An investigation of propagating cracks by dynamic photoelasticity

Dynami c photoelasticity and dynamic finite element methods were used to study the transient response of dynamic tear test (DTT) specimen o~ a brittle materia l , Homa lite-lOO . The dynami c stress intensity factors obtained from dyna~ic photoelasticity and dynami c finite element analysis were generally in excellent agreement wi th each other and showed that the NRL procedure of computina the dynamic fracture initiation toughness from strain gage measurements near the crack tip was reasonably accurate . Dynami c fracture toughness versus crack velocity relations were also obtained. I NTRODUCT IONIn a previous paper [ 1], one of the authors used dynami c photoelasticity to analyze an enlarged photoelastic model of the dynamic tear test specimen (DTT) developed by the Naval Research Laboratories ( NRL) [2 ,3,4]. This DTT specimen , which is a dynamically loaded three-point bend specimen , developed ful l thickness cleavage fracture without sidegrooving and Is an ASIM proposed fracture specimen for assessing potential brittle fracture characteristics of ductile materials.Brittle fracture of the NRL type DTT specimen in the previous dynamic photoelasticity Investigation was modeled by 356x88.9 m specimens machined from 9.5 rv thick Homalite-lOO plates subjected to an Impact loading of 1.83 to 3.62 N-rn * Currently on l eave from Ta kasa go Technical Institute , Mi tsubishi Heavy Industries , Ta kasa go , Japan. 2. Dynami c fracture toughness, K IDS decreases after reaching a maximum value as the crack propagated towards the Impact site .3. Dynamic tear energy which was computed from the measured dynamic fracture toughness varied wi th the sharpness of the starter crack.4. The average dynami c energy release rate,~J D, was approximately equal to the critical strain energy release rate, b i~, of the Homalite-lOO plate.In a subsequent reevaluation of this DII test resul t [5], dynamic fracture initiation toughness , K Id, was estimated to be approximately equal to the static fracture toughness, K it , in contradiction with the generally expected decrease in K Id under Impact loading. Such possible decrease in K Id for the strain ratesensitive Homalite-lOO plates was conjectured from the observed trend in ductile metals with lesser strain rate sensitivity than Homalite-iQO plates.Results of the above dynamic photoelastic investigation presented some new concepts for the fracture dynamic response of DTT specimens as well as identified areas in which further investigation is necessary to clari fy points of controversy . As a result , in this study DTT specimens machined from Homalite-lOO plates were reanalyzed by dynamic photoelasticity as well as by the newly developed dynamic finite element method . The numerical technique was also used to compute the dynamic strains adjacent to the crack tip prior to and ininediately after the onset of crack propagation and the dynamic stress Intensity factor at the onset of crack propagation , K id, was then estimated through Loss static procedure ( 3].In the following so...

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“…A split Nopkinson bar system [ 7 ] with test specimens of 9.5x9.5x254 nins or 9.5x9.5x38l rims were used . …”

Section: Dtt Test Specimenmentioning

confidence: 99%

Dynamic photoelastic and dynamic finite-element analyses of dynamic-tear-test specimens

Mall

Kobayashi

Urabe

1978

Experimental Mechanics

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“…Irwin [2] used the equations of the stress field near the crack tip for Mode I to calculate the stress intensity factor from a single fringe data. Bradley and Kobayashi [3] modified the method of Irwin by using the values of the fringe order from two consecutive fringes. Schroedel and Smith [4] proposed the calculation of the stress intensity factor using the values of the fringe order on a line normal to the crack tip, method which was subsequently developed by Smith [5].…”

Section: Introductionmentioning

confidence: 99%

“…Schroedel and Smith [4] proposed the calculation of the stress intensity factor using the values of the fringe order on a line normal to the crack tip, method which was subsequently developed by Smith [5]. A methodology similar to that proposed in [3] was developed by Etheridge and Dally [6], which introduced a correction factor for the boundary effects in the expressions of the stress intensity factor. Chona et al [7] used the Westergaard stress field expressions, written as series expansion and obtained the coefficients of the expansion using photoelastic data.…”

Section: Introductionmentioning

confidence: 99%

Photoelastic Analysis of Cracked Thick Walled Cylinders

Pastramă

2017

ACTA Universitatis Cibiniensis

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“…instantaneous dynamic stress intensity factor, during crack propagation the dynamic stress intensity fact(.-, which is extracted from transient dynamic isochromatics surrounding the propagating crack tip, is used to measure the dynamic fracture toughness. A commonly used data reduction procedure for this purpose is to fit a theoretical, near-field, static isochromatics to the recorded experimental dynamic isochromatics and to then equate the resultant static stress intensity factor of the former to the unknown dynamic stress intensity factor of the latter [2][3][4][5]. Error estimates for using a static near-field stress to extract the dynamic stress intensity factor have been made by several investigators [6][7][8] and in particular, exhaustively by Rossmanith and Irwin [8].…”

Section: Introductionmentioning

confidence: 99%

Dynamic stress-intensity factors for unsymmetric dynamic isochromatics

Kobayashi

1981

Experimental Mechanics

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The mixed mode, near-field state of stresses surrounding a crack propagating at constant velocity is used to derive a relation between the dynamic stress intensity factors K i , KII, the remote stress component oox and the dynamic isochromatics. This relation together with an overdeterministic least-square method form the basis of a data reduction procedure for extracting dynamic K i , KII and ox from the recorded dynamic photoelastic pattern surrounding a running crack. The overdeterministic least-square method is also used to fit static isochromatics to the numerically generated dynamic isochromatics. The resultant static K I , KII, and aox are compared with the corresponding dynamic values and estimates of errors involved in using static analysis to process dynamic isochromatic data are obtained. The data reduction procedure is then used to evaluate the branching stress intensity factor associated with crack branching and the mixed mode stress intensity factors associated with crack curving.

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An investigation of propagating cracks by dynamic photoelasticity

Cited by 173 publications

References 7 publications

Dynamic photoelastic and dynamic finite-element analyses of dynamic-tear-test specimens

Dynamic photoelastic and dynamic finite-element analyses of dynamic-tear-test specimens

Photoelastic Analysis of Cracked Thick Walled Cylinders

Dynamic stress-intensity factors for unsymmetric dynamic isochromatics

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