Corner Cracks Research Articles

Study on the Dynamic Mechanical Properties of Metamorphic Limestone under Impact Loading

Abstract To study the dynamic damage and fracture of metamorphic limestone under explosive load and the stability of the surrounding rock, the stress-strain curve, fracture morphology, and energy dissipation characteristics of metamorphic limestone in the Dahongshan mining area under different strain rates were studied by the Hopkinson pressure bar (SHPB), stress wave analysis, and fractal theory. The experimental results show that the crushing form and degree are significantly affected by the loading strain rate. There are several typical failure modes. When the strain rate is 17.56 s−1, there is no obvious failure except corner cracks. When the strain rate is between 26.92 s−1 and 56.18 s−1, the failure mode of the specimen is axial splitting failure, and when the strain rate is 67.34 s−1, splitting and shearing failure occur. With the increase of the strain rate, the growth rate of the dynamic compressive strength slows down. Compared with static compressive strength, the strength factor increases from 1.15 to 4.19. Also, the fractal dimension shows a gentle increase. When Df is in the range of 1.82~2.24, there is a sudden change in fragmentation when the strain rate is in the range of 34.70 s−1~56.18 s−1. Energy dissipation density increases logarithmically with the strain rate. The results reveal the dynamic breaking and energy consumption laws of metamorphic limestone under impact loads with different strain rates and could provide some reference value for the safe and efficient construction in the Dahongshan mining area and similar engineering projects.

Environmentally assisted fracture behavior of edge and corner notched spring steel

The components made out of spring steel are usually subjected to different environmental conditions when in service. The hydrogen embrittlement is one such process which is inevitable for spring steel. The embrittlement will make the material brittle and induce cracks at the edges and corners. In the presentation experimental investigation has been focused on the analysis of the behavior of embrittled spring steel with edge and corner cracks, under impact and bending loads. The specimen preparations and experimentations have been carried out according to ASTM standards. The results have revealed that the embrittlement induced side and corner cracks play a vital role in the fracture process of the spring steel. The mechanism of fracture in edge and corner notched samples has been analyzed with the aid of scanning electron microscopy. The microscopic observations have shown that the failure in the edge and corner cracked samples is almost catastrophic, and increase in the rate of crack growth in these embrittled samples is highly influenced by the embrittlement induced cracks.

Mode-I stress intensity factors for cracked R-fluted shells under complex loads

Based on the conservation law and bending theory, a technique to determine complicated stress intensity factors on three-dimensional components is proposed, A series of closed form expressions of stress intensity factor are derived for cracked shells under different loads, such as bending, tension. The method requires the geometric relationship between multiple singular stress fields from the crack section, and the relationship between the stress at different crack tips can be estimated. In the expression of the stress intensity factor K, K is proportional to the stress σ at the crack tip, and we can get the supplementary equation of between different stress fields K according to the ratio of the stress at the crack tip, then use the J-integral method to calculate the stress intensity factors of different stress fields. In order to verify the feasibility of this method, a cracked R-fluted shells model was constructed. Under the action of the bending moment, the corner crack propagation is simulated through the reserved corner crack, and two crack tips with different stress fields are generated during the simulation. The research result indicates that the proposed method is effective for cracked R-fluted shells, and has universal applicability for solving complex stress intensity factors on three-dimensional components.

Assessment of a numerical strategy for fatigue growth and shape evolution of a corner crack from a pin-loaded hole

The study investigates fatigue growth and shape evolution of a corner crack in a pin-loaded hole by means of three-dimensional FE analyses. The constraint factor/plasticity-induced crack closure strategy was tuned to reproduce experimentally measured crack front shapes. The study quantitatively determines the LEFM acceptability regions using elastic–plastic simulations. It also assesses the sensitivity of crack propagation and shape evolution to the stress distribution along the front, to the relationship between J-integral and stress intensity factor, and to changing propagation rates along different directions. The proposed approach produces very accurate results in terms of crack propagation rate and shape evolution.

Causes of Corner Cracks in Hypoperitectic Microalloyed Steel Billets

The cover image illustrates the causes of corner crack in hypoperitectic microalloyed steel billets. The hot ductility, solidification shrinkage, alloy composition, microstructure and segregation behavior of steel are analyzed in detail. In this study, article number 2100035, Yanping Bao and co-workers present a new mechanism for generating corner cracks in a billet.

Study on application range of SIF calculation method for nozzle corner crack in pressure vessel for ASME XI code

Stress intensity factors (SIF) of a nozzle corner crack in a pressure vessel subject to pressure and thermal loadings are evaluated using finite element method (FEM) and compared with the method described in ASME XI appendix G (2013 section XI). The formula in ASME XI appendix G is defined for the crack corner at a specific location of the nozzle/vessel connection which may limit the structural integrity assessment of the pressure vessel under ever changing pressures and temperatures duty loads during heat-up and cool-down phases. Using FE method SIFs at corners of similar cracks assumed at other nozzle locations are then evaluated and compared with SIFs using ASME formula to assess the degree of conservatism.

Two-dimensional weight function of stress intensity factors for corner cracks emanating from a circular hole

The weight function method is adopted to calculate stress intensity factors along the corner crack front rather than at only two end points, which are pre-requisites in evaluating fatigue growth of corner cracks emanating from a circular hole. Two-dimensional weight function is derived for corner cracks emanating from a circular hole, based on reference stress intensity factors modified by Newman (2018) and corresponding accurate stress distribution on virtual crack face formulized by authors (Guo and Guo, 2019). The obtained weight function is validated against numerical results in the literature and finite element calculations and shows high accuracy. For quick fatigue crack growth prediction in engineering structures, explicit formulae are obtained for typical corner crack shapes with wide ranges of aspect ratio 0.2 ≤ a/c ≤ 2, crack depth ratio 0.1 ≤ a/B ≤ 0.95, crack front angular parameter 0.05 ≤ 2ϕ/π ≤ 0.95 and plate thickness to hole radius ratio B/R = 2. The process can be thereby extended to the estimation of stress intensity factors for corner cracks emanating from a circular hole contained in complicated structures under arbitrary stress distribution.

Stress Intensity Factors for Embedded, Surface, and Corner Cracks in Finite-Thickness Plates Subjected to Tensile Loading.

The aim of this study is to obtain the stress intensity factor (SIF) along the crack front of elliptical cracks located in finite-thickness plates subjected to imposed displacement or applied tensile load, for different crack geometries (relative depths and aspect ratios) and crack configurations (embedded, surface, and corner). The SIF was calculated from the J-integral, obtained by the finite element method. The results show how the SIF grows with the increase in the relative crack depth and with the decrease in the aspect ratio, with the corner crack being the most dangerous configuration and the embedded crack the most favorable configuration. By increasing the plate length, the SIF rises when the plate is under imposed displacement and decreases when the plate is subjected to applied tensile load, both cases tending towards the same SIF curve.

Causes of Corner Cracks in Hypoperitectic Microalloyed Steel Billets

Due to the development of continuous casting technology, the incidence of cracks in the continuous casting process has been significantly reduced. However, a few small cracks still appear during the continuous casting of special steel. For instance, cracks often appear at the corner of the billet during the production of hypoperitectic microalloyed steel. Most research on the causes of corner cracks in hypoperitectic microalloyed steel has focused on investigating the hot ductility of steel and not considered the shrinkage characteristics during solidification. Herein, the hot ductility behavior show that cracks are not related to the hot brittleness of steel. The effects of alloy composition on the phase evolution and shrinkage of steel during solidification are focused. Uneven solidification leads to excessive shrinkage of the corners in the billet, and an air gap is generated between the billet and the mold. The return of temperature in the corner of the billet results in the coarseness of the corner grain. Abnormal solidification also results in the severe deformation of the billet, leading to severe wear with the mold, causing Cu to infiltrate into the billet, and further increasing the crack sensitivity of the steel.

Hydrogen-Assisted Fatigue Propagation in Corner Cracks at Holes Located in Plates under Tensile Loading

In this study, hydrogen-assisted fatigue propagation (a kind of corrosion fatigue phenomenon) in corner cracks at holes located in plates under tensile loading was studied, the results compared with those obtained for propagation by fatigue in air. To this end, numerical modeling was carried out for the case studied to evaluate the advance of the crack front based on the Paris equation and the stress intensity factors (SIFs) obtained by Raju and Newman. The results showed that the cracks tended toward a preferential propagation path in their growth, the effect of the presence of the stress concentrator on the preferential fatigue propagation path being more pronounced in the crack growth by fatigue in air than in the crack growth by corrosion fatigue.

ANALYSIS OF THE EFFECT OF SLAB THICKNESS ON CRACK WIDTH IN RIGID PAVEMENT SLABS

Cracks that occur in rigid pavements include longitudinal cracks, transverse cracks, and corner cracks. The relatively large crack width not only spoils the aesthetics of the concrete structural elements but can also lead to structural failure. This study aims to determine the crack width of a rigid pavement concrete slab located above the subgrade which is considered a beam on an elastic foundation, so that a minimum rigid pavement concrete slab thickness can be recommended. The specimen will be observed at various thicknesses to obtain the optimum thickness. The load used is a centralized monotonous load, which represents the load of the truck vehicle. The research limitation is using a test object in the form of a concrete plate measuring 2000x600 mm which is placed on the ground with CBR=6 %. The quality of reinforced concrete slabs is fc'=40 MPa and fy=440.31 MPa. The thickness of the concrete slab varies between 100 mm, 150 mm, and 200 mm. The slab placed on the ground is then given a central loading in the form of a centralized monotonic load. The loading range starts from a load of 2–180 kN with a load interval of 2 kN. The experimental results show that the rigid pavement slab has a bending failure so that the crack pattern that occurs begins with the first crack on the underside of the slab. The crack pattern in terms of slab thickness variation has a similar pattern. The initial crack width on the slab is 0.04 mm. The thicker the slab smaller the crack width at the same load. Based on the maximum allowable crack width=0.3 mm. For loads between (80–100) kN (Road Class I, II, and III), a minimum thickness of rigid pavement slabs (70–80) mm is recommended. For loads between (130–140) kN, the minimum thickness of the rigid pavement slab (105–115) mm is recommended

Research on rolling process of bow parts with variable lateral roll spacing based on optimal bending angle distribution function

For roll-bending formation in bow-shaped sheet metal parts, the distance of the traditional roll-forming transverse unit is constant, which often causes corner wrinkles, corner cracks, tearing, springback, and peak longitudinal strain defects throughout the formation process. To solve these shortcomings, this paper proposes an optimized bending angle distribution function to synergize the variable lateral roll distance technique. By parameterizing the abstract function according to the function boundary trajectory, the bending angle of each roll pass is measured; furthermore, the optimal function curve can be obtained through finite element analysis. Then, the roll-bending simulation is conducted, and the forming angle of the sheet metal parts is redistributed to determine the most effective reduction of peak longitudinal strain and transverse roll spacing. The bending angle distribution function aids the variable transverse roll distance technology to execute roll-bending experiments on 3004Al arch parts, ultimately obtaining the optimal roll-bending angle and transverse roll distance. The results of the roll forming simulation, based on the optimized bending angle distribution function and variable transverse roll distance technology, corroborate the experimental results, and good roll forming efficiency and quality are achieved.

Assessment of Failure along Re-Entrant Corner Cracks in Existing RC Dapped-End Connections

Reinforced concrete dapped-end connections are common in existing bridges and represent a critical component of the structure. Due to high stress concentrations in the re-entrant corner of the connection, dapped-ends typically feature inclined corner cracks that occur under service loads. Widening of these cracks due to material degradation and increasing loads can lead to yielding of the dapped-end reinforcement and subsequent failure of the connection. While most of the research devoted to predicting the peak resistance of such dapped-end connections has focused on the strut-and-tie and stress field modelling approaches, there remains a need for mechanical models that facilitate the direct use of on-site measurable data for assessing the strength of the connection. This paper presents the derivation of such a model based on first principles: kinematics, equilibrium and constitutive relationships. The model utilizes measured angles of the inclined crack as an input, and explicitly accounts for kinematic parameters such as the width and the length of the corner crack. A database of 47 tests from the literature featuring variable properties is used to validate the model. It is shown that the proposed approach captures well the peak resistance of dapped-end connections governed by the widening of the crack at the re-entrant corner, leading to an average strength experimental-to-predicted ratio of 1.10 and a coefficient of variation of 8.6%. Furthermore, the model is used to discuss the effect of the angle of the critical corner crack on the peak resistance of the connection.

A Novel Specimen Produced by Additive Manufacturing for Pure Plane Strain Fatigue Crack Growth Studies

Fatigue crack growth is usually studied using C(T) or M(T) specimens with through-thickness cracks. The objective of the present study is to propose a cylindrical specimen with central crack, produced by additive manufacturing. This geometry allows to have pure plane strain state along the whole crack front, avoiding the complexities associated with corner points, crack shape, and variation of crack closure along crack front. Additionally, this geometry may be used to develop studies in vacuum, avoiding expensive vacuum equipment, since the air is not in contact with the crack front. Cylindrical specimens of Ti6Al4V titanium alloy were produced by Selective Laser Melting and tested at a stress ratio R = 0. Marking with overloads was the solution adopted to measure the length of the internal cracks. The fracture surfaces presented circular crack fronts and the da/dN-ΔK curves showed a great influence of atmosphere on fatigue crack growth. An average difference of 50% was found between the results in air and vacuum. Therefore, this geometry with internal crack is an interesting alternative to through-thickness geometries.

Seismic performance analysis of corrugated-steel-plate composite shear wall based on corner failure

This study investigates the hysteretic performance of corrugated steel plate composite shear walls. Six shear walls were designed for experimental research to analyze the failure process and mode, hysteresis diagrams, backbone curves, energy consumption capacity, and stiffness degradation. The peak loads of SPCSW-1, SPCSW-2, and SPCSW-3 were 688.8 kN, 733.0 kN, and 547.2 kN, respectively, representing increases of 252.8%, 200.4%, and 141.8% (compared with SPSWs: 272.5 kN, 365.7 kN, and 385.8 kN). According to the experimental failure mode, the conventional model was further optimized to achieve corner cracking. The optimization scheme and mechanism analysis of the model were explored. The shear strength formula for a horizontal corrugated steel plate composite shear wall was revised, considering the adverse effect of corner failure, and the shear sharing percentage was determined. The simulation results indicate that the steel type may affect the peak load of the composite shear wall. The energy consumption ratio of the outside concrete, steel plate, and tension column to the pressure column is 13:3:3:1; the ratio is minimally affected by the steel type. The steel skeleton cannot provide full support due to stress concentration after the failure of the concrete corner, which causes adverse conditions. The revised formula was demonstrated to be more accurate for the shear strength calculation of a horizontal corrugated steel plate composite shear wall.

Elastic-plastic solutions for corner and surface cracks emanating from stress concentrators

Three-dimensional (3D) constraint effects for part-through cracks, such as corner and surface cracks, emanating from stress concentrators play important role in damage tolerance design of structures, but have hardly been investigated in the frame of 3D elastic–plastic fracture theory. Here the ability of current elastic–plastic solutions to describe 3D constraints and their effects on crack tip fields of corner and surface cracks emanating from stress concentrators are systematically analyzed using finite element (FE) method. Distribution of the out-of-plane constraint factor Tz and corresponding in-plane constraint parameters QT and AT can quantify the effect of stress concentration on crack tip fields. Good agreement between 3D elastic–plastic solutions (J-Tz, J-Tz-QT, J-Tz-AT) and FE results is obtained for four typical specimens at relatively high and low loading levels, showing that these solutions can serve as the theory foundation for advanced damage tolerant analyses of engineering structures.

Research on the Fatigue of Small Impulse Turbine Blade Based on the Numerical Simulation and Experimental Tests

Reusable spacecraft is increasingly attracting researchers’ attention. However, the experimental investigations on the turbine blade of the rocket engine are rarely published. Thus, the fatigue of a small impulse rocket turbine blade is explored in the current work. First, the specimen and the electrode of electrical discharge machining are carefully designed. Then, the electrical discharge machining is used to machine the specimen. To study the fatigue properties, the finite element analyses are separately performed on the blade model and the specimen. Based on the numerical results, a fatigue test is carried out to reproduce the most vulnerable position. Finally, the microstructural structures of the specimen are detected using the scanning electron microscope (SEM). Results show that (1) different from the aviation field, the specimen is unable to be machined with the welding method because it destroys the crucial details and the mechanical properties; (2) the maximum plastic strain is present at the leading edge close to the hub, at which a 760 μm corner crack appears at the 10113th fatigue cycle. This work provides a feasible method of using the EDM process to machine specimen for the small impulse turbine blade.

Formation and Control of Transverse Corner Cracks in the Continuous Casting Slab of a Microalloyed Steel

To investigate transverse corner cracks for a microalloyed steel continuous casting slab, the metallography, microtopography, and three‐dimensional (3D) morphology of cracks are studied, respectively. High‐temperature mechanical properties are investigated and compared from two positions where samples are extracted from both the slab corner and surface of the slab center. The thermal history of the slab is simulated and optimized experiments are conducted. Transverse corner cracks are generated on the valley of oscillation marks. Mold powder and wear elements of the mold are not detected. Microstructures are refined near the cracks. Cracks are generated in secondary cooling zones and the cracking temperature is higher than Ar3 temperature. The extension path of cracks is not linear and cracks extend along the grain boundary. The third brittle temperature ranges (TBTR) are 764–832 °C and 793–808 °C in the two positions, respectively. The temperature at the slab corner in the bending and straightening zone falls into the brittle zone during the original water cooling condition, leading to the formation of cracks. The secondary cooling scheme is optimized to prevent the temperature at the slab corner in the bending and straightening zone from entering the TBTR, significantly reducing the occurrence of transverse corner cracks.

Influence of edge and corner cracks on the impact and bending behavior of spring steel

During the course of production of the spring steels, depending on the production process, the ductility drop and decrease in strength will lead to crack formation in the spring steel. Also some of the strength enhancing heat treatment process directly influences the service performance of spring steel by the emanating edge and corner cracks, which is an important scientific issue. The present experimental investigation focuses of the impact and bending behavior of spring steel with varied edge and corner crack configurations. The behavior of the material has also been investigated to ascertain its satisfactory service temperature. The specimen preparation and the experimentations have been carried out according to the ASTM standards. The results have revealed that the corner cracked spring steel can give effective service till 100 °C, beyond which it will decrease drastically. It is also determined that the double corner cracked samples have highest impact energy and lowest is noted for triple corner notched samples. In case bending loads the, the double edge notched sample loaded in the thickness direction has shown maximum strength and the lowest in noted for the triple sided notched samples. Finally it can be stated that the presence of edge and corner cracks in the spring steel will reduce the strength, service life and will lead to the most dangerous catastrophic failure.

Application of J2 Integral Method in Calculating Complicated Stress Intensity Factors on Three-dimensional Components

In this paper, a technique to determine complicated stress intensity factors on three-dimensional components, which based on the conservation law and the elementary mechanics is proposed, it only needs the geometric relationship between multiple singular stress fields from the crack section, and obtaind the relationship between the stress at different crack tips. In the expression of the stress intensity factor K, K is proportional to the stress σ at the crack tip, and we can get the supplementary equation of between different stress fields K according to the ratio of the stress at the crack tip, then use the J-integral method to calculate the stress intensity factors of different stress fields. In order to verify the feasibility of this method, a cracked R-fluted shells model was constructed. Under the action of the bending moment, the corner crack propagation is simulated through the reserved corner crack, and two crack tips with different stress fields are generated during the simulation. The experimental result indicates that the proposed method is effective for cracked R-fluted shells. It is also shown that the method has universal applicability for solving complex stress intensity factors on three-dimensional components.