Part A: applied scienc and manufacturing ELSEVIER Composites: Part A 30(1999)521-524 Crack deflection in ceramic composites and fiber coating design criteria Ronald J. Kerans", Triplicane A. Parthasarathy Air Force Research Laboratory, Materials and Manufacturing Directorate(WLMLLN), Wright-Patterson AFB, OH 45433-7817, USA Abstract It is widely understood that the remarkable toughnesses demonstrated by some ceramic composites are dependent upon deflection of matrix cracks into fiber/matrix interfacial cracks. Carbon and Bn fiber coatings are ideally suited for promotion of such crack deflection, but have the unfortunate weakness of limited oxidation resistance. The rational design of oxidation-resistant altermative fiber coatings is facilitated by consideration of the details of crack deflection, growth of interfacial cracks, and subsequent sliding along the interfacial crack surface. This work discusses some of these details and the implications regarding the design and testing of alternative fiber coating systems. c 1999 Elsevier Science Ltd. All rights reserved Keywords: Composites interfaces; Fiber coatings; B Debonding: Crack deflection 1. Introduction 2. Coating toughness requirements In the earliest and many subsequent ceramic composites, Experience with successful composites and theoretical fiber/matrix interfacial layers, serendipitously formed by treatments have led to the prevalent assumption that good degradation of the fiber, were sufficiently weak that they composite behavior requires that the debond crack tough- fractured under the influence of approaching matrix cracks ness and friction should both be quite low(see, for example, thereby protecting the fibers from the stress concentration of [5]). Reports of substantially improved properties of NICA- the matrix crack(see, for example, [1D). The resulting brid- LoN /C/SiC composites resulting from the sole processing ging and debonding behavior resulted in the ability to change of pre-treating the surface of the fiber [6, 7] have accommodate cracking and still carry load, thereby provid- motivated reexamination of these assumptions regarding ing relaxation and load transfer from over-stressed regions he upper limits of allowable values The behavior of the composite to less loaded regions[2] It is this yielding of the materials is not fundamentally different, but is suffi type of mechanism that provides high toughness; however application of such composites has been limited primarily as that they suggest new possibilities for interface coating a result of environmental degradation of the interfacial properties. Recent preliminary work using rough interface layer. It has become widely appreciated that the develop- formalism(see section below) to analyze pushout tests on ment of robust resistance to environmental degradation these composites [11] may provide a revision of the the major requirement to enable exploitation of the many perceived requirements and is summarized in this section desirable characteristics of ceramic composites [3]. This Both systems consist of pyrolytic carbon-coated ceramic equirement has inspired research into oxide coatings that grade NICaLoN fibers in a matrix of CVI SiC. In one will promote crack deflection [4]. Oxidation-resistant case, the fibers were subjected to a proprietary treatment to substitutes will differ in many ways from C and Bn. reduce oxygen levels at the surface of the fiber[8, 9].The Successful application of them will likely require a much composites made with treated fibers demonstrate more complex engineering of the coatings themselves and higher strength at the same strain-to-failure, much the overall composite system to obtain comparable results. matrix crack spacing and significantly different This will require an explicit appreciation of the details of the stress-strain behavior [6] crack deflection and sliding processe Unusual fiber pushout behavior of the high strength mate- rial has been analyzed using the rough interface formalism and a rather complex failure scenario. Perhaps the most important outcome of the work is the suggestion that the Corresponding author Fax: + 1-937-255-3007 fracture energy for debonding can be higher than often 1359-835X/99/S-see front matter O 1999 Elsevier Science Ltd. All rights reserved P:S1359-835X(98)00144-4
Crack deflection in ceramic composites and fiber coating design criteria Ronald J. Kerans*, Triplicane A. Parthasarathy Air Force Research Laboratory, Materials and Manufacturing Directorate (WL/MLLN), Wright-Patterson AFB, OH 45433-7817, USA Abstract It is widely understood that the remarkable toughnesses demonstrated by some ceramic composites are dependent upon deflection of matrix cracks into fiber/matrix interfacial cracks. Carbon and BN fiber coatings are ideally suited for promotion of such crack deflection, but have the unfortunate weakness of limited oxidation resistance. The rational design of oxidation-resistant alternative fiber coatings is facilitated by consideration of the details of crack deflection, growth of interfacial cracks, and subsequent sliding along the interfacial crack surface. This work discusses some of these details and the implications regarding the design and testing of alternative fiber coating systems. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: Composites interfaces; Fiber coatings; B. Debonding; Crack deflection 1. Introduction In the earliest and many subsequent ceramic composites, fiber/matrix interfacial layers, serendipitously formed by degradation of the fiber, were sufficiently weak that they fractured under the influence of approaching matrix cracks thereby protecting the fibers from the stress concentration of the matrix crack (see, for example, [1]). The resulting bridging and debonding behavior resulted in the ability to accommodate cracking and still carry load, thereby providing relaxation and load transfer from over-stressed regions of the composite to less loaded regions [2]. It is this yielding type of mechanism that provides high toughness; however, application of such composites has been limited primarily as a result of environmental degradation of the interfacial layer. It has become widely appreciated that the development of robust resistance to environmental degradation is the major requirement to enable exploitation of the many desirable characteristics of ceramic composites [3]. This requirement has inspired research into oxide coatings that will promote crack deflection [4]. Oxidation-resistant substitutes will differ in many ways from C and BN. Successful application of them will likely require a much more complex engineering of the coatings themselves and the overall composite system to obtain comparable results. This will require an explicit appreciation of the details of the crack deflection and sliding processes. 2. Coating toughness requirements Experience with successful composites and theoretical treatments have led to the prevalent assumption that good composite behavior requires that the debond crack toughness and friction should both be quite low (see, for example, [5]). Reports of substantially improved properties of NICALONe/C/SiC composites resulting from the sole processing change of pre-treating the surface of the fiber [6,7] have motivated reexamination of these assumptions regarding the upper limits of allowable values [8–10]. The behavior of the materials is not fundamentally different, but is suffi- ciently outside the assumed envelope of workable properties that they suggest new possibilities for interface coating properties. Recent preliminary work using rough interface formalism (see section below) to analyze pushout tests on these composites [11] may provide a revision of the perceived requirements and is summarized in this section. Both systems consist of pyrolytic carbon-coated ceramic grade NICALONe fibers in a matrix of CVI SiC. In one case, the fibers were subjected to a proprietary treatment to reduce oxygen levels at the surface of the fiber [8,9]. The composites made with treated fibers demonstrate 30% higher strength at the same strain-to-failure, much finer matrix crack spacing and significantly different tensile stress–strain behavior [6]. Unusual fiber pushout behavior of the high strength material has been analyzed using the rough interface formalism and a rather complex failure scenario. Perhaps the most important outcome of the work is the suggestion that the fracture energy for debonding can be higher than often Composites: Part A 30 (1999) 521–524 1359-835X/99/$ – see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-835X(98)00144-4 * Corresponding author. Fax: 1 1-937-255-3007
R.J. Kerans, T.A. Parthasarathy /Composites. ParT 4 30(1999)521-524 assumed and still perform the necessary function of crack sequence [19]. Since the microscopic details of fracture deflection. This result suggests that the window of proper- are difficult to probe experimentally, the exact sequence ties that can be possessed by an oxide alternative coating, of events in real fibrous composites has remained a matter for example, is larger than previously thought. This is an of speculation. Nevertheless, it is a matter of some impor important result because the very low fracture energies tance in understanding the design and analysis of coating previously thought necessary will likely be difficult to systems. In one case, the interfacial fracture will be deter- obtain with oxides or other alternative materials mined by the radial tensile strength, while in the other case. The value of 28 J/m" obtained for the fracture energy of it will be determined by the interfacial shear strengths pyrocarbon is in good agreement with literature mode I Understanding the process is also important in interpreting values [12, 13]. Nevertheless, it is a good deal higher than test data. Fiber push/pullout tests, for example, may the 0-3 J/m typically inferred from composites demon- measure a somewhat different property than the one that strating tough behavior, and often thought of as a necessary determines debonding during composite failure condition [5]. This also raises a question regarding the suit The difference in fracture behavior observed in the two ability of the usual use of crack deflection criteria suggested composites discussed in the first section seems to provide by Cook and Gordon[ 14] and the more rigorous analyses of convincing evidence for debonding by the tensile mode in at He and coworkers [15, 16 least one system. The differences in behavior of the treated- fiber composite system as compared to a more convention 3. The nature of crack deflection and suitable criteria untreated-fiber composite, have been attributed to the differ ent interfacial cracking behavior [6,7]. Specifically, the 3.1. Deflection in the coating interfacial crack in untreated-fiber composites has been reported to be confined to the C/SiO2 interface near the l Go Porous consideration of the details of crack deflection fiber surface, or the C layers very near to the interface [7, mplex. The implied hope has been that the problems 201. Such composites are measured to have interfacial frac can be adequately addressed with simplified treatments. As implied by the preceding section, this has sometimes led to has been inferred to strengthen the interface region to a level which is above the strength of the pyrocarbon coating itself, misleading application of crack deflection criteria. For thereby shifting the fracture to the pyrocarbon: the next- example, the He and Hutchinson [15] criterion was derived for deflection in a true interface between two materials and the relevant figure of merit for the competition between The C coatings in both composites are taken to be the crack deflection at the interface and crack propagation Same except perhaps very near the coating/fiber interface. In into the second material was the ratio of interfacial the case of an untreated-fiber composite failing in tension (presumed to be principally mode If) fracture energy to the weak coating/fiber interface region fails, while the coat- issue is crack deflection within a coating, the analogous before the crack enters the coating, due to the stress field in figure of merit will be the ratio of the coating (presumed front of the crack. Had the crack run through the coating, it principally mode ID) fracture energy for a debonding crack would have deflected in the coating. The proof of this state- to coating axial mode I fracture energy [11]. In principle, the ment is provided by the treated-fiber materials, in which the suitability of a material that is intended to promote crack cracks deflect in the coating before reaching the fiber/coat- interface. Provided that the debonding in the weak-inter deflection by cleaving can be evaluated independently of the face(untreated fiber)composites is truly at or very near the a debonding crack within a coating can be expected to devi- coating/fiber interface, this seems to provide a definitive ate towards the coating/fiber interface and, in many cases, to arrive there [1l(see section below). The question nterface composite addressed by He and Hutchinson is then raised, but at a different point in the failure process 3.3. Of-axis shear cracking 3. 2. Tensile crack Recent theoretical and experimental work by Pagano and coworkers [18, 22] has presented strong evidence of a differ- Crack deflection is usually assumed to be literally that; ent mode of crack deflection. The experimental work was the matrix crack tip propagates into the interfacial region performed on highly uniform composites comprising SiC then turns parallel to the fiber surface. However, it has been monofilaments coated first with C, then with TiB2, in glass suggested that the interfacial crack that develops in a matrices. Post-failure analysis revealed that the debonding composite under tension may initiate as a mode I crack in occurred predominately by propagation of a crack in the C the tensile(normal to the fiber surface)stress field ahead of very near the C/Sic interface. However, triangular-section the crack tip [17, 18, and observations on model laminate rings, mountains of C remained on the fiber at the location materials have confirmed the existence of such a failure of matrix cracks, implying double deflection of impinging
assumed and still perform the necessary function of crack deflection. This result suggests that the window of properties that can be possessed by an oxide alternative coating, for example, is larger than previously thought. This is an important result because the very low fracture energies previously thought necessary will likely be difficult to obtain with oxides or other alternative materials. The value of 28 J/m2 obtained for the fracture energy of pyrocarbon is in good agreement with literature mode I values [12,13]. Nevertheless, it is a good deal higher than the 0–3 J/m2 typically inferred from composites demonstrating tough behavior, and often thought of as a necessary condition [5]. This also raises a question regarding the suitability of the usual use of crack deflection criteria suggested by Cook and Gordon [14] and the more rigorous analyses of He and coworkers [15,16]. 3. The nature of crack deflection and suitable criteria 3.1. Deflection in the coating Rigorous consideration of the details of crack deflection is complex. The implied hope has been that the problems can be adequately addressed with simplified treatments. As implied by the preceding section, this has sometimes led to misleading application of crack deflection criteria. For example, the He and Hutchinson [15] criterion was derived for deflection in a true interface between two materials, and the relevant figure of merit for the competition between crack deflection at the interface and crack propagation into the second material was the ratio of interfacial (presumed to be principally mode II) fracture energy to material 2 (mode I) fracture energy. However, if the relevant issue is crack deflection within a coating, the analogous figure of merit will be the ratio of the coating (presumed principally mode II) fracture energy for a debonding crack, to coating axial mode I fracture energy [11]. In principle, the suitability of a material that is intended to promote crack deflection by cleaving can be evaluated independently of the fiber fracture properties. Nevertheless, it is also argued that a debonding crack within a coating can be expected to deviate towards the coating/fiber interface and, in many cases, to arrive there [11] (see section below). The question addressed by He and Hutchinson is then raised, but at a different point in the failure process. 3.2. Tensile crack Crack deflection is usually assumed to be literally that; the matrix crack tip propagates into the interfacial region then turns parallel to the fiber surface. However, it has been suggested that the interfacial crack that develops in a composite under tension may initiate as a mode I crack in the tensile (normal to the fiber surface) stress field ahead of the crack tip [17,18], and observations on model laminate materials have confirmed the existence of such a failure sequence [19]. Since the microscopic details of fracture are difficult to probe experimentally, the exact sequence of events in real fibrous composites has remained a matter of speculation. Nevertheless, it is a matter of some importance in understanding the design and analysis of coating systems. In one case, the interfacial fracture will be determined by the radial tensile strength, while in the other case, it will be determined by the interfacial shear strengths. Understanding the process is also important in interpreting test data. Fiber push/pullout tests, for example, may measure a somewhat different property than the one that determines debonding during composite failure. The difference in fracture behavior observed in the two composites discussed in the first section seems to provide convincing evidence for debonding by the tensile mode in at least one system. The differences in behavior of the treated- fiber composite system as compared to a more conventional untreated-fiber composite, have been attributed to the different interfacial cracking behavior [6,7]. Specifically, the interfacial crack in untreated-fiber composites has been reported to be confined to the C/SiO2 interface near the fiber surface, or the C layers very near to the interface [7, 20]. Such composites are measured to have interfacial fracture energies of no more than a few J/m2 . The fiber treatment has been inferred to strengthen the interface region to a level which is above the strength of the pyrocarbon coating itself, thereby shifting the fracture to the pyrocarbon: the nextweakest link [7,21]. The C coatings in both composites are taken to be the same except perhaps very near the coating/fiber interface. In the case of an untreated-fiber composite failing in tension, the weak coating/fiber interface region fails, while the coating itself does not. This implies that the interface must fail before the crack enters the coating, due to the stress field in front of the crack. Had the crack run through the coating, it would have deflected in the coating. The proof of this statement is provided by the treated-fiber materials, in which the cracks deflect in the coating before reaching the fiber/coating interface. Provided that the debonding in the weak-interface (untreated fiber) composites is truly at or very near the coating/fiber interface, this seems to provide a definitive sequence of events for the deflection process in weakinterface composites. 3.3. Off-axis shear cracking Recent theoretical and experimental work by Pagano and coworkers [18,22] has presented strong evidence of a different mode of crack deflection. The experimental work was performed on highly uniform composites comprising SiC monofilaments coated first with C, then with TiB2, in glass matrices. Post-failure analysis revealed that the debonding occurred predominately by propagation of a crack in the C very near the C/SiC interface. However, triangular-section rings, ‘mountains’ of C remained on the fiber at the location of matrix cracks, implying double deflection of impinging 522 R.J. Kerans, T.A. Parthasarathy / Composites: Part A 30 (1999) 521–524
R.J. Kerans, T.A. Parthasarathy /Composites: Part A 30(1999)521-52 matrix cracks in the C layer, followed by propagation of short-period crack regime would correspond to initial crack each crack obliquely to the fiber surface, followed by deflec- deflection in the coating an od crack would tion along(or near) the surface. The radial stresses in the correspond to the coating/fiber interfacial crack oatings were calculated using the Axisymmetric Damage Model to be compressive, which would tend to inhibit axial shear or radial tension modes. The maximum stresses in the 4 Interfacial roughness field of an impinging matrix crack that could lead to crack ing were found to be shear stresses along planes consistent The potential of significant effects due to surface rough- with the oblique paths forming the mountainous' ring less was first discussed in the context of increased radial Evidence was also found that fiber failure occurs predomi- stresses due to the geometric misfit [24]. Contradictions in nately in the stress concentration at the tip of the debonding measured and calculated sliding friction led to the sugges- tion of roughness effects, and experimental confirmation of them by the push back seating drop'of Jero and coworkers 34. crack within a coating [25, 26]. A simple geometric misfit model has provided further evidence that the effects can be important [27] Further consideration of the failure process for a crack Briefly, a fiber pulling out of a matrix under axial loading running within a coating implies additional complexity is subjected to radial stresses which differ along its length regarding both deflection criteria and roughness, and The interfacial normal stress in the un-slipped region provides interesting speculation on the degree to which (Region I)ahead of the crack tip is determined by the resi- oxide coatings can be expected to provide protection against dual stresses, and to a minor degree, by differences in Pois- oxidation of the fiber [11]. Consider the tensile failure sons ratios and the applied axial stress. Well behind the process of a composite in which cracks deflect in the coat- crack tip(Region If), the displacement between fiber and ing. A matrix crack impinges on a coated fiber and is matrix is sufficient to effect the full geometric misfit, and the deflected in the coating. The consequent debonding crack normal stress is the sum of the residual stresses and the propagates some distance in the coating away from the stresses resulting from the full effect of the misfit. The matrix crack plane. With subsequent loading, the matrix roughness induced stresses may be larger than the thermal crack bypasses the fiber and the debonding crack propagates stresses. The intermediate region(Region If) extends with somewhat further, within the coating. At that point, the increasing misfit from the crack tip to the beginning of crack is bridged by a fiber still coated by the remaining Region Ill. This region both complicates analysis and intact portion of the coating. It is this remaining coating gives rise to a number of interesting effects. A full solution which could provide some protection. However, unless the of the problem for one simple form of roughness [27] has coating is extremely strain tolerant, it must fail in tension shown that the friction can actually be highest in Region Il with subsequent loading, introducing another mode I crack. and that the effects can be very much larger than the region That crack may deflect into another mode ll crack running Ill misfit alone. Fiber pushout load-deflection curves fo parallel to the fiber axis, but the process must repeat until the composites where the Region Il effects are large, such as coating is completely cracked and there is a debonding those of the first section, demonstrate unusual features such crack running in the fiber/coating interface. The only possi- as upward curvature and discontinuous derivatives. Comp bility for retaining the coating is if it is as strain tolerant (to site behavior may not be well described by conventional axial tensile strains) as the fiber (in the neighborhood of models 1%), i.e. far more strain tolerant than would be expected from equivalent bulk materials. Although thin coatings can be expected to exhibit increasing strain-to-failure with 5 Summary decreasing thickness(see, for example, [23]), such high alues may be problematical for approaches such as porous The coatings that have enabled the development of oxides. This scenario implies two consequences: (1)even conventional composites have fortuitously possessed a though crack deflection occurred in the coating, post failure suite of properties well suited to the task. New oxide coat analysis may show cracks in the coating/fiber interface, and ings will require active design of the coatings, and of the (2)any oxidation protection provided by the coating may be entire composite system, to accomplish the same mechani- limited by the tensile strain-to-failure of the coating. The cal goals. This, in turn, will require a more thorough under- first of these requires that the conclusions based on the standing of crack deflection and sliding processes than arguments of the preceding section be based on sound heretofore necessary. The entire process, from conception, evidence regarding the location of the initial crack deflec- through design, processing, and evaluation, to ultimate tion because all debonding cracks will tend to eventually run performance of composites with new oxidation-resistant in or near the interface. This scenario is also consistent with interface control systems will be greatly facilitated by, if the analysis based on two successive modes of cracking not dependent upon, understanding the details that govern behavior used in the preceding section, wherein the initial crack deflection, debonding and sliding
matrix cracks in the C layer, followed by propagation of each crack obliquely to the fiber surface, followed by deflection along (or near) the surface. The radial stresses in the coatings were calculated using the Axisymmetric Damage Model to be compressive, which would tend to inhibit axial shear or radial tension modes. The maximum stresses in the field of an impinging matrix crack that could lead to cracking were found to be shear stresses along planes consistent with the oblique paths forming the ‘mountainous’ rings. Evidence was also found that fiber failure occurs predominately in the stress concentration at the tip of the debonding crack. 3.4. Crack path within a coating Further consideration of the failure process for a crack running within a coating implies additional complexity regarding both deflection criteria and roughness, and provides interesting speculation on the degree to which oxide coatings can be expected to provide protection against oxidation of the fiber [11]. Consider the tensile failure process of a composite in which cracks deflect in the coating. A matrix crack impinges on a coated fiber and is deflected in the coating. The consequent debonding crack propagates some distance in the coating away from the matrix crack plane. With subsequent loading, the matrix crack bypasses the fiber and the debonding crack propagates somewhat further, within the coating. At that point, the crack is bridged by a fiber still coated by the remaining intact portion of the coating. It is this remaining coating which could provide some protection. However, unless the coating is extremely strain tolerant, it must fail in tension with subsequent loading, introducing another mode I crack. That crack may deflect into another mode II crack running parallel to the fiber axis, but the process must repeat until the coating is completely cracked and there is a debonding crack running in the fiber/coating interface. The only possibility for retaining the coating is if it is as strain tolerant (to axial tensile strains) as the fiber (in the neighborhood of 1%), i.e. far more strain tolerant than would be expected from equivalent bulk materials. Although thin coatings can be expected to exhibit increasing strain-to-failure with decreasing thickness (see, for example, [23]), such high values may be problematical for approaches such as porous oxides. This scenario implies two consequences: (1) even though crack deflection occurred in the coating, post failure analysis may show cracks in the coating/fiber interface, and (2) any oxidation protection provided by the coating may be limited by the tensile strain-to-failure of the coating. The first of these requires that the conclusions based on the arguments of the preceding section be based on sound evidence regarding the location of the initial crack deflection because all debonding cracks will tend to eventually run in or near the interface. This scenario is also consistent with the analysis based on two successive modes of cracking behavior used in the preceding section, wherein the initial short-period crack regime would correspond to initial crack deflection in the coating and the long-period crack would correspond to the coating/fiber interfacial crack. 4. Interfacial roughness The potential of significant effects due to surface roughness was first discussed in the context of increased radial stresses due to the geometric misfit [24]. Contradictions in measured and calculated sliding friction led to the suggestion of roughness effects, and experimental confirmation of them by the ‘push back seating drop’ of Jero and coworkers [25,26]. A simple geometric misfit model has provided further evidence that the effects can be important [27]. Briefly, a fiber pulling out of a matrix under axial loading is subjected to radial stresses which differ along its length. The interfacial normal stress in the un-slipped region (Region I) ahead of the crack tip is determined by the residual stresses, and to a minor degree, by differences in Poisson’s ratios and the applied axial stress. Well behind the crack tip (Region III), the displacement between fiber and matrix is sufficient to effect the full geometric misfit, and the normal stress is the sum of the residual stresses and the stresses resulting from the full effect of the misfit. The roughness induced stresses may be larger than the thermal stresses. The intermediate region (Region II) extends with increasing misfit from the crack tip to the beginning of Region III. This region both complicates analysis and gives rise to a number of interesting effects. A full solution of the problem for one simple form of roughness [27] has shown that the friction can actually be highest in Region II and that the effects can be very much larger than the Region III misfit alone. Fiber pushout load–deflection curves for composites where the Region II effects are large, such as those of the first section, demonstrate unusual features such as upward curvature and discontinuous derivatives. Composite behavior may not be well described by conventional models. 5. Summary The coatings that have enabled the development of conventional composites have fortuitously possessed a suite of properties well suited to the task. New oxide coatings will require active design of the coatings, and of the entire composite system, to accomplish the same mechanical goals. This, in turn, will require a more thorough understanding of crack deflection and sliding processes than heretofore necessary. The entire process, from conception, through design, processing, and evaluation, to ultimate performance of composites with new oxidation-resistant interface control systems will be greatly facilitated by, if not dependent upon, understanding the details that govern crack deflection, debonding and sliding. R.J. Kerans, T.A. Parthasarathy / Composites: Part A 30 (1999) 521–524 523
R.J. Kerans, T.A. Parthasarathy /Composites. Part 4 30(1999)521-524 References biomedical applications. Mat Res Soc Symp Proc, Mat Res Soc 995383229-254 [1 Prewo K, Brennan JJ. High-strength silicon carb [14] Cook J, Gordon JE. A mechanism for the control of crack propagation matrix composites. J Mat Sci 1980; 15(2): 46 in all-brittle systems. Proc R Soc Lond 1964: A282: 508-520 [2] Evans AG, Zok FW. Review: the physics and of fibre. [15] He MY, Hutchinson Jw. Crack deflection at an interface between inforced brittle matrix composites. J Mat 29:3857 dissimilar elastic materials. Int J Solids Structures 1989; 25(9) 1053-1087 3] Kerans R, Hay Rs, Pagano NJ, Parthasarathy TA. The role of [16 He MY, Evans AG, Hutchinson Jw. Crack deflection at an interface between dissimilar elastic materials: role of residual stresses. Int J 1989,68(2)429-442 Solids Structures 1994: 31(24): 3443-3455 [4]Kerans R. Issues in the control of fiber/matrix interfaces in ceramic [17] Pagano NJ, Brown Ill HW. The full cell cracking mode in unidirec- composites. Scripta Metall Mat 1994, 31(8): 1079-1085 nal brittle matrix composites. Composites 1993: 24(2): 69-83 [5] Cao HC, Bischoff E, Sbaizero O, Ruhle M, Evans AG, Marshall DB [18 Pagano NJ. On the micromechanical failure modes in a class of ideal Brennan JJ. Effect of interfaces on the properties of fiber-reinforced brittle matrix composites part 1: coated fiber composites. Composites ramics. J Am Ceram Soc 1990; 73(6): 1691-1699 Part B19982913:93-119 [6]Droillard C, Lamon J. Fracture toughness of 2D woven SiC/SiC [19]Lee W, Howard SJ, Clegg WJ. Growth of interface defects and its mposites with multilayered interphases. J Am Ceram Soc effect on crack deflection and toughening criteria. Acta Mater 1996;79(4):849-85 996;44(10:3905-3922. [7 Droillard C, Lamon J, Bourrat X Strong interfaces in CMCs, condi- [20 Droillard C. Ph. D. thesis, University of bordeaux tion for efficient multilayered interphases. Mat Res Soc Symp Proc (21 Rebillat F, Lamon J, Naslain R, Lara-Curzio E, Fe Mat Res soc1995;365:371-376 TM. Interfacial bond strength in nicalon/C/SiC [8)Naslain R. Fiber-matrix interphases and interfaces in ceramic matrix died by single-fiber push-out tests. J Am Ceram Soc omposites processed by CVI Composite Interfaces 1993 1(3): 253 1(4):965-978 [22 Pagano NJ, Dutton RE, Kim RY, Ultimate tension failure of borosl- [9 Lamon J. Interfaces and interfacial mechanics: influence on the ate glass-SiC fiber unidirectional composites. J Am Ceram Soc, in mechanical behavior of ceramic matrix composites. Journal de Physi- que IV, Coloque C7, supplement to Journal de Physique Ill [23] Hu Ms, Thouless MD, Evans AG. The decohesion of thin films from 1993:3:1607-1616 brittle substrates. Acta Metall 1988: 36(5): 1301-1307 10] Lissart N, Lamon J. Damage and failure in ceramic matrix minicom- [24] Kerans RI, Parthasarathy TA. Theoretical analysis of the fiber pullout posites: experimental study and model. Acta Mater 1997; 45(3): 1025- and pushout tests. J Am Ceram Soc 1991: 74(7): 1585-1596 [25]Jero PD, Kerans R. The contribution of interfacial roughness to 11] Kerans R, Parthasarathy TA, Rebillat F, Lamon J. Interface proper- sliding friction of ceramic fibers in a glass matrix. Scripta Metall es in high strength NICALon"/C/SiC composites as determined by Mater1991;24:2315-231 ough surface analysis of fiber pushout tests. J Am Ceram Soc 1998 [26 Jero PD, Kerans R, Parthasarathy TA. Effect of interfacial roughness l(7):1881-1887 on the frictional stress measured using pushout tests. J Am Ceramic 12 Sakai M, Bradt RC, Fischbach DB Fracture toughness anisotropy of a Soc1991;74(11)2793-2801 pyrolytic carbon. J Mat Sci 1986, 21: 1491-1501 27] Parthasarathy TA, Marshall DB, Kerans RJ. Analysis of the effect of 3] Ritchie RO, Dauskardt RH, Gerberich ww, Strojny A, Lilleodden E interfacial roughness on fiber debonding and sliding in brittle matrix Fracture, fatigue and indentation behavior of pyrolytic carbon for composites. Acta Metall Mater 1994; 42(11): 3773-3784
References [1] Prewo K, Brennan JJ. High-strength silicon carbide fiber-reinforced glass matrix composites. J Mat Sci 1980;15(2):463–468. [2] Evans AG, Zok FW. Review: the physics and mechanics of fibrereinforced brittle matrix composites. J Mat Sci 1994;29:3857– 3896. [3] Kerans RJ, Hay RS, Pagano NJ, Parthasarathy TA. The role of the fiber-matrix interface in ceramic composites. Ceramic Bull 1989;68(2):429–442. [4] Kerans RJ. Issues in the control of fiber/matrix interfaces in ceramic composites. Scripta Metall Mat 1994;31(8):1079–1085. [5] Cao HC, Bischoff E, Sbaizero O, Ruhle M, Evans AG, Marshall DB, Brennan JJ. Effect of interfaces on the properties of fiber-reinforced ceramics. J Am Ceram Soc 1990;73(6):1691–1699. [6] Droillard C, Lamon J. Fracture toughness of 2D woven SiC/SiC composites with multilayered interphases. J Am Ceram Soc 1996;79(4):849–858. [7] Droillard C, Lamon J, Bourrat X. Strong interfaces in CMCs, condition for efficient multilayered interphases. Mat Res Soc Symp Proc, Mat Res Soc 1995;365:371–376. [8] Naslain R. Fiber-matrix interphases and interfaces in ceramic matrix composites processed by CVI. Composite Interfaces 1993;1(3):253– 286. [9] Lamon J. Interfaces and interfacial mechanics: influence on the mechanical behavior of ceramic matrix composites. Journal de Physique IV, Coloque C7, supplement to Journal de Physique III 1993;3:1607–1616. [10] Lissart N, Lamon J. Damage and failure in ceramic matrix minicomposites: experimental study and model. Acta Mater 1997;45(3):1025– 1044. [11] Kerans RJ, Parthasarathy TA, Rebillat F, Lamon J. Interface properties in high strength NICALONe/C/SiC composites as determined by rough surface analysis of fiber pushout tests. J Am Ceram Soc 1998; 81(7):1881–1887. [12] Sakai M, Bradt RC, Fischbach DB. Fracture toughness anisotropy of a pyrolytic carbon. J Mat Sci 1986;21:1491–1501. [13] Ritchie RO, Dauskardt RH, Gerberich WW, Strojny A, Lilleodden E. Fracture, fatigue and indentation behavior of pyrolytic carbon for biomedical applications. Mat Res Soc Symp Proc, Mat Res Soc 1995;383:229–254. [14] Cook J, Gordon JE. A mechanism for the control of crack propagation in all-brittle systems. Proc R Soc Lond 1964;A282:508–520. [15] He MY, Hutchinson JW. Crack deflection at an interface between dissimilar elastic materials. Int J Solids Structures 1989;25(9): 1053–1087. [16] He MY, Evans AG, Hutchinson JW. Crack deflection at an interface between dissimilar elastic materials: role of residual stresses. Int J Solids Structures 1994;31(24):3443–3455. [17] Pagano NJ, Brown III HW. The full cell cracking mode in unidirectional brittle matrix composites. Composites 1993;24(2):69–83. [18] Pagano NJ. On the micromechanical failure modes in a class of ideal brittle matrix composites part I: coated fiber composites. Composites Part B 1998;2913:93–119. [19] Lee W, Howard SJ, Clegg WJ. Growth of interface defects and its effect on crack deflection and toughening criteria. Acta Mater 1996;44(10):3905–3922. [20] Droillard C. Ph.D. thesis, University of Bordeaux, France, 1993. [21] Rebillat F, Lamon J, Naslain R, Lara-Curzio E, Ferber MK, Besmann TM, Interfacial bond strength in nicalon/C/SiC composite materials as studied by single-fiber push-out tests. J Am Ceram Soc 1998;81(4):965–978. [22] Pagano NJ, Dutton RE, Kim RY, Ultimate tension failure of borosilicate glass-SiC fiber unidirectional composites. J Am Ceram Soc, in review. [23] Hu MS, Thouless MD, Evans AG. The decohesion of thin films from brittle substrates. Acta Metall 1988;36(5):1301–1307. [24] Kerans RJ, Parthasarathy TA. Theoretical analysis of the fiber pullout and pushout tests. J Am Ceram Soc 1991;74(7):1585–1596. [25] Jero PD, Kerans RJ. The contribution of interfacial roughness to sliding friction of ceramic fibers in a glass matrix. Scripta Metall Mater 1991;24:2315–2318. [26] Jero PD, Kerans RJ, Parthasarathy TA. Effect of interfacial roughness on the frictional stress measured using pushout tests. J Am Ceramic Soc 1991;74(11):2793–2801. [27] Parthasarathy TA, Marshall DB, Kerans RJ. Analysis of the effect of interfacial roughness on fiber debonding and sliding in brittle matrix composites. Acta Metall Mater 1994;42(11):3773–3784. 524 R.J. Kerans, T.A. Parthasarathy / Composites: Part A 30 (1999) 521–524