Effect Of Side Grooves Research Articles

Crack growth stabilization in the eccentric three-point end-notched flexure test of solid wood using side-grooved samples

A three-point eccentric end-notched flexure (3EENF) test was conducted on Sitka spruce to characterize the Mode II resistance curve (R-curve). To extend the range for stabilized crack growth, grooves were cut along both side surfaces of the sample to reduce the region around the neutral axis. The R-curve was determined by varying the initial crack lengths, and fracture toughness values were measured at both the onset and during growth. Additionally, the effect of side grooves on stabilizing crack growth in the 3EENF test was investigated by comparing numerical simulation results with those from four-point end-notched flexure (4ENF) tests. The grooves effectively stabilized crack growth, and the stabilization range was equivalent to that of the 4ENF test when the initial crack length was appropriately determined. The grooved sample exhibited behavior indicative of a longer crack than the actual length.

Miniature C(T) Specimens—Pinhole Eccentricity and the Effect of Crack Opening Displacement Measurement Location

AbstractThis paper focuses on the quality criteria for miniature compact tension (C(T)) specimens. The continuously diminishing volume of reference materials for fracture toughness surveillance testing encourages research on the usability of miniature-sized test specimens, and consequently, it is of great interest in the nuclear power plant field. Sufficient quality criteria and applicability are investigated experimentally and numerically by varying the pinhole locations to investigate the importance of the eccentricity of pinholes and its effect on measurement results. Additionally, the effect of measuring the crack opening displacement (CMOD) from the load line versus the front face and the effect of side grooving are studied with experimental arrangements. The results show that neither the eccentricity of pinholes within the studied offset values nor the location of the CMOD gauge imposes limits on the applicability of miniature C(T) specimens. With eccentric pinholes or any CMOD gauge placement, the fracture toughness results are valid.

Analysis of crack-tip constraint due to V- and U- side grooves in C(T) specimens

The effect of side grooves in standard compact tension (C(T)) specimens on the constraint due to plasticity under small scale yielding is presented in this paper. The Elastic-plastic crack-tip stress state is analysed through three dimensional finite element method. Ramberg-Osgood model is used to characterize the smooth transition of elastic-plastic behavior at the onset of crack-tip under Small Scale Yielding. Side grooves of type V and U are analysed and compared with plain specimen. Generally, it is observed that the plane stress effect on the surface of the plain specimen is restricted by the introduction of the side grooves. And this effect is studied with the in-plane crack-tip constraint parameter Q and out-of-plane constraint parameters Tz and h through the specimen thickness. It is found that localized plastic deformation at the side grooves increases the constraint level of the cracked specimen at the side grooves whereas it shows less at the middle of the specimen. It is also concluded that compared with U- groove specimen, V- groove specimen shows better constraint level.

Effect of Side Grooves on Plane Stress Fracture Behavior of Compact Tension Specimens Made of Ultra-High Strength Steel

Thin compact tension specimens made of direct quenched ultra-high strength steel were tested under constant rate uniaxial tensile load. The length of the crack was monitored using optical microscopes on both sides of the specimens during the fatigue pre-cracking (using a chevron V-notch). Deformations during the crack lengthening were recorded by a full-field measurement technique using a set of digital cameras to check the effect of side grooves on reduction of surface deformation. The Specimen without side grooves showed a high level of plasticity, thickness reduction, and crack growth along a deviating path. In addition, the fracture surface showed excessive failure along the inclined plane. The presence of side grooves, however, led to the decrease of the maximum applied force at final fracture while the force prior to crack tearing was almost the same as the specimen without side grooves. Grooves significantly reduced the inclination of the fracture plane and plastic deformation due to removal of low stress triaxiality on the surface. They led to the fracture along a straight path and approximately even surface which makes them beneficial especially when compliance method is used in plane stress fracture tests.

LBB 평가를 위한 J-R 파괴인성시험 결과에 미치는 시편 형상과 측면 홈의 영향

In this study, the effects of specimen size and side-groove on the results of the J-R test for leak-before-break (LBB) evaluation were investigated. A series of J-R tests were conducted at both RT and 316 o C, using three different sizes of compact tension (CT) specimens machined from SA508 Gr.1a piping material: 12.7 mm-thick 1T-CT, 25.4 mm-thick 1T-CT, and 25.4 mm-thick 2T-CT with and without side-groove. The results showed that side-grooving reduced the J-R curve for all specimens and the effect of side-grooving was more significant at 316 o C than at RT. As the thickness of the specimens decreased and the width of the specimens increased, the J-R curve slightly decreased at RT but it increased at 316 o C. However, the variation in the J-R curve of SA508 Gr.1a with the thickness and width of CT specimen was insignificant.

Testing and modelling of creep crack growth in compact tension specimens from a P91 weld at 650°C

Abstract Creep crack growth tests were performed, at 650 °C, on compact tension (CT) specimens machined from the parent material and from the weld region of a P91 weldment. Parent material tests were performed on a number of different CT specimen designs in order to investigate the effects of side grooves on the shape of the crack front. Tests of CT specimens machined from the weld region were performed with the initial cracks located within the heat-affected zone (HAZ) along the interface with the parent material (i.e. the type IV position). All of the specimens were prepared with initial cracks created by wire spark erosion. Good correlations between creep crack growth rates and C ∗ were obtained for both the parent and type IV test results. The results indicate that the crack growth rates in the weld specimens are about four times higher than those of the parent material specimens, at the same C ∗ . Microstructural investigations of the fracture surfaces using SEM and hardness measurements have shown that the exact location of the initial crack within the weldment has a large effect on the crack growth rate, at various loading levels. The results of Finite Element (FE) analyses of the parent material specimen tests, using a creep continuum damage material model, compared favourably with those obtained from the experiments.

C-Specimen Fracture Toughness Testing: Effect of Side Grooves and η Factor

Elastic-plastic crack front fields in arc-shaped tension specimens (C-specimens) were analyzed by a three-dimensional finite element method. The effect of side grooves on the ductile fracture behavior was investigated by studying the J-integral distribution, plane-strain constraint parameter, and development of plastic zones and comparing to experimental data. The applicability of the η factor (derived for use with compact tension specimens) for the calculation of J-integral values for the C-specimen was also investigated. The results show that side grooves promote and establish near plane strain conditions at the crack front in sub-size specimens. It was also found that a two-dimensional plane-strain analysis in conjunction with the standard American Society for Testing and Materials (ASTM) tests was sufficient to determine the fracture toughness values from side-grooved C-specimen. The results indicate the η factor for compact tension specimen as specified in the ASTM standards appears to produce reliable results for the calculation of J of C-specimens.

５０８３アルミニウム合金の衝撃吸収エネルギーとサイドグルーブ

Effects of side groove on the absorbed energy of the 5083 aluminum alloy were studied by Charpy impact test at 77K. Relations between the side groove and the laminated fracturing behaviors were also investigated. The results obtained are summarized as follows; (1) Absorbed energy of V and U type side groove specimens decreases as the side groove depth increases. The absorbed energy of V type side groove specimen is lower than that of U type specimen. (2) The growth of the laminated cracks of the side groove specimens is constrained effectively in the vicinity of the specimen ligament. (3) Six point height, which is closely related to the extent of the laminated cracks, decreases with increasing side groove depth for the V and U type side grooved specimens. Number of laminations, however, are not effected by the side groove depth.

Statistical analysis of the effect of side-grooving on the measurement of brittle fracture toughness

Fracture mechanics specimens are commonly side-grooved to promote uniformity of the crack tip stress field, but this practice may affect the fracture toughness measured because of changes in the net thickness and in the constraint. This study, based on Weibull statistics, shows that, for brittle fracture, the difference between the fracture toughness measured with plain-sided and 20 percent side-grooved specimens results essentially from the difference in net thicknesses. It is also shown that the effect of constraint should not be evaluated from the load arrying capacity of the specimen, but rather from the distribution of stress intensity factor along the crack front.

On the equivalent thickness of a side-grooved specimen.

Fracture toughness tests of side-grooved specimens were carried out to investigate the equivalent thickness of a side-grooved specimen. The effects of side-groove on stretched zone width and stable crack growth were also investigated. From the results, the equivalent thickness for the JIC-value will be in the range between Be1(=B·BN) and Be2(=B-(B-BN)2/B). Although the thickness Be2 can be utilized from the viewpoint of conservative estimations, it is reasonable to use the thickness Be1 which also gives good estimations for the blunting line.

The thickness effects of the side-grooved CCT specimen. 1st report Fracture toughness of SUS316 steel.

JIC tests were carried out on SUS 316 steel by means of the JSME R-curve method as well as the JSME stretched-zone width (SZW) method. The effect of side-grooves on the Jin value at stable crack growth initiation was investigated by using CCT specimens of two thicknesses (B=1, 2mm). The ratio of net thickness to gross thickness was kept at 0.5. The Jin values of the side-grooved CCT specimens of two thicknesses were considerably smaller than those of the 1TCT specimen. The Jin value of the side-grooved specimen of 2mm thickness was smaller than that of the standard CCT specimen. Further, as the thickness of the specimen becomes thinner, the Jin value decreases. In the case of 1mm thick CCT specimens with or without a side groove, the contraction percentage of thickness is very large so that it is not appropriate to use these specimens for the fracture toughness test. In the case of the thin or side-grooved CCT specimen, the J value which is evaluated from the load versus displacement curve by using Rice's formula cannot estimate the J-integral at the central part of the specimen. Therefore, a J-integral estimation method would have to be established by using 3-D elasto-plastic analysis.

Effect of Side Grooves for Three-point Bending Fracture Toughness Specimens : Three-dimensional Elastic-plastic Finite Element Analysis

Elastic-plastic stress states on three-point bending fracture toughness specimens are analyzed by the three-dimensional finite element method. Effect of side grooves on the stress state around the crack tip is discussed on specimens about 30 % side-grooved in U, V, and slit types comparing with a regular flat specimen. Side grooves restrict the plane stress type deformation, which is commonly observed near the side face of a flat specimen. Consequently, over 80-90 % of the thickness of the side-grooved specimens, practically even distributions of the stress intensity factors, plastic zone geometries, crack tip dilatant stresses, and three-dimensional J integrals are achieved.

Effect of side grooves on the elastic-plastic stress state of fracture toughness specimens—three-dimensional finite element analysis

Elastic-plastic stress states on double-edge-notched tensile specimens are analyzed by the three-dimensional finite element method. Effect of side grooves on the stress state around the crack tip are discussed on specimens about 30% side-grooved in U, V and slit types comparing with a regular flat specimen. On the flat specimen, the plastic zone develops extensively near the free surface but the dilatant stress there does not increase so much as at middle region. Accordingly, differences of the plastic zone size and the stress through the thickness increase with increasing the load. Although the side groove promotes the severe plastic deformation over limited region near the root of the groove, practically even distributions of the plastic zone and the dilatant stress can be resulted on V-grooved and slitted specimens.

Determination of the Fracture-Energy Criterion JIc of Two Steels by Static and Dynamic Testing

Abstract The fracture energy criterion JIc was determined on two carbon-manganese steels, SA-516-70 and SA-105-B, from a single specimen. A graphic method is proposed for verifying the validity of measured values of JIc. Static JIc and dynamic JIcD experiments on precracked Charpy V-notch specimens at ambient temperature enabled the observation of the effect of loading rate on the value of JIc. For these two steels, the effect of side grooves was detected only in dynamic testing. For SA-516-70 steel, JIcD > JIc, while JIcD > JIc for SA-105-B steel, because of transition temperature fracture behavior. For SA-516-70, static testing was performed on three-point bend specimens of different dimensions to determine the effect of geometrical parameters on the value of JIc. A ligament 1-cm long is the lower limit for the determination of JIc.

Application of compliance techniques for studying the effect of side-grooving on stress-corrosion crack kinetics of a high strength steel

Abstract : Sub-critical crack growth was estimated from changes in compliance measured during the stress-corrosion cracking of D6AC steel at constant load using 1-T wedge-opening-loading specimens. Agreement of calculated mean crack growth with mean values measured from the fracture surface showed that plastic yielding at the crack tip during loading and subsequent stress-corrosion cracking was negligible. The analysis was then applied to side-grooved specimens where it was demonstrated that, under plane-strain conditions, side-grooving does not significantly affect the stress-corrosion cracking rate in D6AC steel.

Effect of side-grooving on the compliance of the cantilever bend specimen

The precracked cantilever bend specimen, which is normally employed to determine the stress corrosion cracking threshold K Iscc , can also be used to obtain the stress corrosion crack growth rate as a function of stress intensity factor K I . When the crack is obscured, crack growth can be monitored by measuring the crack-opening displacement and converting this to crack length by means of the compliance relationship for the specimen. Compliance relationships were therefore determined for 0.5-in.-thick AISI 4340 steel cantilever bend specimens with net-to-gross thickness ratios of 1.0 (no side grooves), 0.8(shallow side grooves), and 0.6 (deep side grooves). The shallow side grooves had no effect on the crack-opening compliance relationship, while the deep side grooves increased the crack-opening compliance by about 20%.

Effects of side grooves on initiation and propagation of ductile fracture

AbstractThe use of side grooves in determining critical crack opening displacement values in small notch bend specimens is discussed. The critical crack opening displacement for fully ductile behaviour δmax. is seen to decrease to a constant value with increasing side-groove depth. This value of δmax. is found to coincide with the crack opening displacement for the initiation of fibrous fracture δ1 determined on non-side-grooved specimens. The effect of deep side grooving is considered to be one of promoting through-thickness plane strain conditions in specimens normally too thin for this behaviour to be observed. The use of appropriately side-grooved specimens is considered to be a reliable and effective method of determining δ1.