The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform

Randall M. German - One of the best experts on this subject based on the ideXlab platform.

  • Densification and Strength evolution in solid-state sintering Part I Experimental investigation
    Journal of Materials Science, 2002
    Co-Authors: Randall M. German
    Abstract:

    Prealloyed bronze (Cu-10Sn) powder and a mixed elemental steel (Fe-2Ni-0.9C) powder were evaluated for Strength evolution during sintering. For the bronze powder, test samples were fabricated using a loose powder casting method, while the steel powder was formed by injection molding. In Situ Strength during sintering was measured using a bending fracture test. Primary focus was on measuring the effects of sintering temperature and time on in Situ Strength evolution. Sintering temperature had the most significant effect, but the Strength underwent significant gains prior to densification. The results are explained by the competition among interparticler neck growth, densification, and thermal softening. Sinter Strengthening is initially governed by interparticle bonding, followed by a contribution from densification at high temperatures. However, high temperatures also lead to significant Strength degradation due to thermal softening. Densification is favored by the declining in Situ Strength associated with thermal softening at high temperatures.

  • Densification and Strength evolution in solid-state sintering Part II Strength model
    Journal of Materials Science, 2002
    Co-Authors: Randall M. German
    Abstract:

    A compact gains Strength in sintering through low-temperature interparticle bonding, followed by further Strength contributions from high-temperature densification. On the other hand, thermal softening substantially reduces a compact's Strength at high temperatures. Therefore, the in Situ Strength during sintering is determined by the competition among interparticle neck growth, densification, and thermal softening. Distortion in sintering occurs when the compact is weak. Most Strength models for sintered materials are semi-empirical relations based on the sintered fractional density. These models do not include microstructure or sintering cycle parameters; thus, they do not provide guidelines for thermal cycle design to improve compact dimensional control. A Strength evolution model is derived which combines sintering theories and microstructure parameters, including interparticle neck size, solid volume fraction, and particle coordination number. The model predicts sintered Strength and when combined with thermal softening gives a good prediction of in Situ Strength. The validity of the model is verified by comparison to experimental data for sintered and in Situ Strength of bronze and steel powders.

  • In Situ Strength of evolution of P/M compacts during sintering
    International Journal of Powder Metallurgy, 2000
    Co-Authors: Gregory A. Shoales, Randall M. German
    Abstract:

    The fabrication of dimensionally precise powder metal components results frequently in a trial and error approach to determine the various process parameters. Not the least of these parameters are the time and temperature profiles of the sintering cycle. These sintering variables, combined with furnace thermal gradients and component geometry are usually the key factors leading to distortion. Resistance to distortion resides in the Strength of the component and it is vital therefore to know how the Strength of a green compact evoives during the sintering portion of the manufacturing process. A device and a method were developed to characterize the in Situ evolution of Strength in response to the thermal parameters of sintering. The specific Strength investigated and modeled was transverse rupture. We have used the device to characterize successfully Strength evolution in various ferrous and non-ferrous alloys as well as ceramics. This work presents the results for bronze compacts and represents the first successes in modeling in Situ Strength evolution with respect to sintering time and temperature. The consequence of the model is to identify sintering time and temperature combinations that minimize distortion and improve dimensional tolerances.

  • In Situ Strength evolution during the sintering of bronze powders
    Metallurgical and Materials Transactions A, 1998
    Co-Authors: Gregory A. Shoales, Randall M. German
    Abstract:

    Powder metallurgy (PM) allows the fabrication of complex net-shaped components. Accurate design specification of these components requires precise prediction of the compact’s response to sintering process parameters. Nonuniform sintering responses such as strain gradients can result in process failures such as permanent deformation and cracks. To avoid these types of process failures without costly trial-and-error design, the most important response to predict is the compact’s Strength as it evolves during the sintering process. A device and method have been developed to characterize the in Situ Strength evolution as a function of various sintering process parameters. The specific Strength parameter investigated and modeled in this article was transverse rupture. This Strength was precisely determined for 90Cu-10Sn bronze in response to various combinations of temperature, heating rate, and heating time. The consequence of this work is to identify thermal cycles that minimize distortion and otherwise improve dimensional tolerances.

B. L. Karihaloo - One of the best experts on this subject based on the ideXlab platform.

  • Optimum in Situ Strength design of laminates under combined mechanical and thermal loads
    Composite Structures, 1999
    Co-Authors: Jianxiang Wang, B. L. Karihaloo
    Abstract:

    In this paper, optimum laminate configurations are sought for multidirectional fibre-reinforced composite laminates under combined in-plane mechanical and thermal loads. The design objective is to enhance the value of the loads over and above the first-ply-failure loads which are judged by a transverse failure criterion and the Tsai-Hill criterion, respectively. The in Situ Strength parameters previously obtained are incorporated in these criteria. It is found that the optimum designs under combined mechanical and thermal loads are not the same as those under pure mechanical loads for three of the four loading cases studied. For all cases the optimum loads are significantly larger than those for a quasi-isotropic design.

  • Optimum in Situ Strength design of laminates under combined mechanical and thermal loads
    1999
    Co-Authors: Wang J, B. L. Karihaloo
    Abstract:

    In this paper, optimum laminate configurations are sought for multidirectional fibre-reinforced composite laminates under combined in-plane mechanical and thermal loads. The design objective is to enhance the value of the loads over and above the first-ply-failure loads which are judged by a transverse failure criterion and the Tsai-Hill criterion, respectively. The in Situ Strength parameters previously obtained are incorporated in these criteria. It is found that the optimum designs under combined mechanical and thermal loads are not the same as those under pure mechanical loads for three of the four loading cases studied. For ail cases the optimum loads are significantly larger than those for a quasi-isotropic design. (C) 2000 Elsevier Science Ltd. All rights reserved.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000089300500026&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Materials Science, CompositesSCI(E)EICPCI-S(ISTP)1

  • Optimum In Situ Strength Design of Composite Laminates. Part I: In Situ Strength Parameters
    Journal of Composite Materials, 1996
    Co-Authors: J. Wang, B. L. Karihaloo
    Abstract:

    In Part I of this two-part paper, a cracked fibre-reinforced angle-ply composite laminate is analysed using fracture mechanics. Based upon this analysis, a set of in Situ Strength parameters for unidirectional laminae in a multidirectional laminate is proposed. The in Situ Strength parameters take into account the influence of adjacent laminae and thickness of a particular lamina upon its transverse tensile and in-plane shear Strengths when it is used in a multidirectional laminate. These Strength parameters are then employed to calculate a stress norm which determines how close the stress state in the lamina is to its failure state. In the companion paper (Part II), the stress norm is incorporated into the formalism of an optimization problem in order to enhance the load bearing capacity of multidirectional laminates.

  • Optimum In Situ Strength Design of Composite Laminates. Part II: Optimum Design
    Journal of Composite Materials, 1996
    Co-Authors: J. Wang, B. L. Karihaloo
    Abstract:

    The stress norm developed in Part I is incorporated into the formalism of an optimization problem in order to enhance the load bearing capacity of multidirectional laminates. The optimization problem is solved for symmetric laminates subjected to any combination of in-plane loads. In this problem, the stress norm is the design objective to be minimized whereas the ply angles and thicknesses are the design variables. The solution of the formulated min{max) optimization problem is obtained by the bound-formulation method and mathematical programming. The gradients of objective functions and constraints needed in this method are calculated by a mixed analytical/numerical procedure. The results show that the optimization technique based on the in Situ laminae Strength parameters is a promising tool in the design of the composite laminates. The load bearing capacity of an optimally designed laminate can be increased several fold compared with that of a conventionally designed laminate.

  • Fracture mechanics and optimization — a useful tool for fibre-reinforced composite design
    Composite Structures, 1995
    Co-Authors: Jianxiang Wang, B. L. Karihaloo
    Abstract:

    This paper will demonstrate the application of fracture mechanics and optimization techniques for the optimum design of fibre-reinforced composite laminates (FRC). First, a boundary-value problem of a cracked composite laminate is solved within the framework of linear elastic fracture mechanics (LEFM). The solution relates the stress intensity factor at a crack tip and the crack-induced interfacial stresses to the laminate configuration. These results are then used in two types of the optimum design of fibre-reinforced composite laminates. In the first type of optimum design, namely a crack-insensitive design of the laminate, the crack driving force and interfacial principal tensile stress are both minimized by using single- and multicriterion optimization techniques. The second type of optimum design involves in Situ Strength design of multidirectional angle-ply laminates. In this case, a set of in Situ Strength parameters are proposed based on theoretical analysis and experimental observations. This optimization problem is a min {max} one and non-differentiable. A proper treatment of the non-differentiability is introduced and the min {max} optimization problem is converted into a differentiable single-criterion one using the bound-formulation technique. All the optimization problems are solved by non-linear mathematical programming. The results show that optimization can greatly enhance the load carrying capacity of the laminates.

Mahmood Naderi - One of the best experts on this subject based on the ideXlab platform.

  • THE USE OF FRICTION-TRANSFER METHODS IN PREDICTION OF IN-Situ Strength OF CONCRETE
    2008
    Co-Authors: Mahmood Naderi, Khomeini
    Abstract:

    ةـصلاخلا : فوس مد قن اذ ه ي ف ثحبلا جل ةر كتبم ة قيرط ريمد تلا ة يئز ت فر ع ـ ب ” كا كتحلاا ل قن “ ، را بتخلال ك لذو ةنا سرخلا ةوقل يعضوملا . د قو هرطق بقث لمعب ا نمق 50 ه قمعو م لم 25 ةنا سرخلا حطس يف م لم ، ا نمق م ث نمو بقثلا قوف ةكسام ةادأ تيبثتب ، حاتفم انمدختساو سايقل مزعلا طاغضنلاا ةوق . و د نع نارود مزع ىصقأ انمدختسا قلازنلاا ) لشفلا ( ةريا عملا لوادج مادختساب ةيبيعكتلا ةوقلاو طاغضنلاا ةوق ريدقتل . ا مآ ا نراق ني ب ثحبلا اذ ه يف ة يبيعكتلا ةو قلاو طاغضنلاا ةو ق ريد قت يف ةمدختسملا اهتلايثمو ةقيرطلا هذه ، و انيب قرطلا هذ ه ني ب تاطابترلاا . د قو يلاو ح ة ساردلا هذ ه جئا تن ي ف ريا غتلا لد عم نا آ % 8.6 ، ة فلتخملا طا بترلاا تلاد عمو 0.98 و 0.96 . و أ تر هظ ة قيرطلا هذ ه ن ع جتا نلا ف لتلا نأ ةدود حملا رصانعلا ل يلحت جئا تن ) كا كتحلاا ة قيرط ( لايئ ض نا آ روصحمو ا بقثلا ةقطنم لخاد . و ةقيرطلا هذه ةعاجنب ةساردلا هذه يصوت جئاتنلا هذه ىلع دامتعلااب .

  • new twist off method for the evaluation of in Situ Strength of concrete
    Journal of Testing and Evaluation, 2007
    Co-Authors: M R Mitchell, R E Link, Mahmood Naderi
    Abstract:

    This paper introduces an innovative partially destructive method called “Twist-off,” for the assessment of in Situ concrete Strength. In this method, a 40 mm diameter metal probe is bonded to a concrete surface by means of a high Strength epoxy resin adhesive. To measure the concrete compressive Strength, a torque is applied using an ordinary torque wrench and the maximum torque or shear stress at failure is used to estimate the cube compressive Strength by means of a calibration graph. The relationship between the results of this new method and the compressive Strengths of concrete cores as well as the correlation of this method with friction-transfer method are also presented in this paper. The average coefficient of variation of the results of this method was seen to be of the order of 8 % and the correlation coefficients of its comparative results with concrete cube and core compressive Strengths were found to be 0.98 and 0.90, respectively. In order to assess the performance of this method on site, tests were undertaken on a number of concrete structures. Based on these results, this method is suggested for in Situ determination of concrete Strength.

  • Assessing the in Situ Strength of concrete, using new twist-off method
    International Journal of Civil Engineering, 2006
    Co-Authors: Mahmood Naderi
    Abstract:

    This paper introduces an innovative partially destructive method, called "Twist-off", for the assessment of in Situ concrete Strength. In this method a 40mm diameter metal probe is bonded to a concrete surface by means of a high Strength epoxy resin adhesive. To measure the concrete compressive Strength, a torque is applied using an ordinary torque-meter and the maximum shear stress at failure is used to estimate the cube compressive Strength by means of a calibration graph. The relationship between the results of this new method and compressive Strengths of concrete cores is also presented in this paper. The average coefficient of variation of the results of this method was seen to be of the order of 8 percent and the correlation coefficients of its comparative results with concrete cube and core compressive Strengths were found to be 0.97 and 0.90 respectively. In order to assess the performance of this method on site, tests were undertaken on a number of buildings. Although the method was found to perform well but with some of the structures tested, the differences between the Strengths of sample cubes and estimated in Situ compressive Strength of concrete were seen to be significant.

  • Friction-transfer test for the assessment of in Situ Strength and adhesion of cementitious materials
    Construction and Building Materials, 2005
    Co-Authors: Mahmood Naderi
    Abstract:

    Abstract Since in concrete industry, the quality control is generally accomplished by the testing of separately prepared samples, the accurate estimate of the in Situ Strength of concrete has become a necessity. The main discrepancies between the measured cube Strength and the actual in Situ Strength of concrete, relates to their different conditions associated with the development of Strength. In addition, due to chemical deterioration or damage, accurate estimate of in Situ concrete Strength provides valuable information about the present Situation of the structure, when making decisions about the required repair and/or Strengthening systems. The Friction-Transfer method, which is described in this paper, can be used to estimate the in Situ Strength of concrete and other materials. In this method a specially devised apparatus fits on to the top of the partial core and is clamped to it. To measure the concrete compressive Strength, a torque is applied using an ordinary torque-meter and the maximum shear stress at failure is used to estimate the cube compressive Strength by means of a calibration graph. In order to measure the adhesion between different layers of cementitious and/or resinous materials, their torsional shear Strengths are calculated along the failed inter-facial surfaces of the layers. Laboratory and in Situ tests, to evaluate the performance of the method are described. Also in view of the accurate and reliable results attainable, some specific applications are proposed.

Ruy Paulo Philipp - One of the best experts on this subject based on the ideXlab platform.

  • in Situ Strength of coal bed based on the size effect study on the uniaxial compressive Strength
    International journal of mining science and technology, 2014
    Co-Authors: Clovis Gonzatti, L Zorzi, I M Agostini, J A Fiorentini, Antonio Pedro Viero, Ruy Paulo Philipp
    Abstract:

    Abstract In the early 1990s, the Foundation for Science and Technology of Rio Grande do Sul State (CIENTEC) developed a pioneering study in Brazil, related to the simultaneous mining of multiple coal seams. One of the activities included detailed studies on the geomechanical characterization of materials present in the Irapua coal seam, under exploitation in the A-Sangao Mine, located near the city of Criciuma-SC, within the South-Catarinense coalfield. The goal of the laboratory tests was to define the behavior of the uniaxial compressive Strength of the Irapua coal seam and establish a first approximation for the in Situ Strength value of this coal seam, since existing knowledge is solely based on practical mining experience over the years. Large samples of the coal seam were collected, using special techniques to maintain the integrity of the material, and a set of 56 uniaxial compression tests in cubic specimens, with side length ranging from 4.5 to 31 cm, were conducted in laboratory. This paper describes the experimental techniques used in the assays, and also presents the uniaxial compression Strength results obtained. Moreover, important aspects of this type of study are considered, highlighting the size effect for the carbonaceous bed and the estimation of in Situ Strength values for the Irapua coal seam.

Yuanming Xia - One of the best experts on this subject based on the ideXlab platform.

  • An experimental study on the in Situ Strength of SiC fibre in unidirectional SiC/Al composites
    Composites Part A: Applied Science and Manufacturing, 2003
    Co-Authors: Wen Huang, Xu Nie, Yuanming Xia
    Abstract:

    Abstract In order to investigate the effect of strain rate and high temperature exposure on the mechanical properties of the fibre in the unidirectional fibre reinforced metal-matrix composite, in Situ SiC fibre bundles are extracted from two kinds of SiC/Al composite wires, which are heat-treated at two different temperatures (exposed in the air at 400 and 600 °C for 40 min after composition). Tensile tests for these two fibre bundles are performed at different strain rates (quasi-static test: 0.001 s −1 , dynamic test: 200, 700, and 1200 s −1 ) and the stress–strain curves are obtained. The experimental results show that their mechanical properties are rate-dependent, the modulus E , Strength σ b and unstable strain e b (the strain corresponding to σ b ) all increase with increasing strain rate. Compared with the mechanical properties of the original SiC fibre, those of the two in Situ fibres degrade to some extent, the degradation of the in Situ fibre extracted from the composite wire exposed at 600 °C (hereafter referred to as in Situ fibre 2) is more serious than that of the in Situ fibre extracted from the composite wire exposed at 400 °C (hereafter referred to as in Situ fibre 1). The mechanism of the degradation is investigated. A bi-modal Weibull statistical constitutive equation is established to describe the stress–strain relationship of the two in Situ fibre bundles. The simulated stress–strain curves agree well with the experimental results.

  • In Situ Strength distribution of carbon fibers in unidirectional metal-matrix composites-wires
    Composites Science and Technology, 2001
    Co-Authors: Yuanxin Zhou, Yuanming Xia
    Abstract:

    Abstract Based on an etching method and the fiber-bundle tensile testing technique, a new method has been developed for the testing and characterization of the Strength distributions of in Situ fibers in unidirectional aluminum-matrix-composite wires. According to this method, a systematic study on in Situ properties of T300 fiber and M40J fibers in MMCs wires have been performed at strain rates ranging from 0.001 to 1300 1/s. Experimental results show that both T300 fiber and M40J fibers are strain-rate insensitive materials. Results also show that the modulus, ultimate Strength and unstable strain of two fibers have been degraded to some degree by high-temperature processing. Micrographs indicate that there are obvious crack distributions on the surfaces of in Situ fibers and this is the main reason for the decreasing fiber Strength. On the basis of the fiber-bundles model and the statistical theory of fiber Strengths, the distribution parameters for in Situ fiber Strength have been obtained. The evaluated stress/strain curves from the theoretical model are in good agreement with the test data. Statistical analysis results show that the high-temperature manufacturing processing only affects the Weibull scale parameter, σ 0 , of T300 fibers and does not affect the shape parameter, β whereas for M40J fibers, both the shape and scale parameters have been changed by high-temperature manufacturing processing.