Hole Diameter Effect on Open-hole Tensile Mechanical Property of MI-SiCf/SiC Composites

doi:10.15541/jim20250347

Abstract

Abstract:

To meet the design requirements for perforated structures in aero-engine hot-section components made of MI-SiC_f/SiC composites, this study prepared unnotched specimens and five types of open-hole specimens with different diameters (D=1-9 mm), and conducted room-temperature tensile tests. By integrating digital image correlation and acoustic emission techniques, the full-field strain evolution and internal damage signals were monitored in real time, systematically elucidating the influence of hole diameter on damage initiation threshold and evolution behavior. A three-dimensional finite element model was established to analyze the competing mechanisms between material nonlinearity, stress concentration at the hole-edge, and stress interaction at the hole-edge. The results indicate that the open-hole tensile strength exhibits a nonlinear relationship with the hole diameter: when D≤3 mm, the strength increases slowly with increasing diameter, whereas it decreases sharply for D>3 mm. A critical threshold exists concerning the width-to-diameter ratio (W/D): specifically, when W/D<3, stress concentration interference between the hole and the specimen edge leads to a pronounced decline in load-bearing capacity, with geometric effects dominating the failure behavior. Moreover, damage initiation stress decreases with increasing hole diameter. Small-hole specimens (D≤3 mm) maintain a sequential damage evolution process, while large-hole specimens (D>3 mm) exhibit concurrent multiple damage modes. Finite element analysis reveals that the stress peak shifts away from the hole edge once the material enters the nonlinear stage, resulting in early failure in specimens with diameter of 1-2 mm due to the overlap between the high-stress zone and inherent material defects. Larger holes require a larger stress redistribution zone. When W/D exceeds the critical value of 3, the available material width becomes insufficient, ultimately leading to a sharp decrease in nominal tensile strength. In conclusion, the optimal open-hole tensile performance of MI-SiC_f/SiC composites is achieved at a hole diameter of 3 mm. Reinforcement designs are recommended for open-hole structures with W/D<3.

Key words: MI-SiC_f/SiC composite, open-hole tensile, hole diameter effect, digital image correlation, acoustic emission

CLC Number:

V231
TB332

WANG Yana, SONG Jiupeng, WANG Hairun, LI Tianshan, JIAO Jian. Hole Diameter Effect on Open-hole Tensile Mechanical Property of MI-SiC_f/SiC Composites[J]. Journal of Inorganic Materials, 2026, 41(5): 653-662.

Figures/Tables 19

Fig. 1 Test specimen configuration, dimensions and photograph of the loading setup (a) Open-hole tensile specimen; (b) Unnotched tensile specimen; (c) Photograph of the specimen under loading. Unit: mm

Fig. 2 Schematic diagram of stress distribution characteristics around the hole in an open-hole tensile specimen

Table 1 Specimen geometry and theoretical stress concentration factor

Specimen	D/mm	W/D	K_t
K0	0	/	/
K1	1	18	2.844
K2	2	9	2.707
K3	3	6	2.582
K4	6	3	2.302
K5	9	2	2.130

Fig. 3 Comparison of tensile curves and fracture surface morphologies between unnotched and open-hole specimens (a) Nominal open-hole tensile stress-strain curves; (b) Net-section stress-strain curves; (c) Fracture morphologies of OHT specimens

Table 2 Tensile stiffness and strength for specimens with different hole diameters

Specimen	D/ mm	E_OHT/ GPa	E_NS/ GPa	S_OHT/ MPa	S_NS/ MPa	σ_{p_OHT}/ MPa	σ_{p_NS}/ MPa	σ_peak/ MPa
K0	0	206	206	228	228	125	125	125
K1	1	200	212	155	164	106	112	301
K2	2	203	229	158	177	98.8	111	267
K3	3	204	245	162	194	98.1	117	253
K4	6	186	278	120	179	90.0	134	207
K5	9	83.2	164	47.3	93.1	20.5	40.5	43.7

Fig. 4 Effect of hole diameter on (a) tensile strength properties and (b) module properties of specimens

Fig. 5 (a) Peak frequency and (b) normalized cumulative energy curves of unnotched specimen

Fig. 6 (a) Finite element model of the open-hole specimen and (b) corresponding applied loads and boundary conditions

Fig. 7 Stress predictions around holes in K1-K5 specimens (a) Elastic model results; (b) Nonlinear model results; (c) Stress distribution along hole edge to the specimen edge line

Table 3 Characteristic dimension analysis for specimens with different hole diameters

Specimen	D/mm	L_e/mm	L_p/mm
K1	1	0.159	0.225
K2	2	0.337	0.505
K3	3	0.559	0.781
K4	6	0.584	/
K5	9	/	/

Fig. S1 CT reconstructed images of internal defects in specimens with different hole diameters (a) K1 specimen; (b) K2 specimen; (c) K3 specimen; (d) K4 specimen; (e) K5 specimen

Fig. S2 (a) Peak frequency and (b) normalized cumulative energy curves of K1 OHT specimen

Fig. S3 (a) Peak frequency and (b) normalized cumulative energy curves of K2 OHT specimen

Fig. S4 (a) Peak frequency and (b) normalized cumulative energy curves of K3 specimen

Fig. S5 (a) Peak frequency and (b) normalized cumulative energy curves of K4 specimen

Fig. S6 (a) Peak frequency and (b) normalized cumulative energy curves of K5 specimen

Fig. S7 Longitudinal tensile strain distribution along the hole-to-side line (a) K1 specimen; (b) K2 specimen; (c) K3 specimen; (d) K4 specimen; (e) K5 specimen

Table S1 Variation of the full-field surface strain at different stress levels for specimens with five different hole diameters

	σ_OHT/MPa	46	82	113	138	149	155
K1
K2	σ_OHT/MPa	23.5	84.0	112	144	155	158
K2
K3	σ_OHT/MPa	34.1	78.0	108	142	155	162
K3
K4	σ_OHT/MPa	29.1	43.0	85.2	107	120	103
K4
K5	σ_OHT/MPa	15.1	28.0	36.1	47.2	46.0	37.1
K5

Table S2 DIC strain contour map of the stress corresponding to acoustic emission signal feature points

Specimen	First occurrence of acoustic emission signals on the peak frequency curve	First occurrence of an energy jump on the normalized cumulative energy curve	Peak frequency reaches the first peak point
K1	σ_OHT=32.2 MPa	σ_OHT=52.7 MPa	σ_OHT=102 MPa
K2	σ_OHT=23.1 MPa	σ_OHT=37.4 MPa	σ_OHT=121 MPa
K3	σ_OHT=27.0 MPa	σ_OHT=36.6 MPa	σ_OHT=104 MPa
K4	σ_OHT=16.9 MPa	σ_OHT=29.5 MPa	σ_OHT=44.1 MPa
K5	σ_OHT=14.4 MPa	σ_OHT=16.2 MPa	σ_OHT=47.4 MPa

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