N Takeda, M. Kiriyama/Composites: Part A 30(1999)593-597 Matrix C地 Ply Matrix Crack Matrix Crack ll 90"Ply (a)[0390103],E=0.25% (a)"Sky 200x 100pm 今:计 Matrix Crack (a)[03902/03],E=0.20% Fig. 1. Photographs of replicas showing cracks under tensile load (b) using polyacetate films. Matrix crack evolution in both 0 and 90 plies was quantitatively measured by observing Fig. 2. In situ SEM photographs of fiber/matrix sliding on specimen surfaces with printed micro-lines. replicas through an optical microscope after the tests The in situ SEM/micro-line technique has been estab- lished recently to quantitatively measure the microscopic pattems in CMC cross-ply laminates are matrix cracks forced composites under loading [ll], and is used here for generating in both 0 and 90 plies. Matrix cracks penetrat ing into both 0 and 90 plies are dominant in [0, 901/031 brittle matrix composites. Parallel micro-lines were printed laminates. However, matrix cracks only existing in 0 plies on the parallel-sided specimen surfaces by a photo-lithogra shy technique. Micro-line patterns of l um in width and 3 can also be observed more often from the earlier loading or 5 um in gap were used on specimens in the same sizes as stage as the number of 90 plies increases. The following those used in the replica observation. The printed specimens experimental formula can be obtained by fitting all experi- mental data were loaded at the same cross-head speed inside a SEM with a servo-hydraulic loading stage as well as a temperate control unit. Two-dimensional distribution of fiber/matrix =p2.390m+189 interfacial debonding and sliding in 0 plies, in particular where the matrix crack densities or the numbers of cracks was observed and measured quantitatively as a function of per unit length in the tensile direction in 0 and 90 plies are the stress level. Photographs were taken at various loading denoted by PI and p2, respectively ages and fed into a computer as digital images, and then the relative displacement was digitally measured. The reso- lution in the displacement is 0.02 um in the present study. 3.2. In situ observation of interfacial debonding and sliding Fig. 2 shows in situ SEM photographs of a damage state 3. Experimental results near a 0 matrix crack among matrix cracks penetrating into both 0 and 90 plies. x and Ar are defined as the distance 3. 1. Initiation and growth of matrix cracks from a crack in the direction of the given tensile stress and the relative displacement or sliding of a micro-line Fig. 1 presents photographs of replicas, which show respectively. Ld is defined as the debonding length on ausing polyacetate films. Matrix crack evolution in both 08 and 908 plies was quantitatively measured by observing replicas through an optical microscope after the tests. The in situ SEM/micro-line technique has been estab￾lished recently to quantitatively measure the microscopic deformation and interfacial damage evolution in fiber-rein￾forced composites under loading [11], and is used here for brittle matrix composites. Parallel micro-lines were printed on the parallel-sided specimen surfaces by a photo-lithogra￾phy technique. Micro-line patterns of 1 mm in width and 3 or 5 mm in gap were used on specimens in the same sizes as those used in the replica observation. The printed specimens were loaded at the same cross-head speed inside a SEM with a servo-hydraulic loading stage as well as a temperate control unit. Two-dimensional distribution of fiber/matrix interfacial debonding and sliding in 08 plies, in particular, was observed and measured quantitatively as a function of the stress level. Photographs were taken at various loading stages and fed into a computer as digital images, and then the relative displacement was digitally measured. The reso￾lution in the displacement is 0.02 mm in the present study. 3. Experimental results 3.1. Initiation and growth of matrix cracks Fig. 1 presents photographs of replicas, which show matrix cracks under tensile load. Characteristic damage patterns in CMC cross-ply laminates are matrix cracks generating in both 08 and 908 plies. Matrix cracks penetrat￾ing into both 08 and 908 plies are dominant in [03/901/03] laminates. However, matrix cracks only existing in 08 plies can also be observed more often from the earlier loading stage as the number of 908 plies increases. The following experimental formula can be obtained by fitting all experi￾mental data, r1 ˆ r …1:390m11:889† 2 × 1024 …1† where the matrix crack densities or the numbers of cracks per unit length in the tensile direction in 08 and 908 plies are denoted by r 1 and r 2, respectively. 3.2. In situ observation of interfacial debonding and sliding Fig. 2 shows in situ SEM photographs of a damage state near a 08 matrix crack among matrix cracks penetrating into both 08 and 908 plies. x and Dx are defined as the distance from a crack in the direction of the given tensile stress and the relative displacement or sliding of a micro-line, respectively. Ld is defined as the debonding length on a 594 N. Takeda, M. Kiriyama / Composites: Part A 30 (1999) 593–597 Fig. 1. Photographs of replicas showing cracks under tensile load. Fig. 2. In situ SEM photographs of fiber/matrix sliding on specimen surfaces with printed micro-lines