The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Janis Varna - One of the best experts on this subject based on the ideXlab platform.

  • effects of voids on quasi static and tension fatigue behaviour of carbon fibre composite laminates
    Journal of Composite Materials, 2015
    Co-Authors: S M Sisodia, Fredrik Edgren, Kristofer E Gamstedt, Janis Varna
    Abstract:

    The effect of voids on quasi-isotropic carbon-fibre reinforced plastic laminates under quasi-static loading is compared with that under cyclic tension loading. Emphasis is placed on following damage development at the Non-Crimp Fabric ply-level by investigating the influence of voids on damage accumulation, most notably transverse cracking and delamination. Details from experiments include micrographs of voids taken in both scanning-electron and light microscopy, measurements of void content and crack density using light microscopy, and stiffness plots from both quasi-static and cyclic tests. The stiffness results are compared with theoretical predictions accounting for transverse cracks. Voids have a significantly more detrimental effect on the mechanical properties in cyclic loading compared with quasi-static loading. Specifically, the stiffness reduction development, the underlying transverse cracking in layers and the number of cycles to failure are affected. Quality control by only quasi-static testi...

  • effective stiffness of curved 0 layers for stiffness determination of cross ply non crimp Fabric composites
    Journal of Reinforced Plastics and Composites, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Z. Ayadi, Janis Varna
    Abstract:

    The effect of the 0°-tow waviness on axial stiffness of cross-ply Non-Crimp Fabric composites is analysed using multiscale approach. The curved 0°- and 90°-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0°-layer stiffness is calculated analysing isolated curved 0°-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0°-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0°-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties...

  • Master curve approach to axial stiffness calculation for Non-Crimp Fabric biaxial composites with out-of-plane waviness
    Composites Part B: Engineering, 2014
    Co-Authors: Hana Zrida, Erik Marklund, Z. Ayadi, Janis Varna
    Abstract:

    Abstract The effect of 0°-tow out-of-plane waviness on the biaxial Non-Crimp-Fabric (NCF) composite axial stiffness is investigated. Homogenizing, the bundle mesostructure of the NCF composite is replaced by layers. Then the composite is represented by a laminate with flat layers with effective stiffness properties representing the curved 0°-layer and the 90°-layer with varying thickness. It is shown that the NCF composite knock-down factor characterizing the stiffness degradation has almost the same dependence on wave parameters as the knock-down factor for the curved 0°-layer. Numerical analysis showed that 90°-layer knock-down factor versus amplitude curves for different wavelength can be reduced to one master curve which can be described by a one-parameter expression with the parameter dependent on the used material. This observation is used to obtain high accuracy for analytical predictions for knock-down factors for cases with different wavelength and amplitudes based on two FE calculations only.

  • the sources of inelastic behavior of glass fibre vinylester non crimp Fabric 45 s laminates
    Journal of Reinforced Plastics and Composites, 2011
    Co-Authors: Konstantinos Giannadakis, Roberts Joffe, Peter Mannberg, Janis Varna
    Abstract:

    The non-linear and time-dependent stress—strain response of NCF [±45]s laminates in tension is studied. Testing methodology is suggested to separate and quantify the effect of damage development, n...

  • damage progression in non crimp Fabric composites
    Non-Crimp Fabric Composites#R##N#Manufacturing Properties and Applications, 2011
    Co-Authors: L E Aap, Janis Varna, Erik Marklund
    Abstract:

    Abstract: In this chapter, prevailing damage mechanisms in in-plane loaded Non-Crimp Fabric (NCF) composites, as well as out-of-plane impact-loaded and subsequent in-plane compression-loaded NCF composite structures, are presented and discussed in detail. Particular emphasis is on the identification of differences and similarities in failure mechanisms for NCF composites to those in traditional tape-based composites.

Yunfei Rao - One of the best experts on this subject based on the ideXlab platform.

  • low velocity impact behavior of intralayer hybrid composites based on carbon and glass non crimp Fabric
    Composite Structures, 2020
    Co-Authors: Chen Zhang, Yunfei Rao
    Abstract:

    Abstract The low-velocity impact behavior of intralayer hybrid composite laminates made from warp-knitted Fabrics with carbon (C) and glass (G) fibers was investigated. The impact testing at varying energy levels was performed using drop weight impact tests. The impact response was evaluated in terms of peak force and absorbed energy, and damage mechanism were characterized by visual observations and fluorescent dye penetration. Furthermore, the damage modes was assessed through quasi-static indentation (QSI) and acoustic emission (AE) techniques. The results from this study indicated that the hybrid structure exhibited a positive hybrid effect in peak force and the absorbed energy, and failure mechanism were significantly affected by the hybrid ratio and intralayer structure. The intralayer hybrid laminate of C:G = 1:1 revealed better impact resistance, and that of C:G = 1:4 exhibited less damage accompanied by the least carbon fiber content, however, more fiber damage appeared in C:G = 1:2 laminates.

  • low velocity impact behavior of interlayer intralayer hybrid composites based on carbon and glass non crimp Fabric
    Materials, 2018
    Co-Authors: Chen Zhang, Yunfei Rao
    Abstract:

    Composites have gained wide use in structural applications; however, they are sensitive to impact damage. The use of hybrid composites is an effective way to overcome this deficiency. The effects of various hybrid structures of interlayer and intralayer warp-knitted Fabrics with carbon and glass fibers on the low-velocity impact behavior of composite laminates were studied. Drop-weight impact tests were conducted on two types of interlayer, sandwich and intralayer hybrid composite laminates, which were compared with homogenous composite laminates. During low-velocity impact tests, the time histories of impact forces and absorbed energy by laminate were recorded. The failure modes were analyzed using the micro-CT (computed tomography) and C-scan techniques. The results revealed that the hybrid structure played an important role in peak force and the absorbed energy, and that the hybrid interface had an influence on damage modes, whereas the intralayer hybrid composite laminate damage was affected by the impact location. The intralayer hybrid laminate with C:G = 1:1 exhibited better impact resistance compared to the other hybrid structures.

Pedro P. Camanho - One of the best experts on this subject based on the ideXlab platform.

  • a strategy to improve the structural performance of non crimp Fabric thin ply laminates
    Composite Structures, 2018
    Co-Authors: A. Arteiro, Giuseppe Catalanotti, J Xavier, Pedro P. Camanho
    Abstract:

    Abstract The enhanced mechanical performance of thin-ply laminates results from their ability to delay the onset of damage typically observed in composite materials. However, in notched structures, subcritical damage growth causes beneficial stress redistributions in the vicinity of the notch, blunting the stress concentration. Precluding these damage mechanisms, as in thin-ply laminates, may potentially lead to inferior notched responses. To obviate this limitation of thin-ply laminates, a strategy based on the combination of standard grade 0° plies and thin transverse and off-axis plies is analysed in this paper. A detailed study of the effect of 0° ply blocking is carried out, with particular emphasis on the blunting mechanisms and notched response. Tests on scaled notched panels loaded in tension, with notch sizes between 6 mm and 30 mm, show that the combination of standard grade 0° ply blocks with thin transverse and off-axis plies promotes localised fibre-matrix splitting, which acts as an important notch blunting mechanism, while preventing matrix cracking and delamination. This results in an improved notched response and superior large damage capability. It is also shown that thicker 0° ply blocks provide higher stability in composite bolted joints, while the thin transverse and off-axis plies contribute for matrix-dominated damage suppression, resulting in an improved bolt-bearing response. The improvements of the large damage capability and bolt-bearing performance are obtained without compromising the superior unnotched tensile and compressive strengths intrinsic to thin-ply laminates.

  • large damage capability of non crimp Fabric thin ply laminates
    Composites Part A-applied Science and Manufacturing, 2014
    Co-Authors: A. Arteiro, Giuseppe Catalanotti, J Xavie, Pedro P. Camanho
    Abstract:

    Abstract The residual strength of thin-ply Non-Crimp Fabric laminates with large through-the-thickness cracks is investigated in this paper. Analysis methods such as the linear elastic fracture mechanics, inherent flaw, point-stress, average-stress and Finite Fracture Mechanics are used to predict large damage capability. Experiments show that thin-ply Non-Crimp Fabric laminates exhibit high resistance to propagation of large cracks and a remarked crack-bridging effect. Due to the unsuitability of existing models to capture such bridging processes, large damage capability is systematically underestimated by the traditional analysis methods. By taking into account the R -curve of the material in the Finite Fracture Mechanics analysis good predictions of the notched response of laminated plates with large through-penetration damage are obtained using only independently measured material properties; in addition, the Finite Fracture Mechanics model does not require fitting parameters or complex finite element analyses.

  • Notched response of Non-Crimp Fabric thin-ply laminates: Analysis methods
    Composites Science and Technology, 2013
    Co-Authors: A. Arteiro, Giuseppe Catalanotti, José Xavier, Pedro P. Camanho
    Abstract:

    Analysis methods to predict the open-hole tensile and compressive response of thin-ply Non-Crimp Fabric laminates are investigated in this paper. The point- and average-stress models and the Finite Fracture Mechanics model are used. It is shown that all models predict with reasonable accuracy the observed size effects in both tension and compression. The Finite Fracture Mechanics model, which requires two material properties (the unnotched strength and the fracture toughness) and does not need calibration from a baseline specimen, is used to predict the notched response of thin-ply Non-Crimp Fabric laminates and of typical aerospace grade laminates based on unidirectional pre-impregnated plies. No substantial differences in notch sensitivity and inherent material/geometry brittleness is predicted.

  • Notched response of Non-Crimp Fabric thin-ply laminates
    Composites Science and Technology, 2013
    Co-Authors: A. Arteiro, Giuseppe Catalanotti, José Xavier, Pedro P. Camanho
    Abstract:

    Abstract This paper presents an experimental investigation of the mechanical response of a new class of advanced composite materials manufactured using thin Non-Crimp Fabrics. Tensile and compressive tests in both unnotched and notched specimens were performed using two different lay-ups. The notched tests were based on specimens with central cracks and with circular holes, loaded in tension and compression. Digital image correlation was used to monitor the onset and propagation of damage on the surface plies. The results show that the lay-up with blocked plies and with higher differences in fiber orientation angles between consecutive plies has lower unnotched strength. However, due to the larger fracture process zone observed in the notched tests, such lay-up has marginally higher notched strengths. A size effect on the strength was observed for both the open-hole tension and compression tests. The size effect and the associated notch sensitivity of thin Non-Crimp Fabrics were similar to those observed in typical aerospace grade unidirectional pre-impregnated composite materials. It is also concluded that the thin Non-Crimp Fabrics exhibit an improved response to bolt-bearing loads over traditional composite materials.

Youngbin Park - One of the best experts on this subject based on the ideXlab platform.

  • csai analysis of non crimp Fabric cross ply laminate manufactured through wet compression molding process
    Composite Structures, 2021
    Co-Authors: Sooyoung Lee, Chaeyoung Hong, Taeseong Choi, Hyegyu Kim, Soochang Kang, Youngbin Park
    Abstract:

    Abstract The main purpose of the present work is to demonstrate mechanical performance of a wet-compression-molding (WCM) composite product through conventional compressive-strength-after-impact (CSAI) analysis. Biaxial Non-Crimp Fabric (NCF) is utilized to manufacture laminated composite panels. Specimens are cut from the panels and tested to characterize fundamental mechanical properties of the NCF composite. The volume fractions of fibers and voids are also measured to evaluate the quality of the WCM product. Impact tests are carried out to examine impact resistance of the composite structure. Numerous impact characteristics at various energy levels are quantitatively measured. Internal failure patterns and damage extent are revealed via X-ray CT. Compression tests on the impacted plates are followed to evaluate structural integrity and damage tolerance (SIDT). 3D DIC technique is employed and distinct buckling responses dependent on impact energy levels are successfully visualized. Experimental results are showing a promising potential of the WCM process as one of the alternatives to the conventional autoclave-based Fabrication method.

Chen Zhang - One of the best experts on this subject based on the ideXlab platform.

  • low velocity impact behavior of intralayer hybrid composites based on carbon and glass non crimp Fabric
    Composite Structures, 2020
    Co-Authors: Chen Zhang, Yunfei Rao
    Abstract:

    Abstract The low-velocity impact behavior of intralayer hybrid composite laminates made from warp-knitted Fabrics with carbon (C) and glass (G) fibers was investigated. The impact testing at varying energy levels was performed using drop weight impact tests. The impact response was evaluated in terms of peak force and absorbed energy, and damage mechanism were characterized by visual observations and fluorescent dye penetration. Furthermore, the damage modes was assessed through quasi-static indentation (QSI) and acoustic emission (AE) techniques. The results from this study indicated that the hybrid structure exhibited a positive hybrid effect in peak force and the absorbed energy, and failure mechanism were significantly affected by the hybrid ratio and intralayer structure. The intralayer hybrid laminate of C:G = 1:1 revealed better impact resistance, and that of C:G = 1:4 exhibited less damage accompanied by the least carbon fiber content, however, more fiber damage appeared in C:G = 1:2 laminates.

  • low velocity impact behavior of interlayer intralayer hybrid composites based on carbon and glass non crimp Fabric
    Materials, 2018
    Co-Authors: Chen Zhang, Yunfei Rao
    Abstract:

    Composites have gained wide use in structural applications; however, they are sensitive to impact damage. The use of hybrid composites is an effective way to overcome this deficiency. The effects of various hybrid structures of interlayer and intralayer warp-knitted Fabrics with carbon and glass fibers on the low-velocity impact behavior of composite laminates were studied. Drop-weight impact tests were conducted on two types of interlayer, sandwich and intralayer hybrid composite laminates, which were compared with homogenous composite laminates. During low-velocity impact tests, the time histories of impact forces and absorbed energy by laminate were recorded. The failure modes were analyzed using the micro-CT (computed tomography) and C-scan techniques. The results revealed that the hybrid structure played an important role in peak force and the absorbed energy, and that the hybrid interface had an influence on damage modes, whereas the intralayer hybrid composite laminate damage was affected by the impact location. The intralayer hybrid laminate with C:G = 1:1 exhibited better impact resistance compared to the other hybrid structures.