In-Plane Fracture Toughness Measurement of Paper

Mai, Yiu‐Wing; He, Herman; Leung, Roy; Seth, R. S.

doi:10.1520/stp16407s

Cited by 8 publications

(5 citation statements)

References 17 publications

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“…2) with different notch sizes, were tested in tension. Following the recommendations of previous authors (Mai et al 1995;Chen et al 2016;Mao et al 2017) the ligaments of the specimens in this research are in the range 6 mm B b 0 B 8 mm, with specimen width (2 W) of 15 mm. Each specimen's ligament was measured using an optical device coupled to a three-dimensional coordinate measuring machine (TESA MICRO-HITE 3D).…”

Section: Fracture Toughnessmentioning

confidence: 95%

“…When a test fails to meet the thickness and other test requirements that are in place to ensure plane strain conditions, the fracture toughness value produced is denoted K Q instead of K Ic . The fracture process zone in a piece of paper corresponds to the region just ahead of the crack tip, where the fiber breakage and bond breakage concentrate when a cracked specimen is strained (Mai et al 1995).…”

Section: Fracture Toughnessmentioning

confidence: 99%

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Fracture toughness as an alternative approach to quantify the ageing of insulation paper in oil

et al. 2021

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Oil-immersed transformers use paper and oil as insulation system which degrades slowly during the operation of these machines. Cellulose materials are used generally as insulation solid in power transformers. The degree of polymerization (DP), defined as number of repeating β-glucose residues in the cellulose molecule, is a critical property of cellulosic insulation material used in transformers, since it provides information about paper ageing and its mechanical strength. The fast-developing electric power industry demanding superior performance of electrical insulation materials has led to the development of new materials, as well as different drying techniques performed during transformer manufacturing and service when required. Both developments have caused some practical difficulties in the DP measurement. Moreover, the increasing interest in synthetic dielectric materials replacing cellulose materials requires measuring alternative properties to the DP to quantify the degradation of insulation solids over time. In this sense, this paper proposes the possibility of analyzing paper degradation through fracture toughness. This approach is different from the study of mechanical properties such as tensile strength or strain because it provides a tool for solving most practical problems in engineering mechanics, such as safety and life expectancy estimation of cracked structures and components which cannot to be considered through the traditional assessment of the mechanical resistance of the material. An accelerated thermal ageing of Kraft paper in mineral oil was carried out at 130 °C during different periods of time, to obtain information on the kinetics of the ageing degradation of the paper. Double-edged notched specimens were tested in tension to study their fracture toughness. The evolution of the load–displacement curves obtained for different ageing times at the ageing temperature of 130 °C was utilized to the determination of the stress intensity factor. Furthermore, different kinetic models based on this stress intensity factor were applied to relate its evolution over time as a function of the temperature. Finally, the correlation between the DP and stress intensity factor, which depends on the fiber angle, was also defined. Graphic abstract

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Section: Fracture Toughnessmentioning

confidence: 95%

Section: Fracture Toughnessmentioning

confidence: 99%

Fracture toughness as an alternative approach to quantify the ageing of insulation paper in oil

et al. 2021

View full text Add to dashboard Cite

show abstract

“…2) with different notch sizes, were tested in tension. Following the recommendations of previous authors (Mai et al 1995;Chen et al 2016;Mao et al 2017) the ligaments of the specimens in this research are in the range 6 mm ≤ b 0 ≤ 8 mm, with specimen width (2W) of 15 mm. Each specimen's ligament was measured using an optical device coupled to a three-dimensional coordinate measuring machine (TESA MICRO-HITE 3D).…”

Section: Fracture Toughnessmentioning

confidence: 96%

“…When a test fails to meet the thickness and other test requirements that are in place to ensure plane strain conditions, the fracture toughness value produced is denoted K c . The fracture process zone in a piece of paper corresponds to the region just ahead of the crack tip, where the ber breakage and bond breakage concentrate when a cracked specimen is strained (Mai et al 1995). Fracture toughness test were conducted following the K Ic procedure of the standard ASTM E1820-01.…”

Section: Fracture Toughnessmentioning

confidence: 99%

Fracture Toughness As An Alternative Approach To Quantify The Ageing of Insulation Paper In Oil

Fernández-Diego

Carrascal

Ortiz

et al. 2021

Preprint

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Oil-immersed transformers use paper and oil as insulation system which degrades slowly during the operation of these machines. The fast-developing electric power industry demands superior performance of electrical insulation materials which has led to the development of new materials whose measurement of the degree of polymerization has found some practical difficulties. Moreover, the increasing interest in synthetic dielectric materials replacing cellulose materials requires the use of alternative methods to the degree of polymerization to quantify the degradation of insulation solids over time. In this sense, this paper proposes the possibility of analyzing paper degradation through fracture toughness. An accelerated thermal ageing of Kraft paper in mineral oil was carried out at 130ºC during different periods of time, to obtain information on the kinetics of the ageing degradation of the paper. Double-edged notched specimens were tested in tension to study their fracture toughness. The evolution of the load-displacement curves obtained for different ageing times at the ageing temperature of 130°C was utilized to the determination of the stress intensity factor. Furthermore, different kinetic models based on this stress intensity factor were applied to relate its evolution over time as a function of the temperature. Finally, the correlation between the DP and stress intensity factor, which depends on the fiber angle, was also defined.

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“…Many kinds of mechanical parameters, such as elastic properties, strength, fracture energy, fracture toughness, and post-peak stress-strain curve, are found to be dependent on the size of specimen. For examples, Mai et al (1980) investigated the size effects on fracture load, fracture stress and strain energy density in an asbestos-cellulose cement composite using three point notched bend beams with geometrically scaled dimensions [2]; found that the slope of J Rcurve may be affected by specimen size and geometry effects [3]; Mai (1985) presented the effects of specimen size, geometry and environment on R-curve; Wu and Mai (1996) found that the specific essential work of fracture is a material constant independent of sample geometry, and equivalent to the critical J-integral [4]; Jin and Mai (1995) investigated the size-dependence of thermal shock strength behavior [5]; Cottrell and Mai (1987) used the crack growth resistance curves to explain the specimen size and crack length dependence of fracture toughness in cement pastes [6]; Shah (1990) proposed a size-effect method for determining the fracture energy of concrete by measuring the maximum loads of geometrically similar notched concrete specimens of different sizes [7]; Duan et al (2002) explained the size effect in concrete fracture using nonuniform energy distribution [8]; Bažant and Kazemi (1990) analyzed the dependence of the fracture energy on the specimen size on the basis of Bažant's size effect law [9]; Ji et al (1997) explained the size effect of fracture energy of cement-based materials and a relationship between fracture energy and height of the ligament of specimen was established [10]; Guo and Gilbert (2000) introduced the concept of partial fracture energy to explain the observed size effect [11].…”

Section: Introductionmentioning

confidence: 99%

Size Effect of Shear Fracture Energy of Concrete in Uniaxial Compression Based on Gradient-Dependent Plasticity

Wang

2006

KEM

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Gradient-dependent plasticity where a characteristic length is involved into yield function is adopted to calculate the thickness of shear band (SB) and the distribution of plastic shear strain in SB. The characteristic length reflecting the heterogeneous extent of texture only controls SB’s thickness. The local plastic shear strain in SB is highly non-uniform. The total fracture energy is the sum of pre-peak and post-peak fracture energies. The pre-peak part is described by the nonlinear Scott model and depends on the height of specimen. The post-peak part is calculated through the derived post-peak relative stress-plastic deformation curve. If the inclination angle of SB is not influenced by the height, then the slope of post-peak relative stress-plastic deformation curve and the post-peak fracture energy are independent of the height. The total fracture energy is linearly size-dependent as the pre-peak fracture energy is linearly related to the height. The slope of postpeak relative stress-plastic deformation and the total fracture energy are verified through previous experiments for normal concrete in uniaxial ompression.

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In-Plane Fracture Toughness Measurement of Paper

Cited by 8 publications

References 17 publications

Fracture toughness as an alternative approach to quantify the ageing of insulation paper in oil

Fracture toughness as an alternative approach to quantify the ageing of insulation paper in oil

Fracture Toughness As An Alternative Approach To Quantify The Ageing of Insulation Paper In Oil

Size Effect of Shear Fracture Energy of Concrete in Uniaxial Compression Based on Gradient-Dependent Plasticity

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