on Chip) [1], should be deeply researched and designed to satisfy the high data bandwidth requirement of processing units. In this paper, we introduce a scalable high-performance DMA architecture for complex SoC to satisfy rigorous high sustained bandwidth and versatile functionality requirements. Several techniques and structures are proposed in this paper. A state-in-art verification environment is built for our design to fully verify its functionality. At the end of the paper, the tape-out results are provided. The whole implementation has been silicon proven to be functional and efficient.