Anti symmetric four point bending specimens with different thickness, without and with guiding grooves, were used to conduct Mode Ⅱ fracture test and study the effect of specimen thickness on Mode Ⅱ fracture toughne...Anti symmetric four point bending specimens with different thickness, without and with guiding grooves, were used to conduct Mode Ⅱ fracture test and study the effect of specimen thickness on Mode Ⅱ fracture toughness of rock. Numerical calculations show that the occurrence of Mode Ⅱ fracture in the specimens without guiding grooves (when the inner and outer loading points are moved close to the notch plane) and with guiding grooves is attributed to a favorable stress condition created for Mode Ⅱ fracture, i.e. tensile stress at the notch tip is depressed to be lower than the tensile strength or to be compressive stress, and the ratio of shear stress to tensile stress at notch tip is very high. The measured value of Mode Ⅱ fracture toughness K ⅡC decreases with the increase of the specimen thickness or the net thickness of specimen. This is because a thick specimen promotes a plane strain state and thus results in a relatively small fracture toughness.展开更多
The etching technique of the single-lined zero-thickness specimen grating is applied to the surface of the SiC fiber toughening Si3N4 ceramic composite specimen. The position of the crack and the crack length during t...The etching technique of the single-lined zero-thickness specimen grating is applied to the surface of the SiC fiber toughening Si3N4 ceramic composite specimen. The position of the crack and the crack length during the process of crack extension when the load is applied and gradually increased can be determined by recording the output voltage value of the Wheatstone bridge in which the ceramic specimen with the fracture grating on is located. The crack-growth-resistance(R-curve) of this material is thus obtained.展开更多
The present study attempts to investigate the effect of moisture conditioning on the in- direct tensile strength （ITS） of cold recycled mixture with bitumen emulsion. Firstly, samples were prepared using a Superpave...The present study attempts to investigate the effect of moisture conditioning on the in- direct tensile strength （ITS） of cold recycled mixture with bitumen emulsion. Firstly, samples were prepared using a Superpave gyratory compactor. They were hence condi- tioned using moisture induced sensitivity tester （MIST） device. Factorial design was carried out considering four factors each at two different levels. These factors were specimen thickness, air voids content, pressure and number of cycles. In the MIST device, samples are cyclically subjected to water pressure through the sample pores. The MIST conditioned samples were tested for indirect tensile strength. The analysis of two-level full-factorial designed experiments revealed that all four factors have a negative effect on tensile strength of cold recycled mixture with bitumen emulsion. Specimen thickness was the most significant factor affecting the tensile strength followed by air voids content. In two- factor interaction, specimen thickness-number of cycles, air voids content-pressure, and pressure-number of cycles were significant. The most significant three-factor interaction was specimen thickness-pressure-number of cycles. The results from the study suggest that in measuring tensile strength, the appropriate specimen thickness and air voids content should be selected to quantify the representative tensile strength for in-situ conditions.展开更多
基金TheNationalNaturalScienceFoundationofChina (No :496 72 16 4)
文摘Anti symmetric four point bending specimens with different thickness, without and with guiding grooves, were used to conduct Mode Ⅱ fracture test and study the effect of specimen thickness on Mode Ⅱ fracture toughness of rock. Numerical calculations show that the occurrence of Mode Ⅱ fracture in the specimens without guiding grooves (when the inner and outer loading points are moved close to the notch plane) and with guiding grooves is attributed to a favorable stress condition created for Mode Ⅱ fracture, i.e. tensile stress at the notch tip is depressed to be lower than the tensile strength or to be compressive stress, and the ratio of shear stress to tensile stress at notch tip is very high. The measured value of Mode Ⅱ fracture toughness K ⅡC decreases with the increase of the specimen thickness or the net thickness of specimen. This is because a thick specimen promotes a plane strain state and thus results in a relatively small fracture toughness.
文摘The etching technique of the single-lined zero-thickness specimen grating is applied to the surface of the SiC fiber toughening Si3N4 ceramic composite specimen. The position of the crack and the crack length during the process of crack extension when the load is applied and gradually increased can be determined by recording the output voltage value of the Wheatstone bridge in which the ceramic specimen with the fracture grating on is located. The crack-growth-resistance(R-curve) of this material is thus obtained.
基金supported by the National Natural Science Foundation of China(grant No.51308477)
文摘The present study attempts to investigate the effect of moisture conditioning on the in- direct tensile strength （ITS） of cold recycled mixture with bitumen emulsion. Firstly, samples were prepared using a Superpave gyratory compactor. They were hence condi- tioned using moisture induced sensitivity tester （MIST） device. Factorial design was carried out considering four factors each at two different levels. These factors were specimen thickness, air voids content, pressure and number of cycles. In the MIST device, samples are cyclically subjected to water pressure through the sample pores. The MIST conditioned samples were tested for indirect tensile strength. The analysis of two-level full-factorial designed experiments revealed that all four factors have a negative effect on tensile strength of cold recycled mixture with bitumen emulsion. Specimen thickness was the most significant factor affecting the tensile strength followed by air voids content. In two- factor interaction, specimen thickness-number of cycles, air voids content-pressure, and pressure-number of cycles were significant. The most significant three-factor interaction was specimen thickness-pressure-number of cycles. The results from the study suggest that in measuring tensile strength, the appropriate specimen thickness and air voids content should be selected to quantify the representative tensile strength for in-situ conditions.
