Shear Type Fracture Research Articles

Effect of Hydrogen on Tensile Properties of Ultrafine-Grained Type 310S Austenitic Stainless Steel Processed by High-Pressure Torsion

This study addresses a hydrogen effect on the tensile properties of a type 310S austenitic stainless steel with ultrafine-grained structures produced by high-pressure torsion (HPT) and subsequent annealing. The mean grain size was reduced to ~85 nm by the HPT processing. The grain size was increased by the post-HPT annealing, but the grain size of ~265 nm was retained after annealing at 1023 K (750 °C). The tensile strength of ~1.2 GPa, which is approximately twice as much as that of the solution-treated specimen, was attained in the 1023 K (750 °C) post-HPT-annealed specimen. The elongation to failure was restored up to ~15 pct by the post-HPT annealing, although it was still insufficient in comparison with the ~55 pct elongation of the solution-treated specimen. There was no change in the tensile strength of the HPT-processed specimens and the post-HPT-annealed specimens by hydrogen charging with the hydrogen content in the range of ~20 to 40 mass ppm. The HPT-processed and the 773 K (500 °C) post-HPT-annealed specimens exhibited a ductility loss through the fully shear type fracture. The hydrogen charge into higher temperature post-HPT-annealed specimens with σ-FeCr precipitates led to a mild hydrogen embrittlement.

Hoop strength and ductility evaluation of irradiated fuel cladding

The objective of this study is to evaluate the hoop-directional mechanical properties comprising strength such as yield strength and ultimate tensile strength as well as mechanical ductility such as uniform elongation and total elongation. Therefore, in this paper, the ring tensile tests were performed in order to evaluate the mechanical properties of high burn-up fuel cladding under a hoop loading condition in a hot cell. The tests were performed with Zircaloy-4 nuclear fuel cladding whose burn-up is approximately 65,000 MWd/tU in the temperature range of room temperature to 800 °C. All the experiments were carried out at a constant strain rate of 0.01/s. On the basis of the ring tensile tests for a high burn-up Zircalay-4 cladding, the following conclusions were drawn. Firstly, the mechanical properties are abruptly degraded beyond 600 °C, which corresponds to a design-basis accident condition such as a RIA. Secondly, the un-irradiated fuel cladding showed ductile fracture behaviors such as 45° shear type fracture, cup and cone type fracture, cup and cup type fracture and chisel edge type fracture. While the high burn-up Zircalay-4 cladding showed a brittle fracture behavior even at the high temperatures (e.g. over 600 °C) which are achievable during a RIA. Thirdly, in the case of the high burn-up Zircalay-4 cladding, the strength, ductility and the energy to break are strongly dependent on the material property itself which are degraded by oxidation and hydriding during an operation rather than the temperature. Fourthly, hydride rim formation in the vicinity of metal–oxide interface can play an important role in the degradation of the mechanical properties for high burn-up fuel cladding.

Fracture of Magnesium Alloy in Cold Forging

In order to clarify the forming limit of magnesium alloy in cold forging, the workability of magnesium alloy AZ31B (Mg-3%Al-1%Zn) is examined by upsetting and backward extrusion. In the upsettability test, shear type fracture occurs at a small equivalent strain of about 0.15 at temperatures lower than 170 °C. At a higher temperature, the flow stress curve has a peak at an average equivalent strain of 0.2–0.3, showing a clear tendency to work soften. In cold backward extrusion with a conical punch, the local strain can reach a very large value, 3.0 or greater, without fracture. To explain the experimental results, the mechanism of fracturing is discussed on the basis of strain localization, and a fracture criterion of magnesium alloy in cold forging is suggested. The newly proposed criterion provides much better results than the existing criteria.

真空ダイカストならびに高速双ロールキャストしたアルミニウム合金の組織と引裂靭性

Vacuum die-cast and high-speed twin-roll cast products were fabricated using a heat-treatable Al-Si-Mg base alloy (A) and a non-heat-treatable Al-Mg base alloy (B). These alloys have almost equivalent tensile strength and ductility but different solidified structure. Tear toughness tests were performed using a small-size specimen and the unit crack propagation energy, UEp, was obtained from the load-displacement curve. For the vacuum die-cast products, both A and B exhibited macroscopically plane fracture surface. Dimple formation nucleated at the globular eutectic Si particles was detected in A. In contrast to that, the fracture surface of B was covered with a lamella eutectic structure. UEp was larger in A than B. Large increase in UEp was obtained for the twin-roll cast products. Their UEp values were 1.8 and 3 times larger than those of vacuum die-cast A and B, respectively. Macroscopic appearance of the twin-roll cast products was characterized by the slanted shear-type fracture path for both A and B. In addition to that, fracture surface of B showed fine dimple fracture surface. Large increase in UEp for B is due to the morphological change of the eutectic structure from the lamellar-type to the fine and globular-type induced by the rapid cooling rate of the high-speed twin-roll casting.

Prediction of Tensile-Shear Strength of Spot Welds Based on Fracture Modes

Assessment of the strength of spot welds is a key process in the design of spot welded structures. Moreover, the prediction method to be used to evaluate the strength of specimens is not always clear, even for static loading. This is because the strength of spot welds depends upon various factors such as nugget diameter, plate width and thickness, material strength, number and location of spot welds and different fracture patterns. In this study, three formulae were proposed for the prediction of the tensile-shear strength of spot welds, which are based upon the relationship between the maximum stress and material strength in three fracture modes; plug type fracture, shear type fracture and fracture across the base metal. In these formulae, two parameters were used for the assessment of maximum stress in the uneven stress distribution around a spot weld. Assuming that fracture takes place at the weakest portion of the structure, the tensile-shear strength is given by the minimum value of the fracture load evaluated for the three fracture modes. It was shown by comparing the predictions and experiments that the predicted fracture load and real fracture mode are in close agreement for both single- and multi-spot welds.

Evaluation of Ductile Fracture in Plastic Forming of Metal Sheet

It is significant to predict ductile fracture initiation in plastic forming of metal materials. Tube hidroforming (THF) is attracting general attention.THFprocess requires the control of internal liquid pressure and axial compression. In this case a ductile fracture may occur under stress triaxiality lower than that for uniaxial tension loading. In this report, combined longitudinal tensile and compression to thickness direction tests using thin plate specimens inA5083-Oaluminum alloy to obtain low stress triaxiality were carried out. On the basis of observations of ductile fracture processes it was founded that ductile fracture was shear type fracture controlled by a nucleation of micro-voids in this test. It is seemed that the local inclusion-matrix interfacial stress was constant independently of any stress ratio of tension and compression. Additionally, THFtests for SPFH590 tubes were performed. It was confirmed that the critical interfacial stress obtained using FE analysis forTHFtest was constant.

211 スポット溶接部材の強度と破断様式に及ぼす因子の検討(O.S.5 : 溶接・接合材の強度および力学的特性の評価)

In order to clarify the relation between strength and fracture mode, the tensile-shear test of spot welds and stress analysis has been done. The results showed that the bending moment and axial force induced by tensile-shear test affected 3 types of fracture modes (shear type fracture, plug type fracture and fracture across base metal), which depended upon the material properties, the specimen geometry, weld size, position and numbers of spot welds. As the results, the strength of spot weld changes with fracture mode.

Synthesis of High Strength Bulk Amorphous Zr–Al–Ni–Cu–Ag Alloys with a Nanoscale Secondary Phase

Bulk amorphous alloys in a cylindrical form were prepared in the diameter range up to about 5 mm for Zr 65 Al 7.5 Ni 10 Cu 17.5 - x Ag x (x=0 to 5 at%) by copper mold casting. These bulk amorphous alloys exhibit a wide supercooled liquid region before crystallization and the temperature interval defined by the difference between glass transition temperature (T g ) and crystallization temperature (T x ), ΔT x (= T x - T g ) is 111 K for the 0%Ag alloy and 63 K for the 5%Ag alloy. The replacement of Cu by 5 at%Ag causes the change in the crystallization process from a single stage of Am → Zr 2 (Cu, Ni) + Zr 2 (Al, Ni) to two stages of Am → Am' + Zr 3 (Al, Ag) 2 → Zr 3 (Al, Ag) 2 + Zr 2 (Cu, Ni). The Zr 3 (Al, Ag) 2 phase has a spherical shape with a small size of about 20 nm and is dispersed homogeneously at an interparticle spacing of about 30 nm. The change in the crystallization process by the addition of Ag is presumably due to the generation of the distinction of bonding nature among the constituent elements because of the positive heats of mixing for Ag-Ni and Ag-Cu pairs. The dispersion of the nanoscale Zr 3 (Al, Ag) 2 phase causes a significant increase in tensile fracture strength (σ f ) from 1150MPa for the amorphous single phase to 1520MPa for the amorphous phase containing about 14% volume fraction of Zr 3 (Al, Ag) 2 phase. The shear-type fracture mode along the maximum shear plane remains unchanged. The effectiveness of the Zr 3 (Al, Ag) 2 phase for the increase in σ f is presumably because the size of the phase is too small to contain dislocations. The success of synthesizing the high-strength bulk amorphous alloy consisting of nanoscale Zr 3 (Al, Ag) 2 phase embedded in an amorphous matrix is encouraging for future development of bulk amorphous alloys as a high-strength material.

Mechanisms of brittle fracture of rock with pre-existing cracks in compression

Fracture of rocks containing a multitude of pre-existing cracks is considered from both theoretical and experimental points of view, paying attention mainly to the underlying mechanisms. The competition between a number of mechanisms in producing tear or shear type fractures is discussed in relation to the properties of the rock and the system of pre-existing cracks on the one hand and the type of loading on the other hand. First, 2-D theoretical models and experimental results aimed at the explanation and description of brittle fracture under compression are considered. Their insufficiency and the necessity to address the 3-D peculiarities of crack growth in rock are shown on the basis of new experimental results on 3-D crack propagation in transparent rock-like brittle materials under uniaxial compression. The results show that in contrast to the 2-D case, a single 3-D crack cannot propagate any appreciable distance and the loading results in dynamic, burst-like failure of the sample. Possible mechanisms of the routinely observed extensive fracture propagation in rock samples (splitting), as well as the possibility of shear (oblique) fracture in uniaxial compression, are discussed in connection with these experiments.

Radial Head Fracture

A prospective study was undertaken on 50 acute, consecutive fractures of the radial head. Clinical examination and stress testing were performed on each patient. A valgus stress radiograph, in conjunction with clinical stress testing, was used to assess competence of the medial elbow ligaments. Axial stability of the radius was determined by the axial stress test. Eleven patients (22%) sustained a comminuted radial head fracture; all had instability either to valgus or axial stress. Seventeen patients (34%) had a displaced vertical shear type fracture or an impacted fracture of the radial neck. All sustained some injury to the medial collateral ligament, with variable degrees of valgus elbow instability. Twenty-two (44%) of the fractures were minimally or nondisplaced. All 22 were stable. Radial head fracture morphology can be used to assess the likelihood of associated soft-tissue injury.

Fracture Criterion of a Mixed-Mode Crack. 2nd Report, Mode II Fracture Criterion and Criterion for Judging Fracture Mode.

In the first report, it was shown that, as far as the mode I (opening type) fracture occurs, the criterion ( eI criterion) based on the mode I contribution of Eψ (crack energy density in an arbitrary direction) is effective from completely elastic fracture to elastic-plastic fracture with large yielding region through the application of eI criterion to the fractures of an inclined crack under tensile type loading. However, the mode II (shear type) fracture may occur under some conditions. So, in this paper, the criterion (eIIψmax criterion) based on the mode II contribution of eψ is proposed as the criterion for the mode II fractψre first. Subsequently, the fracture experiments of an inclined crack under shear type loading are carried out and, based on the experimental results, its applicability to mode II fractures is shown in addition to the applicability of eI criterion to mode I fractures and, moreover, the criterion for judging fracture mode is discussed. Finally, by summarizing the results in this paper and those in the first report, the most generalized mixed-mode fracture criterion which can also judge fracture mode is given.

Elastic-plastic fracture behavior of an aluminum alloy under mixed mode loading

M ixed mode elastic-plastic fracture tests were carried out by using A5083-O aluminum alloy compacttension-shear specimens, in which the angle between the loading axis and the crack surface was varied from 90° (mode I) to 0° (mode II) by employing a special loading device. A fractographic investigation was made at various stages of crack tip blunting and stable crack growth. Under mixed mode loadings, opposite deformations appeared at the crack tip: sharpening and blunting. With increasing mode II component, cracks due to shear type fracture initiated at the sharpened corner of the crack tip near the surfaces of the specimen, and then another crack due to dimple type fracture occurred at the blunted corner of the crack tip near the midthickness of the specimen. These experimental results were explained qualitatively by taking account of the stress and strain singularities and triaxial stress distributions near the surface and midthickness of the specimen. Fracture mechanics parameters appropriate for mixed mode elastic-plastic fractures were also studied based on the experimental data.

Simplified sublaminate analysis of composites and applications

An accurate estimate of interlaminar stresses is crucial to understanding as well as predicting many delamination related damages in composite materials. Simplified analytical models … the ply-by-ply bending, the sublaminate bending, and the sublaminate membrane models with decreasing level of complexity are developed to obtain these stresses. These models are based on a bending theory developed earlier. This theory incorporates all the essential physical effects and appears to be an adequate model for predicting the behavior of individual layers in equilibrium. In order to assess the accuracy of these models, three problems are solved: the stress induced in the free edge region of a (0, 90) s laminate in uniform extension, the stress analysis of a compression specimen with end tabs, and the analysis and design of a doublecrack-lap shear type fracture specimen. The results of the free-edge problem are in excellent agreement with the existing numerical solutions, analyses of previously tested compression specimens provide a plausible explanation of observed behavior, and the double-lap fracture specimen behaves as designed. The proposed models are suitable to parametric design-related studies, and according to the need a specific model can be more appropriate.

The plastic deformation and fracture behaviours of α-β brass two-phase bicrystals

The plastic deformation and the fracture mechanism of α-β two-phase bicrystals consisting of an f.c.c. single crystal and a b.c.c. single crystal were investigated by the observations of slip traces, lattice rotations and fracture surfaces. Symmetric, asymmetric and pseudo-identical bicrystals were tested. The slip lines in the β phase near the interface for the symmetric bicrystal were straight until the fracture occurred, while those for the asymmetric and pseudo-identical bicrystals were curved. Such curved slip lines near interfaces were produced by the plastic compatability condition at the interface. The elongations and flow stresses showed the values characterized by the degree of deformation resistance. The two-phase bicrystals showed a shear-type fracture. The fracture in the β phase showed a dimple pattern, while the fracture in the α phase showed a ripple pattern.

Shear fracture of prestressing plain carbon steel wires under complex loading

The usual fracture of prestressing steel wires is of the cup and cone type. However, some authors [1,2] have mentioned a shear type fracture which now and then occurs with an important lowering of the fracture load. We were able to reproduce this type of rupture in the laboratory using two different tests (Fig. I). In the first one the wire is loaded in tension while mandrels produce a local deviation of angle 0. In the second one the wire is loaded in tension while mandrels produce a local compression of magnitude T.

Frature and yield of isotropic elastic material

The frature and yield of an isotropic elastic material are discussed theoretically. The frame-indifferent relation between stress- and strain increments is obtained and it is defined that the fracture and yield may occur when there is no one-to-one correspondence between them. The shear-type fracture and yield conditions are discussed shortly for pressure-insensitive case.

Large Deformation of Notched Perfectly Plastic Tensile Bars

Solutions are obtained for the large, nonsteady deformation of U-notched rigid/perfectly plastic tensile bars in the plane and axisymmetric deformation modes. The solution for the plane mode is shown to be unique. The solutions for both modes are obtained by a general finite-difference method whose accuracy is assessed by examining different mesh sizes in both iterative and noniterative schemes. The solutions may be useful for estimating local stresses and strains in ductile fracture tests even though comparison of calculated and observed deformations indicates some discrepancies due to the neglect of hardening in the theory. The theory does successfully predict yield loads as well as the sharpening of blunt notches and the blunting of acute notches which is observed in axisymmetric tests. It also shows that the largest strains in the plane mode occur on the rigid/plastic boundary reaching a maximum at the surface while those in the axisymmetric mode occur at the center of the root plane. The tensile stresses are maximum at the center of the minimum section for both modes. These results suggest an explanation for the initiation of the shear-type fractures and the cup-cone fractures which are commonly observed in the plane and axisymmetric modes, respectively.

原子炉用ステンレスクラッド鋼溶接継手の高温における応力破断に関する研究

Stress rupture tests with 40 ton tester were conducted at 500 and 600°C for large welded specimens of stainless clad steel, Mn-Mo-Ni steel ASTM A 302 B claded with AISI 304 L, which is essential to nuclear applications. The large specimen, 38 mm thick and 40 mm wide, showed much inferior property to usual small welded specimen.The results of test at 600°C under a stress of 12 kg/mm2 are : (1) The rupture time of transverse as-welded specimen was 55 % of base metal. (2) The rupture times of transverse welded specimens decreased through heat treatment after welding at 550, 650 and 870°C × 1.5 hr as low as to 40, 60 and 90 %, respectively, of as welded specimen. (3) Machining the reinforcement flush with the surface of base metal increased the rupture time of 550°C × 1.5 hr heat treated specimen by 1.5 times. (4) Longitudinal welded specimen was approximately equivalent to base metal in rupture time. (5) Transverse specimen manually welded showed about 50% longer rupture time than submerged-arc welded specimen.Macroscopic and microscopic examinations showed that cracking in rupture occurred along bond in the graphitized heat-affected zone of base metal. The initiation of cracking occurred mostly at the intersection between the surface of bond of stainless weld metal and the cladding surface, viz., the line along which concentration of strees and local strain were most extreme. Crack initiation in backing steel ocurred frequently at the toe of carbon steel weld metal. If the bottom of stainless weld metal were made smooth with cladding surface, the rupture time of transverse welded specimen would become identical to base metal.The test results at 500°C, however, showed 45 degrees shear type fracture which is different from that at 600°C in which fracture occurred along bond.

原子炉用ステンレス・クラッド鋼溶接継手の高温における応力破断に関する研究

Stress rupture tests with 40ton tester were conducted at 500 and 600°C for large welded specimens of stainless clad steel, Mn-Mo-Ni steel ASTM A 302 B clad with AISI 304L, which is essential to nuclear applications. The large specimen, 38mm thick and 40mm wide, showed much inferior property to usual small welded specimen.The results of test at 600°C under a stress of 12kg/mm2 are:(1) The rupture time of transverse as-welded specimen was 55% of base metal.(2) The rupture times of transverse welded specimens decreased through heat treatment after welding at 550, 650 and 870°C×1.5hr as low as to 40, 60 and 90%, respectively, of as-welded specimen.(3) Machining the reinforcement flush with the surface of bese metal increased the rupture time of 550°C×1.5hr heat treated specimen by 1.5 times.(4) Longitudinal welded specimen was approximately equivalent to base metal in rupture time.(5) Transverse specimen manually welded showed about 50% longer rupture time than submerged-arc welded specimen.Macroscopic and microscopic examinations showed that cracking in rupture occurred along bond in the graphitized heat-affected zone of base metal. The initiation of cracking occurred mostly at the intersection between the surface of bond of stainless weld metal and the cladding surface, viz., the line along which concentration of stress and local strain were most extreme. Crack initiation in backing steel occurred frequently at the toe of carbon steel weld metal. If the bottom of stainless weld metal were made smooth with cladding surface, the rupture time of transverse welded specimen would become identical to base metal.The test results at 500°C, however, showed 45 degrees shear type fracture which is different from that at 600°C in which fracture occurred along bond.

Deformation and Fracturing of Thick-Walled Steel Cylinders under Explosive Attack

Tests have been conducted on annealed heavy-walled cylinders of low carbon (1020) steel internally loaded by explosive charges. The purpose of these tests was to obtain basic information on the manner and type of fracturing and plastic flow obtained by extremely high pressures acting for short durations. It was observed that all of the cylinders tended to fracture in long fragments in the same basic pattern, but with variations because of wall thickness and manner of loading. Experimental results indicate that the radial cleavage type of fracture is initiated within the cylinder wall and propagated to the surface, while the shear type fracture associated with the inner portion of the cylinder wall appears as an independent energy relieving process. Microstructure analysis of the cylinder fragments shows a definite relationship between the type of fracture and the amount of distortion of the grain boundary. Considerable shock twinning is present in the cylinder fragments, and the grain structure near the inner surface shows severe distortion and flow. Strain measurements indicate that considerable plastic strain occurs during the explosive loading and cleavage fractures were always observed to occur in association with considerable plastic deformation.