Microcrack Evaluation Research Articles

Fracture Analysis Based on Quantitative Evaluation of Microcracking in Ceramics Using AE Source Characterization

Quantitative detection of microcracks during fracture process of alumina was carried out by AE source characterization, which enables the quantitative characterization of the size, nucleation velocity and fracture mode, as well as nucleation time and location of individual microcracks. Fracture toughness tests of SENB specimens of two types of alumina with different grain size and purity were carried out in air and water. AE signals emitted from microcrackings were detected by piezoelectric transducers. The combined response function of the specimen and measurement system was experimentally determined using a pencil lead breaking as a simulated source. Then AE source function which describes the nature of microcrack nucleation was determined by the inverse calculation using obtained response function and detected signal. Consequently, it was clarified that the size of microcrack in water was larger than that in air for both alumina and larger microcracks nucleated in water resulted in the degradation of fracture resistance.

16 Three-Dimensional Evaluation of Micro-Cracks in Human Trabecular Bone

16 Three-Dimensional Evaluation of Micro-Cracks in Human Trabecular Bone

Nondestructive evaluation of microcracks by laser-induced focused ultrasound

Photoacoustic transformation of laser pulses at a concave stainless steel surface immersed in water delivered short, focused, ultrasonic pressure pulses to the free surface of a sample placed in the focal region. The probe-beam-deflection method was employed to detect the resulting transient surface slope of the surface distortions in the frequency range ⩽100MHz. Absolute calibration of the setup indicates strains of ∼10−3. Clear evidence for characteristic changes in the transient waveforms was observed near single cracks at the surface. Therefore, this novel method is suitable for nondestructive evaluation and characterization of bulk and surface defects.

Nondestructive evaluation of micro-cracks in a ceramic ferrule by resonant ultrasound spectroscopy

We performed a nondestructive evaluation of micro-cracks in ceramic ferrules for optical fiber connectors by resonant ultrasound spectroscopy (RUS). The ferrules were cylinders 10 mm in length and 2.5 mm in diameter. The acceptable ferrules had no cracks or ones below 5 μm and the defective ferrules had cracks from 5 to 25 μm in length. The acceptable ferrules could be distinguished from the defective ones statistically, even those with cracks of 5 μm, by comparing the differences between the resonant frequencies for both specimens.

Spin tunnel junction recording head

Micro-cracks in a magnetized ferromagnetic material cause stray fields that can be observed using giant magnetoresistive (GMR) sensors. This work investigates the applicability of GMR sensors to the non-destructive evaluation of micro-cracks via the observation of stray fields. For this purpose, our measurement setup is assessed using a fast new sensitivity analysis based on adjoint states, employing the finite-element method. A model for the GMR sensor is developed and verified. We are able to resolve micro-cracks with an opening of 3 μm and a depth of 30 μm. GMR positioning inaccuracies are analyzed.

Statistical Evaluation of Microcracking of Inelastic Ceramics

The model of fracture applicable to multiphase brittle materials, ceramics in particular, is developed. The model was used to solve the physical problem of describing the mechanical behavior of inelastic ceramics as a stochastic process of cracking of their structural components. The model can be useful for describing the mechanical behavior of single-phase ceramics with different statistical grain size distributions. The concept of effective medium and the statistical description of a fracture process were applied. Calculation results agree well with acoustic emission data.

Microcracking and chloride permeability of concrete under uniaxial compression

In the previous studies on microcracks and rapid chloride permeability tests, microcracks were quantified in terms of total crack length. This was carried out by examining concrete slices after compression tests. No attempts have been made to characterise the microcracks during the compression test prior to the chloride permeability test. In the present study, concrete cylinders were loaded under uniaxial compression between 30% and 95% of the ultimate strength. A non-destructive method of microcrack evaluation was used to study the progressive microcracking in concrete cylinders during compression tests. After the compression test, a rapid chloride permeability test (RCPT) (ASTM C1202) was carried out on a specimen cut from the same cylinder. The total crack length was also determined from the same specimen to compare with the observed microcracking behaviour, assessed by the non-destructive testing. The characteristics of the microcracks in terms of the specific crack area are different when a concrete is under a load and when it is completely unloaded. The chloride permeability of a concrete (after it was unloaded) appears to be influenced by the occurrence of a certain stress level known as the critical stress. When the critical stress is exceeded in a concrete specimen, a comparatively large chloride permeability was measured. Where the critical stress in a specimen is not exceeded, the increase in the permeability is marginal in spite of the large increase in microcracks.

Effects of Ultrasonic Root-End Preparation on Microcrack Formation and Leakage

Root-end preparations made with conventional ultrasonic (CUS) tips, diamond-coated ultrasonic (DUS) tips, and high-speed stainless-steel burs (HSB) were compared for the incidence of microcracks and dye leakage. One hundred twenty incisors were instrumented, obturated, and had 3 mm resected from their apices. Sixty teeth were used for microcrack evaluation before and after root-end preparation with CUS, DUS, or HSB. Three types of microcracks were observed: intracanal, extracanal, and communicating. Four of the five cracks observed after root resection (before root-end preparation) were of the extracanal or intracanal type. After root-end preparation, 19 of the 41 new microcracks that developed were the communicating type. There was no significant difference among CUS, DUS, or HSB for the number or type of cracks. Of the remaining 60 resected teeth, 25 were prepared with DUS, 25 with CUS, and 10 served as controls. All of the DUS and CUS teeth were filled with Super-EBA. Dye penetration was measured after immersion in Pelikan ink for 5 days. The dye penetration difference between DUS and CUS was not significant.

Nondestructive Evaluation of Microcracks in Ceramics with Controlled Probability of False Alarm

In this paper we present a complete detection scheme for ultrasonic crack detection in wet ceramics by means of ultrasonic nondestructive techniques. The detection scheme is based on a previous statistical characterization of the ultrasonic grain noise. In these previous works we obtained that the ultrasonic grain noise can be modeled as a K-noise [1, 2]. From this characterization we will prove that the expression of the probability of false alarm (PFA) obtained for a detector of Gaussian envelope pulses over K-noise using the Wigner-Ville Transform (WVT) proposed in reference [3] is valid for the real problem of ultrasonic microcrack detection in wet ceramics.

Nondestructive Evaluation of Microcracks in Ceramics with Controlled Probability of False Alarm

Nondestructive Evaluation of Microcracks in Ceramics with Controlled Probability of False Alarm

Nondestructive Evaluation of Microcracks in Ceramics with Controlled Probability of False Alarm

In this paper we present a complete detection scheme for ultrasonic crack detection in wet ceramics by means of ultrasonic nondestructive techniques. The detection scheme is based on a previous statistical characterization of the ultrasonic grain noise. In these previous works we obtained that the ultrasonic grain noise can be modeled as a K -noise [1, 2]. From this characterization we will prove that the expression of the probability of false alarm (PFA) obtained for a detector of Gaussian envelope pulses over K -noise using the Wigner-Ville Transform (WVT) proposed in reference [3] is valid for the real problem of ultrasonic microcrack detection in wet ceramics.

特集 応用地質における画像処理・解析 画像処理による微細な割れ目の抽出と評価 風化した花こう岩と一軒圧縮試験を行った安山岩における微細な割れ目の解析

特集 応用地質における画像処理・解析 画像処理による微細な割れ目の抽出と評価 風化した花こう岩と一軒圧縮試験を行った安山岩における微細な割れ目の解析

A new method for microcrack evaluation in concrete under compression

A method based on measurements of axial and transverse strains was developed for evaluation of the extent of microcracking in prismatic concrete specimens under uniaxial compression. The increase in the area of crack per unit cross-sectional area, which has the units of strain, was estimated from the transverse and axial strain measurements using a simple formula which involves the elastic Poisson’s ratio, determineda priori from the strain data.

Ultrasonic evaluation of microcracks in composites : Dayal, V.; Iyer, V.; Kinra, V.K. Proceedings of the 7th international conference on fracture (ICFY), Houston, Texas (United States), 20–24 March 1989. Spons. International Congress on fracture, pp. 3291–3300 (1989)

Ultrasonic evaluation of microcracks in composites : Dayal, V.; Iyer, V.; Kinra, V.K. Proceedings of the 7th international conference on fracture (ICFY), Houston, Texas (United States), 20–24 March 1989. Spons. International Congress on fracture, pp. 3291–3300 (1989)

Evaluation of microcracking in A533B steel by an acoustic emission source wave analysis.

Using a six-channel recording system, acoustic emission signals during fracture toughness testings of ASTM A533B steel were detected, located and characterized. Two samples of A533B steel with different sulfur content (medium sulfur sample : 0.013% S, low sulfur sample : 0.003% S) were prepared, and the AE characteristics were compared. In the medium sulfur sample whose fracture toughness is less than that of the low sulfur sample, two types of AE signals were detected. One was a signal due to microcracking at the MnS inclusion, and the other was a signal due to coalescence of the voids. In the low sulfur sample, only the former type of AE signals were detected, which means that, in this experiment, coalescence of the voids did not occur in the low sulfer sample because of its high fracture toughness. The results of the source wave analysis showed that microcracking at the inclusions was due to mode I type tension cracks with sizes of 10∼30 μm, and the coalescence of the voids was due to tension shear mixed cracks with sizes of 60∼100 μm.

Evaluation of microcracks by AE source characterization and fracture resistance in Al2O3 ceramics.

Low noise AE waveform analyzing system, especially for ceramics, was established and microcracks nucleated during fracture toughness testing of Al2O3 were evaluated using this system. Three dimensional locations of microcracks were carried out using arrival time difference of 6 ch AE waveform signals. In the earlier stage, microcracks were nucleated around the center of notch front, and in the latter stage, their sites were widened through the specimen thickness. Most of these cracks were evaluated as mode I cracks because of the same phase radiation pattern of AE signals detected. Furthermore, the quantitative sizes of there microcracks were estimated as 15-50 μm by AE source characterization. Consequently, after being evaluated these microcracks were classified into two groups based on their sizes, i.e. smaller (15-30 μm) and larger (30-50 μm) cracks. It was concluded that the former were effective microcracks used to enhance the fracture resistance of ceramics, while the latter became the origin for the final unstable fracture.