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Rinze Benedictus - One of the best experts on this subject based on the ideXlab platform.

  • Mode I Quasi-Static Delamination Growth in Multidirectional Composite Laminates with Different Thicknesses
    2016
    Co-Authors: Yi Sun, R.c. Alderliesten Liaojun Yao, Rinze Benedictus
    Abstract:

    Multidirectional DCB specimens with different thicknesses were manufactured and tested to have in-depth understanding of Delamination behavior in composite laminates. The initiation crack Growth is demonstrated to be ply orientation and thickness independent. However, interlaminar resistance and damage mechanisms in Delamination Growth are significantly related to the interface configuration as well as thickness. Fractography analysis demonstrated that resistance difference between unidirectional and multidirectional DCB specimens is related to damage mechanisms. Optical microscope observation revealed that crack path in the multidirectional specimens is zigzag. This phenomenon becomes vague with thickness increase. The appearance of zigzag crack indicates both interlaminar and intralaminar damage can occur in the Delamination Growth. However, interlaminar damage becomes the dominant failure mode in the thick specimens. SEM (Scanning Electron Microscope) observation demonstrated fibre prints and cusps are two typical morphologies located on the fracture surface. These features are even more significant in the multidirectional interface with thickness decrease. This paper will conclude that interface configuration and specimen thickness have significant effects on the damage mechanisms and interlaminar resistance during Delamination Growth in composite laminates. It is, therefore, insufficient to apply the unidirectional DCB specimen with a given thickness to determine Delamination Growth and damage mechanisms of a composite material.

  • Fatigue Delamination Growth Behavior in Composite Materials under Block Loading
    2016
    Co-Authors: Liaojun Yao, R.c. Alderliesten Yi Sun, Rinze Benedictus
    Abstract:

    Delamination is one of the most important damage in composite materials. It can propagate under fatigue loading and cause failures of composite structures. With the application of damage tolerance design philosophy in engineering and requirement of light weight structures in advanced aircrafts, how to characterize fatigue Delamination Growth behavior in composite materials and develop reliable prediction models become critical issues for the application of these materials. A large amount of studies have been conducted on the characterization of fatigue Delamination Growth under constant amplitude loading in composite materials. However, little attention has ever been put into the block loading sequence effect on Delamination Growth. Referring to fatigue crack Growth in metals, shielding mechanism of plasticity deformation around the crack front plays a dominant role in the loading sequence effect. Fibre bridging, acting as the shielding mechanism, therefore can contribute to the loading sequence effect on fatigue Delamination Growth in composite materials. Double Cantilever Beam (DCB) specimens were designed and manufactured for the mode I fatigue Delamination tests with HI-HI and LO-HI block loading sequences. Paris relation was subsequently used to interpret the experimental results. It demonstrates there is an obvious loading sequence effect on fatigue Delamination Growth in composite materials. The fatigue crack Growth in the HI-HI block loading is slower than it in the LO-HI block loading.

  • effect of stress ratio or mean stress on fatigue Delamination Growth in composites critical review
    Composite Structures, 2015
    Co-Authors: Rafiullah Khan, René Alderliesten, Saeed Badshah, Rinze Benedictus
    Abstract:

    Abstract The studies reported in the literature on the effect of stress ratio or mean stress on fatigue Delamination Growth in composites are critically reviewed in this paper. These studies are classified according to their mode of fracture. Majority of the studies lack a mechanistic approach to the Delamination Growth characterization and the effect of stress ratio. The researchers are divided in the use of a unified correlating parameter for the Delamination Growth. The mechanisms of fatigue crack Growth in metals are often extended to the Delamination Growth characterization.

  • Two-parameter model for Delamination Growth under mode I fatigue loading (Part A: Experimental study)
    Composites Part A: Applied Science and Manufacturing, 2014
    Co-Authors: Rafiullah Khan, René Alderliesten, Rinze Benedictus
    Abstract:

    Abstract Mode I Delamination Growth under fatigue loading has been experimentally investigated in carbon/epoxy laminates. The experimental results are used in Part B of this paper for the development of a two-parameter mechanistic model for Delamination Growth. Fatigue tests are performed using double cantilever beam and width tapered double cantilever beam specimens. Delamination Growth has been characterized using strain energy release rate approach. Fracture surfaces have been investigated for the effect of stress ratio and monotonic and cyclic load using scanning electron microscopy. The results show that microscopic features depend on monotonic and cyclic load.

  • Two-parameter model for Delamination Growth under mode I fatigue loading (Part B: Model development)
    Composites Part A: Applied Science and Manufacturing, 2014
    Co-Authors: Rafiullah Khan, René Alderliesten, Rinze Benedictus
    Abstract:

    Abstract A two-parameter model for mode I fatigue Delamination Growth has been developed and is presented in this paper. The model is based on the mechanisms of decohesion that was determined through SEM investigations. The experimental data of fatigue Delamination Growth under mode I fatigue from the current study and the literature has been used for the validation of the model.

Leif Asp - One of the best experts on this subject based on the ideXlab platform.

  • Mixed-mode Delamination Growth in carbon-fibre composite laminates under cyclic loading
    International Journal of Solids and Structures, 2004
    Co-Authors: N. Blanco, Erik Kristofer Gamstedt, Leif Asp, J. Costa
    Abstract:

    Delamination Growth under fatigue loads in real composite components generally develops in a non-constant propagation mode. The aim of the investigation described in this article was to develop a m ...

  • effects of temperature on Delamination Growth in a carbon epoxy composite under fatigue loading
    International Journal of Fatigue, 2002
    Co-Authors: A. Sjögren, Leif Asp
    Abstract:

    Abstract This paper presents a study of Delamination Growth in HTA/6376C carbon fibre/epoxy laminates. Tests were conducted under Mode I, Mode II and mixed-mode static and fatigue loading at both ambient conditions and elevated temperature. The results show that the strain energy release rate threshold values for Delamination Growth under fatigue loading are significantly lower than the critical energy release rates in static tests. At elevated temperature, the threshold values in the fatigue loading were only about 10% of the critical values in the static tests. A fractographic analysis of the Delamination Growth revealed that the fracture surfaces generated at elevated temperature generally were similar to the fracture surfaces generated at room temperature. Nevertheless, some differences in morphology of the fracture surfaces were observed, and their effect on the static and fatigue Delamination Growth is discussed in detail.

  • Effects of temperature on Delamination Growth in a carbon/epoxy composite under fatigue loading
    International Journal of Fatigue, 2002
    Co-Authors: A. Sjögren, Leif Asp
    Abstract:

    Abstract This paper presents a study of Delamination Growth in HTA/6376C carbon fibre/epoxy laminates. Tests were conducted under Mode I, Mode II and mixed-mode static and fatigue loading at both ambient conditions and elevated temperature. The results show that the strain energy release rate threshold values for Delamination Growth under fatigue loading are significantly lower than the critical energy release rates in static tests. At elevated temperature, the threshold values in the fatigue loading were only about 10% of the critical values in the static tests. A fractographic analysis of the Delamination Growth revealed that the fracture surfaces generated at elevated temperature generally were similar to the fracture surfaces generated at room temperature. Nevertheless, some differences in morphology of the fracture surfaces were observed, and their effect on the static and fatigue Delamination Growth is discussed in detail.

  • On transition of Delamination Growth behaviour for compression loaded composite panels
    International Journal of Solids and Structures, 2001
    Co-Authors: K.-f. Nilsson, Leif Asp, A. Sjögren
    Abstract:

    This paper presents a combined numerical and experimental study of slender composite panels loaded in compression with artificial Delaminations at two different depths. The study was motivated by finite element analyses where this change in Delamination depth induced a transition in the direction of Delamination Growth along with a change in the basic fracture modes and stability. Tests were then carried out to verify the transition in Delamination Growth. The predicted transitions were to a large extent also seen in the tests. The paper gives an outline of the computational model, which includes contact between delaminated members, calculation of energy release rate with fracture mode separation by an approximate as well as a reliable method for general layups, and moving mesh scheme to account for Delamination Growth. The experimental work includes monitoring of Delamination Growth by C-scan and acoustic emission along with a detailed fractographical study. The correlation between experimental observations and computed results are discussed in detail.

  • Delamination Growth and thresholds in a carbon epoxy composite under fatigue loading
    Journal of Composites Technology & Research, 2001
    Co-Authors: Leif Asp, A. Sjögren, Emile S. Greenhalgh
    Abstract:

    This paper presents a study on Delamination Growth in Mode I, Mode II and mixed mode under fatigue loading in an HTA/6376C composite. The computed slopes of the modified Paris plots were high. Therefore, threshold values of the strain energy release rate for Delamination Growth were determined. Low fatigue threshold values revealed a significant effect of fatigue loading. The largest effect was found for the ENF test (Mode II) for which the fatigue threshold value was only 10% of the critical strain energy release rate in static tests. Threshold values for MMB (mixed mode) and DCB (Mode I) tests were 15% and 23% of the static values, respectively. Fractographic evaluation revealed identical initial failure mechanisms in fatigue and static loading conditions for the ENF specimen. The ENF specimen failed by formation and coalescence of microcracks. The low fatigue threshold for the ENF specimen was explained by microscopical observations on the specimen edge. It was also shown that the fracture surfaces generated in static and fatigue DCB and MMB tests were similar.

A. Sjögren - One of the best experts on this subject based on the ideXlab platform.

  • effects of temperature on Delamination Growth in a carbon epoxy composite under fatigue loading
    International Journal of Fatigue, 2002
    Co-Authors: A. Sjögren, Leif Asp
    Abstract:

    Abstract This paper presents a study of Delamination Growth in HTA/6376C carbon fibre/epoxy laminates. Tests were conducted under Mode I, Mode II and mixed-mode static and fatigue loading at both ambient conditions and elevated temperature. The results show that the strain energy release rate threshold values for Delamination Growth under fatigue loading are significantly lower than the critical energy release rates in static tests. At elevated temperature, the threshold values in the fatigue loading were only about 10% of the critical values in the static tests. A fractographic analysis of the Delamination Growth revealed that the fracture surfaces generated at elevated temperature generally were similar to the fracture surfaces generated at room temperature. Nevertheless, some differences in morphology of the fracture surfaces were observed, and their effect on the static and fatigue Delamination Growth is discussed in detail.

  • Effects of temperature on Delamination Growth in a carbon/epoxy composite under fatigue loading
    International Journal of Fatigue, 2002
    Co-Authors: A. Sjögren, Leif Asp
    Abstract:

    Abstract This paper presents a study of Delamination Growth in HTA/6376C carbon fibre/epoxy laminates. Tests were conducted under Mode I, Mode II and mixed-mode static and fatigue loading at both ambient conditions and elevated temperature. The results show that the strain energy release rate threshold values for Delamination Growth under fatigue loading are significantly lower than the critical energy release rates in static tests. At elevated temperature, the threshold values in the fatigue loading were only about 10% of the critical values in the static tests. A fractographic analysis of the Delamination Growth revealed that the fracture surfaces generated at elevated temperature generally were similar to the fracture surfaces generated at room temperature. Nevertheless, some differences in morphology of the fracture surfaces were observed, and their effect on the static and fatigue Delamination Growth is discussed in detail.

  • On transition of Delamination Growth behaviour for compression loaded composite panels
    International Journal of Solids and Structures, 2001
    Co-Authors: K.-f. Nilsson, Leif Asp, A. Sjögren
    Abstract:

    This paper presents a combined numerical and experimental study of slender composite panels loaded in compression with artificial Delaminations at two different depths. The study was motivated by finite element analyses where this change in Delamination depth induced a transition in the direction of Delamination Growth along with a change in the basic fracture modes and stability. Tests were then carried out to verify the transition in Delamination Growth. The predicted transitions were to a large extent also seen in the tests. The paper gives an outline of the computational model, which includes contact between delaminated members, calculation of energy release rate with fracture mode separation by an approximate as well as a reliable method for general layups, and moving mesh scheme to account for Delamination Growth. The experimental work includes monitoring of Delamination Growth by C-scan and acoustic emission along with a detailed fractographical study. The correlation between experimental observations and computed results are discussed in detail.

  • Delamination Growth and thresholds in a carbon epoxy composite under fatigue loading
    Journal of Composites Technology & Research, 2001
    Co-Authors: Leif Asp, A. Sjögren, Emile S. Greenhalgh
    Abstract:

    This paper presents a study on Delamination Growth in Mode I, Mode II and mixed mode under fatigue loading in an HTA/6376C composite. The computed slopes of the modified Paris plots were high. Therefore, threshold values of the strain energy release rate for Delamination Growth were determined. Low fatigue threshold values revealed a significant effect of fatigue loading. The largest effect was found for the ENF test (Mode II) for which the fatigue threshold value was only 10% of the critical strain energy release rate in static tests. Threshold values for MMB (mixed mode) and DCB (Mode I) tests were 15% and 23% of the static values, respectively. Fractographic evaluation revealed identical initial failure mechanisms in fatigue and static loading conditions for the ENF specimen. The ENF specimen failed by formation and coalescence of microcracks. The low fatigue threshold for the ENF specimen was explained by microscopical observations on the specimen edge. It was also shown that the fracture surfaces generated in static and fatigue DCB and MMB tests were similar.

  • Delamination Growth and Thresholds in a Carbon/Epoxy Composite under Fatigue Loading
    Journal of Composites Technology and Research, 2001
    Co-Authors: Leif Asp, A. Sjögren, Emile S. Greenhalgh
    Abstract:

    This paper presents a study on Delamination Growth in Mode I, Mode II and mixed mode under fatigue loading in an HTA/6376C composite. The computed slopes of the modified Paris plots were high. Therefore, threshold values of the strain energy release rate for Delamination Growth were determined. Low fatigue threshold values revealed a significant effect of fatigue loading. The largest effect was found for the ENF test (Mode II) for which the fatigue threshold value was only 10% of the critical strain energy release rate in static tests. Threshold values for MMB (mixed mode) and DCB (Mode I) tests were 15% and 23% of the static values, respectively. Fractographic evaluation revealed identical initial failure mechanisms in fatigue and static loading conditions for the ENF specimen. The ENF specimen failed by formation and coalescence of microcracks. The low fatigue threshold for the ENF specimen was explained by microscopical observations on the specimen edge. It was also shown that the fracture surfaces generated in static and fatigue DCB and MMB tests were similar.

Rafiullah Khan - One of the best experts on this subject based on the ideXlab platform.

  • CRACK CLOSURE AND FIBRE BRIDGING CONTRIBUTION IN THE STRESSRATIO EFFECT ON Delamination Growth UNDER FATIGUE
    Journal of Engineering and Applied Sciences, 2017
    Co-Authors: Rafiullah Khan, Saeed Badshah, Sakhi Jan, Muhammad Amjad, Sajjad Ahmad
    Abstract:

    The objective of this paper is to investigate the contribution/role of the crack closure and the fibre bridging effects in stress-ratio influence in mode I Delamination Growth in carbon/epoxy composite laminates. The crack closure effect has been assessed by the identification of the non-linearity in the compliance curve of the double cantilever test specimen after the Delamination extension. The effect of fibre bridging was investigated by cutting the bridging fibres during fatigue Delamination. The fatigue test data was process using fracture mechanics principles. The Delamination Growth rate in laminates was characterized using approach of strain energy release rate. The results of the experiments of fatigue Delamination Growth with bridging fibres and un-bridged fibres have been compared for different fatigue stress-ratios. The results show that crack closure only occurs at lower stress ratios. Fibre bridging does not affect the stress ratio however the crack rate was decreased in this case.

  • effect of stress ratio or mean stress on fatigue Delamination Growth in composites critical review
    Composite Structures, 2015
    Co-Authors: Rafiullah Khan, René Alderliesten, Saeed Badshah, Rinze Benedictus
    Abstract:

    Abstract The studies reported in the literature on the effect of stress ratio or mean stress on fatigue Delamination Growth in composites are critically reviewed in this paper. These studies are classified according to their mode of fracture. Majority of the studies lack a mechanistic approach to the Delamination Growth characterization and the effect of stress ratio. The researchers are divided in the use of a unified correlating parameter for the Delamination Growth. The mechanisms of fatigue crack Growth in metals are often extended to the Delamination Growth characterization.

  • Two-parameter model for Delamination Growth under mode I fatigue loading (Part A: Experimental study)
    Composites Part A: Applied Science and Manufacturing, 2014
    Co-Authors: Rafiullah Khan, René Alderliesten, Rinze Benedictus
    Abstract:

    Abstract Mode I Delamination Growth under fatigue loading has been experimentally investigated in carbon/epoxy laminates. The experimental results are used in Part B of this paper for the development of a two-parameter mechanistic model for Delamination Growth. Fatigue tests are performed using double cantilever beam and width tapered double cantilever beam specimens. Delamination Growth has been characterized using strain energy release rate approach. Fracture surfaces have been investigated for the effect of stress ratio and monotonic and cyclic load using scanning electron microscopy. The results show that microscopic features depend on monotonic and cyclic load.

  • Two-parameter model for Delamination Growth under mode I fatigue loading (Part B: Model development)
    Composites Part A: Applied Science and Manufacturing, 2014
    Co-Authors: Rafiullah Khan, René Alderliesten, Rinze Benedictus
    Abstract:

    Abstract A two-parameter model for mode I fatigue Delamination Growth has been developed and is presented in this paper. The model is based on the mechanisms of decohesion that was determined through SEM investigations. The experimental data of fatigue Delamination Growth under mode I fatigue from the current study and the literature has been used for the validation of the model.

  • Delamination Growth in Composites under Fatigue Loading
    2013
    Co-Authors: Rafiullah Khan
    Abstract:

    Fiber reinforced composites are attractive for aerospace applications due to high specific strength and stiffness. Their use has been gradually increased to 50% by weight of the aircraft over past decades. As a consequence, modern aircraft utilize composites in the primary structures like wing skin and fuselage. The use of composites in primary structures has increased the need for reliable strength assessment methodologies. Composites are inherent to various damage types of which Delamination is the most severe type of damage. Delaminations may grow due to fatigue resulting in the stress redistribution and potentially leading to structural failure, thus making fatigue an important design concern. Damage tolerance of aircraft structures is a key aspect in maintenance and safety of aircraft. For damage tolerant design of structures, the development of accurate Delamination Growth assessment tools is necessary. Delamination Growth is affected by both cyclic and monotonic part of the fatigue load cycle. The effect of monotonic part is known as stress ratio (ratio of minimum to maximum cyclic stress) effect on Delamination Growth, and it has been extensively studied in the literature. Chapter 2 provides a detailed review of the literature concerning the stress ratio effect on Delamination Growth. The literature review shows that previous studies empirically relate Delamination Growth to a driving force parameter that seems not based on physical mechanisms. Studies are present where mechanisms of Delamination Growth have been investigated; however there is a lack of efforts to link these quantitatively to Delamination Growth models. The objective of this thesis is the development of a mechanistic model for Delamination Growth that is based on the observed Delamination mechanisms and the effects of monotonic and cyclic loadings in fatigue. The thesis is based on the hypothesis that both monotonic and cyclic loading affect fracture surface formation, which can be used for Delamination Growth characterization. The secondary objective of the thesis is the characterization of fracture surfaces for the effect of monotonic and cyclic loading. To limit the scope, Delamination Growth under mode I fatigue has been investigated in the thesis. The approach of the thesis is experimental. Delamination Growth is characterized experimentally both on macroscopic and microscopic levels, as described in chapter 3. Fatigue tests were performed on double cantilever beam (DCB) specimens to investigate Delamination Growth behavior under different stress ratios. Specimens were made from cured laminates of M30SC/DT120 carbon/epoxy prepregs. Crack closure during Delamination Growth was investigated using a clip gauge extensometer. The effect of fiber bridging was investigated by cutting bridging fibers during Delamination Growth experiments. Microscopy of the fracture surfaces was performed using scanning electron microscopy. Width tapered DCB (WTDCB) specimens were used for the Delamination Growth tests under fatigue with constant monotonic and cyclic load during Delamination extension. Results of the fatigue tests and microscopy are presented in chapter 4. The Delamination Growth rate has been related to the strain energy release rate (SERR). The SERR range has been defined such that it resembles the correct analogous to the stress intensity factor (SIF) range. For constant SERR range, the Delamination Growth rate is higher for higher stress ratios. Crack closure was observed to occur for the lowest stress ratio applied in the tests. Fractographic analysis of the fracture surfaces revealed broken fibers, loose fibers, hackles and striations. The striations and hackles on the fracture surfaces of WTDCB specimens were quantitatively analyzed for different combinations of monotonic load and cyclic load amplitudes. It was observed that striation spacing increased with monotonic and cyclic load. The hackle length increased with monotonic load, but decreased with the cyclic load amplitude. Crack closure and fiber bridging marginally explain the stress ratio effect on Delamination Growth, as discussed in chapter 5. Crack closure increases the effective minimum load at crack tip at the lower stress ratio only. This results in higher effective stress ratio at the crack tip. In this case, the SERR range was corrected for crack closure. By plotting Delamination Growth rate against corrected SERR range, the data shifted to the region with higher stress ratios. To illustrate the effect of crack closure in 3D representation, Delamination Growth rate was plotted against SERR range and maximum SERR. It was observed that the data corrected for crack closure shifted to the higher stress ratio region, while remaining on the same crack resistance surface. It was further observed that fiber bridging decreases the Delamination Growth rate. The stress ratio remains the same. It was observed that fiber bridging affects both minimum and maximum loads during fatigue resulting in same stress ratio as without fiber bridging. In a 3D representation of Delamination Growth rate versus SERR range and maximum SERR, the data was observed to shift to the lower Delamination Growth rate region due to fiber bridging. The experimental results showed that Delamination Growth is not a unique function of SERR range, but also depend on the stress ratio. This implies that Delamination Growth depends on both cyclic and monotonic loads. A two parameter model for Delamination Growth was developed based on the observation of the effect of cyclic and monotonic load on the fracture surfaces. Chapter 6 describes the mechanism of Delamination Growth and the development of the mechanistic two parameter model for Delamination Growth prediction. The two parameter components in the model are superimposed rather than multiplied in agreement with the superposition of the effects of cyclic and monotonic loads observed with microscopic features on the fracture surfaces. The two parameter model for Delamination Growth represents a crack resistance surface for the material in the 3D coordinates of Delamination Growth rate versus SERR range and maximum SERR. The model has been implemented using data from the Delamination Growth experiments. The surface fitting tool of the commercial software MATLAB was used to obtain the equation. To validate the model, experimental data was taken from the literature. The predictions with the model and the reported experimental observations were observed to be in good agreement. The current model is different from previous models in that the relation between Delamination Growth and correlating parameters is no longer a simple fit of the experimental data by regression. The fit is rather an educated fit based on the observed contribution of monotonic and cyclic load components on fracture mechanisms. The two parameters in the model are superimposed to describe contribution of the load components. In previous two parameter models the terms were multiplied without justification using the physics of Delamination Growth. The conclusions of the thesis are summarized in chapter 8. It can be concluded that the effect of monotonic load on Delamination Growth is not fully explained by crack closure and fiber bridging. The Delamination Growth should be characterized using both monotonic and cyclic load components. These load components affects Delamination Growth at microscopic level independent of one another. The two parameter terms in the model are added in conjunction to the superposition of the effects of these parameters on microscopic features. It is concluded that the model can be extended to the Delamination Growth in different modes of fracture.

René Alderliesten - One of the best experts on this subject based on the ideXlab platform.