Reference point indentation is not indicative of whole mouse bone measures of stress intensity fracture toughness

This paper presents the results of the fracture toughness of concretes containing two mineral additives. During the tests, the method of loading the specimens according to Mode I fracture was used. The research included an evaluation of mechanical parameters of concrete containing noncondensed silica fume (SF) in an amount of 10% and siliceous fly ash (FA) in the following amounts: 0%, 10% and 20%. The experiments were carried out on mature specimens, i.e., after 28 days of curing and specimens at an early age, i.e., after 3 and 7 days of curing. In the course of experiments, the effect of adding SF to the value of the critical stress intensity factor—KIcS in FA concretes in different periods of curing were evaluated. In addition, the basic strength parameters of concrete composites, i.e., compressive strength—fcm and splitting tensile strength—fctm, were measured. A novelty in the presented research is the evaluation of the fracture toughness of concretes with two mineral additives, assessed at an early age. During the tests, the structures of all composites and the nature of macroscopic crack propagation were also assessed. A modern and useful digital image correlation (DIC) technique was used to assess macroscopic cracks. Based on the conducted research, it was found the application of SF to FA concretes contributes to a significant increase in the fracture toughness of these materials at an early age. Moreover, on the basis of the obtained test results, it was found that the values of the critical stress intensity factor of analyzed concretes were convergent qualitatively with their strength parameters. It also has been demonstrated that in the first 28 days of concrete curing, the preferred solution is to replace cement with SF in the amount of 10% or to use a cement binder substitution with a combination of additives in proportions 10% SF + 10% FA. On the other hand, the composition of mineral additives in proportions 10% SF + 20% FA has a negative effect on the fracture mechanics parameters of concretes at an early age. Based on the analysis of the results of microstructural tests and the evaluation of the propagation of macroscopic cracks, it was established that along with the substitution of the cement binder with the combination of mineral additives, the composition of the cement matrix in these composites changes, which implies a different, i.e., quasi-plastic, behavior in the process of damage and destruction of the material.

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On notch fracture mechanics

Industrial laboratory Diagnostics of materials ◽

10.26896/1028-6861-2021-87-2-56-64 ◽

2021 ◽

Vol 87 (2) ◽

pp. 56-64

Author(s):

G. Pluvinage

Keyword(s):

Fracture Toughness ◽

Stress Intensity Factor ◽

Stress Intensity ◽

Intensity Factor ◽

Plastic Zone ◽

Fracture Resistance ◽

Notch Radius ◽

Notch Stress Intensity Factor ◽

Blunt Notch ◽

Notch Stress

Different stress distributions for an elastic behavior are presented as analytical expressions for an ideal crack, a sharp notch and a blunt notch. The elastic plastic distribution at a blunt notch tip is analyzed. The concept of the notch stress intensity factor is deduced from the definition of the effective stress and the effective distance. The impacts of the notch radius and constraint on the critical notch stress intensity factor are presented. The paper ends with the presentation of the crack driving force Jρ for a notch in the elastic case and the impact of the notch radius on the notch fracture toughness Jρ,c. The notch fracture toughness Jρ,c is a measure of the fracture resistance which increases linearly with the notch radius due to the plastic work in the notch plastic zone. If this notch plastic zone does not invade totally the ligament, the notch fracture toughness Jρ,c is constant. This occurs when the notch radius is less than a critical one and there is no need to use the cracked specimen to measure a lower bound of the fracture resistance.

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Fracture of Defects Approaching a Free Surface

Journal of Pressure Vessel Technology ◽

10.1115/1.3454307 ◽

1975 ◽

Vol 97 (4) ◽

pp. 270-277 ◽

Cited By ~ 4

Author(s):

W. G. Gibbons ◽

W. R. Andrews ◽

G. A. Clarke

Keyword(s):

Fracture Toughness ◽

Fatigue Crack ◽

Free Surface ◽

Stress Intensity ◽

Surface Stress ◽

Empirical Equation ◽

Near Surface ◽

Fracture Characteristics ◽

Testing Program ◽

Measured Strain

A testing program has been run using off-centered-cracked (OCC) plate specimens to demonstrate the fracture characteristics of tunnel defects in specimens with various ligament lengths between the near surface crack tip and a free surface. Measured strain values and the fracture results compared favorably with theory up to the limits of the analyses. An empirical equation which calculates the near surface stress intensity provides extended calculational capabilities. In addition, fatigue crack growth and fracture velocities plus fracture toughness were measured for a Cr-Mo-V steel.

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

Cellulose ◽

10.1007/s10570-021-04237-3 ◽

2021 ◽

Author(s):

C. Fernández-Diego ◽

I. A. Carrascal ◽

A. Ortiz ◽

I. Fernández ◽

D. Ferreño ◽

...

Keyword(s):

Fracture Toughness ◽

Stress Intensity Factor ◽

Stress Intensity ◽

Intensity Factor ◽

Dielectric Materials ◽

Superior Performance ◽

Mechanical Resistance ◽

Insulation Material ◽

Cellulose Materials ◽

Over Time

AbstractOil-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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Effect of Slag Particle Size on Fracture Toughness of Concrete

Applied Sciences ◽

10.3390/app9040805 ◽

2019 ◽

Vol 9 (4) ◽

pp. 805 ◽

Cited By ~ 3

Author(s):

Chung-Ho Huang ◽

Chung-Hao Wu ◽

Shu-Ken Lin ◽

Tsong Yen

Keyword(s):

Fracture Toughness ◽

Particle Size ◽

Compressive Strength ◽

Stress Intensity ◽

Fracture Energy ◽

Critical Stress ◽

Critical Stress Intensity Factor ◽

Cementitious Material ◽

Test Results ◽

Unique Effect

The effects of particle size of ground granulated blast furnace slag (GGBS) on the fracture energy, critical stress intensity, and strength of concrete are experimentally studied. Three fineness levels of GGBS of 4000, 5000, 6000 cm2/g were used. In addition to the control mixture without slag, two slag replacement levels of 20% and 40% by weight of the cementitious material were selected for preparing the concrete mixtures. The control mixture was designed to have a target compressive strength at 28 days of 62 MPa, while the water to cementitious material ratio was selected as 0.35 for all mixtures. Test results indicate that using finer slag in concrete may improve the filling effect and the reactivity of slag, resulting in a larger strength enhancement. The compressive strength of slag concrete was found to increase in conjunction with the fineness level of the slag presented in the mixture. Use of finer slag presents a beneficial effect on the fracture energy (GF) of concrete, even at an early age, and attains a higher increment of GF at later age (56 days). This implicates that the finer slag can have a unique effect on the enhancement of the fracture resistance of concrete. The test results of the critical stress intensity factor (KSIC) of the slag concretes have a similar tendency as that of the fracture energy, indicating that the finer slag may present an increase in the fracture toughness of concrete.

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Numerical computation of dynamic stress intensity factor for impact fracture toughness test.

The Journal of the Japan Society of Aeronautical Engineering ◽

10.2322/jjsass1969.36.147 ◽

1988 ◽

Vol 36 (410) ◽

pp. 147-154

Author(s):

Motohiro NAKANO ◽

Keizo KISHIDA

Keyword(s):

Fracture Toughness ◽

Stress Intensity Factor ◽

Stress Intensity ◽

Intensity Factor ◽

Numerical Computation ◽

Dynamic Stress ◽

Dynamic Stress Intensity Factor ◽

Impact Fracture ◽

Fracture Toughness Test ◽

Toughness Test

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Microhardness distribution of the tibial diaphysis and test site selection for reference point indentation technique

Medicine ◽

10.1097/md.0000000000016523 ◽

2019 ◽

Vol 98 (29) ◽

pp. e16523 ◽

Cited By ~ 1

Author(s):

Jianzhao Wang ◽

Bing Yin ◽

Guobin Liu ◽

Sheng Li ◽

Xiaojuan Zhang ◽

...

Keyword(s):

Site Selection ◽

Reference Point ◽

Test Site ◽

Indentation Technique ◽

Tibial Diaphysis ◽

Microhardness Distribution ◽

Reference Point Indentation ◽

Selection For

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