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عنوان فارسی مقاله:
اثر بریجینگ مقیاس بزرگ در فرسودگی بار تحت کنترل لایه لایه نمونه کربن اپوکسی بدون جهت
عنوان انگلیسی مقاله:
Effects of large scale bridging in load controlled fatigue delamination of unidirectional carbon-epoxy specimens
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Delamination under fatigue loads is widely recognized as a critical failure mode of fiber-reinforced laminates. Significant progress has been achieved on this matter over the past few decades as recently reviewed in Ref. [1]. In particular, a wealth of literature exists on modeling and experimentation of fatigue delamination based on the fracture mechanics concepts [1e6]. Yet, a thorough characterization of governing mechanisms on delamination growth under cyclic loading is still lacking. Moreover, the standardized experimental methods for characterization of fatigue delamination, such as ASTM D6115, are limited only to the onset of delamination. These limitations are primarily due to the complexity of damage events that take place in the wake of the crack during delamination growth. An important damage mechanism that can accompany fatigue delamination propagation in fibrous laminates is crack bridging by intact fibers. Bridging fibers effectively reduce the stress level at the vicinity of the crack tip and consequently contribute to crack growth resistance: under fatigue loads, development of the bridging zone affects the rate of crack growth and can lead to crack deceleration and even crack arrest. Hence, assessment of bridging effects is of particular importance in the characterization of fatigue delamination in composite laminates. In the literature, several semi-empirical relationships between the cyclic loading parameters and delamination growth rate are proposed. These models often employ a Paris-Erdogan relation between the rate of crack growth and applied cyclic energy release rate (ERR) or stress intensity factor [1]. However, the applicability of such relations is often limited to the experimental conditions in which they are established. Moreover, such an approach cannot predict crack growth deceleration while the total applied ERR increases. In contemporary approaches, bridging effects are described by a distribution of tractions over the crack faces. The relationship between the bridging tractions and corresponding crack opening displacements (COD), called traction separation relation, can serve in computational methods to model delamination [4,7e9]. A direct experimental assessment of crack-bridging tractions in fatigue delamination is, however, a challenging task, as it requires precise local measurements of strains or displacements along the bridging zone under alternating loads. As a consequence, the modeling efforts accounting for bridging do not always rely on such localmeasurements and for convenience bridging tractions are often estimated from the global response of the specimen [10e12]. Yet, distribution and intensity of bridging in fatigue delamination may differ from bridging in monotonic delamination fracture [13e15]. Moreover, when large scale bridging (LSB) prevails, it can be influenced by the laminate geometry [7,16e18]. In these studies, identification of traction-separation relations is based on COD measurement at the notch root [7] or distributed strains along the bridging zone under monotonic loads [13,16,17]. Here, the latter method [13] is adopted to identify the bridging traction contribution in fatigue fracture of carbon-epoxy composite specimens, due to its ease of implementation and data acquisition as well as versatility especially in fatigue tests: it is based on distributed strain measurements, with wavelength multiplexed fiber Bragg grating (FBG) sensors, along the crack propagation direction and subsequent inverse identification of bridging tractions using parametric finite element (FE) modeling. Employing such an approach in the analysis of monotonic fracture it is demonstrated that both the bridging zone length and steady state ERR significantly increase by increasing the specimen thickness while the crack initiation ERR, as well as the maximum bridging traction at the crack tip, are independent of the specimen geometry [16,17]. A recent micromechanical analysis of LSB supports the specimen thickness dependence of bridging during fracture [19]. Although progress has been reported on understanding bridging phenomena, studies on load-controlled fatigue delamination are very scarce. Thus, in this work, LSB effects and the specimen thickness dependence in fatigue delamination are investigated. Unidirectional carbon epoxy specimens of different thicknesses, equipped with arrays of multiplexed FBGs, are subjected to mode I force-controlled fatigue loads. Measured strain data with FBG sensors are employed to identify the bridging tractions and subsequently quantify the crack tip ERR as well as the ERR due to bridging. The results allow elucidating bridging effects in delamination growth.
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کلمات کلیدی:
Accelerated fatigue properties of unidirectional carbon/epoxy ... onlinelibrary.wiley.com/doi/10.1002/pc.20181/abstract by HS Chen - 2006 - Cited by 10 - Related articles Feb 22, 2006 - Abstract. It has been confirmed that polymer matrix composites possess viscoelastic behavior. This means that one could accelerate the fatigue ... [PDF]Fatigue Behavior of Unidirectional Carbon/Epoxy AFP Laminates ... mech.utah.edu/ASC2016/assets/1003.pdf conducted on unidirectional carbon/epoxy laminates containing gaps and the behavior ... Monitoring of damage evolution during fatigue tests was performed using infrared ... greatly reduced by introducing the delamination inside the laminate. Healing of fatigue delamination cracks in carbon–epoxy composite ... journals.sagepub.com/doi/abs/10.1177/1045389X13505005 by K Pingkarawat - 2014 - Cited by 9 - Related articles (2009) Fatigue delamination behaviour of unidirectional carbon fibre/epoxy laminates reinforced by Z-Fiber® pinning. Engineering Fracture Mechanics 76: ... Composite Structures 2 - Page 19 - Google Books Result https://books.google.com/books?isbn=9400966407 I.H. Marshall - 2012 - Technology & Engineering DE CHARENTENAY, F. X., KAMIMURA, K, and LEMASCON, A., Fatigue delamination in unidirectional carbon-epoxy composites, Materials, Experimentation ... Mechanics of Nondestructive Testing - Page 401 - Google Books Result https://books.google.com/books?isbn=1468438573 Stinchcomb - 2012 - Technology & Engineering CONCLUSION In this study of fatigue delamination in unidirectional Carbon-Epoxy we have shown that the NDT contributions to the results were decisive. Design, Manufacturing and Applications of Composites: Proceedings of ... https://books.google.com/books?isbn=1605950289 Anh Dung Ngo - 2010 - Composite materials Similarly, most published fatigue delamination growth studies were performed ... was a unidirectional carbon fiber reinforced epoxy prepreg, G40-800/5276-1, ... Design, Manufacturing and Applications of Composites Tenth Workshop ... https://books.google.com/books?isbn=1605951692 Reza Vaziri, Asemi Nakai, Bryn Crawford - 2015 - Technology & Engineering ... Mode II Fatigue Delamination Growth in an Aerospace Grade Carbon/Epoxy ... Delamination Fracture Toughness of Unidirectional Glass/Epoxy Composites ...
