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  • 1.
    Antti, Marta-Lena
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Babushkin, O
    Luleå tekniska universitet.
    Shen, Z
    Nygren, M
    Warren, R
    Thermal expansion behaviour of high melting point oxides1999Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 164-165, s. 279-282Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal expansion characteristics of the reinforcement and matrix constituents in ceramic composites have a strong influence on a number of aspects of the composite performance. Thus the toughness and strength of the composite can be influenced by local residual stresses due to the thermal expansion mismatch of different phases. Moreover, in individual polycrystalline phases, local stress variations from grain to grain, generated as a result of anisotropy of thermal expansion in combination with anisotropy of elasticity can influence strength and toughness in similar ways. In the present study, reported data on the thermal expansion coefficients of oxides having potential as constituents in high temperature composites are reviewed and complemented with additional measurements made using high temperature X-ray diffraction

  • 2.
    Ashkin, A.
    et al.
    Luleå tekniska universitet.
    Ashkin, D.
    Luleå tekniska universitet.
    Babushkin, O.
    Luleå tekniska universitet.
    Investigation of α-sialon formation by high temperature X-ray diffraction1994Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 89-91, s. 373-377Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A technique for following sialon formation in situ by high temperature x-ray diffraction (HT-XRD) was developed. The composition chosen for study was an yttrium α-sialon with x = 0.4. Powder compacts containing silicon nitride, aluminum nitride and yttria powders were pre-sintered at 1350 °C and then studied by HT-XRD at temperatures between 1450 and 1580 °C and nitrogen pressures of 0.11 MPa. The furnace was made from graphite coated with porous silicon nitride/silicon carbide. The coating prevented silicon carbide formation in the sample up to 1600 °C. X-ray diffraction results show the formation of a Y10Al2Si3O18N4 phase at 1350 °C, which dissolved to form α-sialon and other phases at higher temperatures. The amounts of α-sialon formed are similar to the amounts reported by other authors. An empirical method was used for the calculation of activation energy for the silicon nitride to α-sialon transformation and resulted in a value of 330 kJ mol

  • 3.
    Asp, Leif
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nilsson, Karl-Fredrik
    SICOMP AB, Swedish Institute of Composites.
    Delamination criticality in slender compression-loaded composite panels2002Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 221-222, s. 3-16Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a damage tolerance model based on the assumption of delamination criticality in compression loaded slender composite panels is outlined. In particular, the verification of the model by comparison between numerical predictions and experimental results is reviewed. Growth of shallow delaminations in slender panels is shown to be promoted by the global buckling of the panel. Consequently, care must be taken if structures with delaminations are to be allowed to buckle. In the paper, application of the model for aircraft design is briefly discussed. The overall predicted panel behaviour agrees with observations for test coupons. However, very small geometrical changes are shown to have tremendous effects on the predicted behaviour. Consequently, in structural design one must consider the sensitivity of geometrical conditions on the predicted behaviour. Therefore, reduction of the structural item into a design element is suggested. To generate conservative designs the suggested design element is to represent the worst case

  • 4.
    Chen, Yuhong
    et al.
    School of Material Science and Engineering, Beifang University for Nationalities Yinchuan, Ningxia.
    Jiang, Liang
    School of Material Science and Engineering, Beifang University for Nationalities Yinchuan, Ningxia.
    Yang, Qixing
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Fenglan, Han
    School of Material Science and Engineering, Beifang University for Nationalities Yinchuan, Ningxia.
    Identification of Fe-containing phase in oxidation process of BOF slag2017Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 726, s. 564-568Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, the Fe-containing phases in BOF slag were identified before and after oxidized with atmospheric air. XRD and SEM with EDS results showed that The element Fe existed in slag in the form of calcium ferrite, wustite solid solution and hematite. Mg solid solute in wustite. After oxidized, magnetite became the major mineral phase in slag and Mg+ replace the Fe2+ of magnetite crystal to form spinel

  • 5.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Performance of non-crimp fabric composites in shear2010Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 425, s. 45-59Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experimental results of performance of non-crimp fabric composites are presented in this paper. In order to characterize in-plane shear properties of these composites, tensile and compression tests of [±452]S specimens were carried out. Two directions of loading are considered: warp (Shear warP: SP) and weft (Shear wefT: ST). This corresponds to laminates with the following lay-up: SP = [+45/-45/+45/-45]S; ST = [-45/+45/-45/+45]S. Although both types of laminates are cut from the same plate, mechanical performance in tension is rather different: laminate cut in weft direction exhibit higher shear modulus, shear strength and shear strain at failure than samples cut in warp direction. Fractography showed that different behavior of the materials is caused by much earlier damage initiation and accumulation in SP laminates. Analysis of images obtained from optical microscopy indicated that premature failure is most likely caused by stitches that prevent free rotation of bundles (shear deformation).

  • 6.
    Kou, S.Q.
    Luleå tekniska universitet.
    Fracture systems caused by mechanical indentation in medium or hard rocks1998Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 149, nr 2, s. 941-946Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fracture systems in brittle rocks induced by indentation are presented. These are based on numerous experimental results. Two models have been developed to account for the experimental observations and elucidate the failure mechanisms induced during indentation. One model concerns the indentation depth and the other describes the length of radial/median cracks remaining in the rock. Equations deduced from both models correlate well with experimental results in the laboratory. Modification of the equations makes it possible to take the fracture systems in the deep underground into consideration. The equations can serve for general use in many medium or hard rocks with different dimensions of indenters

  • 7.
    Li, Lianchong
    et al.
    Research Center for Numerical Tests on Material Failure, Dalian University.
    Tang, Chunan
    Center for Rock Instability & Seismicity Research, Northeastern University, Shenyang.
    Lindqvist, Per-Arne
    Fracture Behavior in a Rock Pillar Subjected to Coupled Thermo-Mechanical Loading2006Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 324/325, s. 443-446Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using RFPA code, analyses have been carried out to investigate the stability of a rock pillar in a experiment for nuclear waste repositories, the numerically obtained stress field, temperature distribution, failure pattern of the pillar rock and associated AE events are all agree well with the in-situ data. Minor fracture initiation may take place in the vicinity of the boreholes after heating. Heating induces minor spalling at central pillar wall for 0.5 m sections below the tunnel floor, but the area of spalling is found to be limited. The core of the pillar remains intact for stress conditions corresponding to 120 days of heating which not only prove that the proposed technique provides a powerfully alternative and effective approach for the study on thermal-mechanical-damage coupling mechanism but also provide meaningful guides for the experiment design and associated applications.

  • 8.
    Lindgren, Lars-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Fisk, Martin
    Materials Science, Technology and Society, Malmö Högskola.
    Dislocation density based plasticity model coupled with precipitate model2013Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 535 - 536, s. 125-128Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dislocation density based plasticity model is applied to two variants of steels. One is an austenitic (fcc) stainless steel with ordered precipitates and the other is a Ti-Nb microalloyed (bcc) steel. Precipitate distributions are measured and this information is combined with appropriate precipitate hardening models. The flow stress model is also calibrated for an nickel-based superalloy where it is combined with a model for precipitate growth

  • 9.
    Lundmark, P.
    et al.
    Luleå tekniska universitet.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Modeling thermo-mechanical properties of damaged laminates2003Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 251-252, s. 381-387Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we present a theoretical framework which allows us to determine the whole set of thermo-mechanical constants of the damaged laminates a function of crack density in different layers. In this approach closed form expressions are obtained which contains the ply properties, laminate lay-up and crack density as the input information. It is shown that the crack face opening and crack face sliding displacement normalized with respect to load are important parameters in these expressions affecting the level of properties degradation. They are determined in this paper using generalized plain strain FEM analysis results for non-interactive cracks. The methodology is validated and the possible error introduced by the non-interactive crack approach is estimated comparing with the 3-D FEM solution for cross-ply laminate with two systems of orthogonal cracks in plies. A limited number of experimental data are presented and used for further verification. [Material: GF/EP.]

  • 10.
    Nilsson, M.
    et al.
    CSIRO, Lindfield, NSW.
    Warren, Richard
    Luleå tekniska universitet.
    Swain, M.V.
    CSIRO, Lindfield, NSW.
    A Critical Appraisal of the Interfacial Toughness of Ceramic Matrix Composites Using Indentation Techniques1999Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 161-163, nr 675-680, s. 675-680Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Advanced ceramic matrix composites provide a challenge for both manufacturer and user necessitating better techniques to critically appraise their properties. Interfacial toughness and the change of this property with application time at elevated temperature in hostile environments is of paramount importance for structural integrity/reliability of these materials. The present study investigates two such composite systems; a mullite matrix reinforced with silicon carbide fibres, and a novel oxide composite using sapphire fibres within an alumina-zirconia matrix. The interfacial toughness between the fibres and matrix was evaluated using nano- and micro-indentation fracture toughness methodologies. The results are interpreted in terms of recent theoretical interfacial fracture mechanics analysis by Hutchinson and Suo[1] for cracks approaching and extending along an interface. Nano-indentation has also been used to evaluate the intrinsic elastic/plastic properties of the CMC materials

  • 11.
    Tanpichai, Supachok
    et al.
    Learning Institute, King Mongkut's University of Technology, Thonburi, Bangkok.
    Witayakran, Suteera
    Kasetsart Agricultural and Agro-Industrial Product Improvement Institute, Kasetsart University, Bangkok.
    Mechanical properties of all-cellulose composites made from pineapple leaf microfibers2015Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 659, s. 453-457Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pineapple leaf microfibers were firstly prepared using steam explosion, and all-cellulose composites were subsequently prepared using a surface selective dissolution process with the solvent of lithium chloride and N,N-dimethylacetamide (LiCl/DMAc). Mechanical properties and surface morphology of all-cellulose composites with immersion times of pineapple leaf microfibers in the solvent of LiCl/DMAc were investigated using tensile testing and scanning electron microscopy, respectively. The tensile strength of the all-cellulose composites with 120 min-immersion time was approximately 28 times higher than that of the pineapple leaf microfiber mats. These biocomposites made from pineapple leaf microfibers could be one of the potential alternatives to replace glass fiber reinforced composites.

  • 12.
    Varna, Janis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hansson, T.
    Volvo Aero Corporation.
    Failure Mechanisms and the Macro-Response of Carbon Fiber Reinforced SiC Matrix Composites1999Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 164-165, s. 209-212Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Inelastic response of ceramic matrix woven 2.5 -D C/SiC composites have been analyzed using quasi-static test data. The changes in composite stiffness properties (elastic modulus, in-plane and out-of-plane Poisson's ratio) are determined experimentally. The increase of residual strains with the applied stress is analyzed and described by simple functions. Micromechanical damage mechanisms observed and quantified using optical microscopy.

  • 13.
    Varna, Janis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Persson, Magnus
    Luleå tekniska univesitet.
    Hajlane, Abdelghani
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microdamage, viscoelasticity and viscoplasticity as main phenomena in thermal stress relaxation in laminated composites2016Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 713, s. 99-102Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microdamage, viscoplastic and viscoelastic strain development in 90-layers of cross-ply laminates subjected to tensile loading is studied on unsymmetrical GF/EP laminates measuring the thermal curvature change. All three phenomena partially compensate for the effect of the thermal mismatch reducing the residual stress (specimen curvature). The viscoplastic strain contribution to curvature change is the largest whereas the effect of transient viscoelasticity is the smallest. Damage is included in the analysis through its effect on the effective transverse modulus of the 90- layer.

  • 14.
    Varna, Janis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Zhuang, Linqi
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pupurs, Andrejs
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ayadi, Zoubir
    Universite de Lorraine, Nancy.
    Growth and interaction of debonds in local clusters of fibers in unidirectional composites during transverse loading2017Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 734, s. 63-66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fiber/matrix debonding in transverse tensile loading of a unidirectional composite is analyzed calculating energy release rate (ERR) for interface crack propagation. Non-uniform fiber distribution (local hexagonal fiber clustering) is assumed in the model. The matrix region containing the central fiber with the debond and the 6 surrounding fibers is embedded in a large block of homogenized composite which has the same fiber content as the region analyzed explicitly. Some of the fibers surrounding the central fiber may also have a debond. The effect of the local clustering and of the presence of other debonds on magnification of the ERR is analyzed

  • 15.
    Xue, Peng
    et al.
    Department of Ferrous Metallurgy, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing.
    Yang, Qixing
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Liu, Guiqun
    School of Materials Science and Engineering, Beifang University of Nationalities, Yinchuan, Ningxia.
    Han, Feng Lan
    School of Materials Science & Engineering, Beifang University of Nationalities, Yinchuan, Ningxia.
    Liang, Jiang
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Engström, Fredrik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Björkman, Bo
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Mineralteknik och metallurgi.
    Air Quenching of Steel slag to Enhance its Hydraulic Activity for Recycling the Slag as Meterials in Cement and Concrete Applications2017Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 737, s. 488-493Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A steel slag has been treated by air granulation, in order to enhance cementitious properties of the slag. Two samples with sizes ranged 1.68-2.38mm and 212-297μm and coded as Slag A and Slag B, respectively, were chosen from the granulated slag for investigations. A sample of the original steel slag was also studied. XRD analyses indicated the formations of α-C2S, β-C2S, C2F, C2MS2, f-MgO and α-C2S, C2F, f-MgO in Slag A and Slag B, respectively. The phases in the two slag samples were quite different from the phases found in steel slag. The SEM results show a reduction of C2S sizes from 10-20μm for the steel slag to nano-scales by air quenching for Slag B. This treatment of air quenching has increased the cumulative heat of hydration to 105.35J/g measured for Slag B, almost two times greater than that of the steel slag. The study results demonstrate a high potential for utilizations of the steel slag in cement and concrete applications after the slag treatment by air quenching. The treatment may thus lead to an environmental friendly and cost-effective recycling for the steel slag. This can also contribute to the sustainable developments in the steel and cement/concrete industries.

  • 16.
    Zou, Zhongquan
    et al.
    Central South University of Forestry and Technology, Changsha.
    Enochsson, Ola
    He, Guojing
    Central South University of Forestry and Technology, Changsha.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Finite element analysis of small span reinforced concrete trough railway bridge2009Inngår i: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 400-402, s. 645-650Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The static behavior of a reinforced concrete trough railway bridge is analyzed by finite element method. The influences of load distribution fashion, supporting width of the bearings and the additional support beneath the girder are investigated; and the spatial effect of the stress distribution is studied as well. To confirm the analysis accuracy, the results are calibrated with the field load test results. It is found that the influence of load distribution fashion is minor and negligible, while those of supporting width and additional support are not negligible; and the spatial effect is significant.

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