Cracking Of Steel Research Articles

Experimental study on recovery stress behavior of memory-steel patches bonded on cracked steel plates

The use of iron-based shape memory alloy (Fe-SMA) demonstrates effectiveness in repairing cracked steel structures for lifetime extension. This study presents an activation test of memory-steel (i.e., Fe-SMA) patches adhesively bonded on cracked steel plates to investigate the recovery stress behavior. Fe-SMA strips with different lengths ranging from 100 to 500 mm are bonded over cracks using a ductile nonlinear adhesive. The middle part of the Fe-SMA strip (over the crack) is activated using the electrical resistive heating technique. The Fe-SMA is heated to a target temperature of 180 ℃ and subsequently cools down to the room temperature. The temperatures of the anchorage parts are maintained below the adhesive glass transition temperature during the activation process. After activation, final Fe-SMA prestresses ranging from approximately 154 to 249 MPa are successfully generated and sustained across all the specimens, resulting in average compressive strains of approximately -40 to -120 µm/m in the steel plates.

Study of corrosion-resistant steels in hydrogen sulfide-containing environments of oil and gas fields

Hydrogen sulfide corrosion cracking of steel occurs in deposits containing corrosive components - hydrogen sulfide and carbon dioxide (carbon dioxide). The mechanism of corrosion cracking of steel in hydrogen sulfide-containing environments of corrosive oil and gas fields is considered, and factors influencing hydrogen sulfide cracking are identified. Increasing the performance properties of carbon, low-alloy, structural steels resistant to hydrogen sulfide and sulfide cracking was carried out on the basis of improving the composition of the components of chemical elements and the structural state through the choice of heat treatment methods depending on the acidity and temperature of the environment, partial pressures of carbon dioxide and hydrogen sulfide. Laboratory and production tests have shown the durability of the proposed compositions chemical elements of steels to hydrogen sulfide cracking, sulfide cracking and hydrogen swelling in deposits containing corrosive components was 70–80% compared to existing carbon structural steels.

An Attention-Based Detection Method of Displacement Field on Steel Surfaces

Steel structures are prone to fatigue cracks when subjected to cyclic loading, which may lead to catastrophic failure. Generally, the width of fatigue cracks in steel structures is below 0.1 mm at the early stage of crack propagation. Although high-resolution images can be obtained by consumer-grade cameras at low cost, these tiny cracks are difficult to detect by images alone. This paper proposed a crack detection method based on the displacement field on the surface of the structure obtained from images. Video or continuous images of the target structure under loading was first taken and input into an improved Detector-Free Local Feature Matching with Transformers (LoFTR) model, which was capable of densely matching feature points on two pairs of images without distinct visual features. The surface displacement field of the structure was then performed inversely by the coordinate difference of a large number of matched feature points. Eventually, location of the crack was extracted according to discontinuities in the displacement field. A case study was conducted on a cracked steel plate. Results demonstrated a tiny crack with the maximum width of 0.1 mm was detected, which was more effective and accurate in comparison with image-based semantic segmentation methods.

Modeling fatigue-assisted pitting in pipeline steel with PCA-XFEM

We present a localized corrosion and cracking damage mechanism (initiation of the pit, propagation of the pit, pit-to-crack transition, and stable cracking) in a pipeline steel under the application of fatigue loading by using sequential coupling of Probabilistic Cellular Automata (PCA) and eXtended Finite Element Method (XFEM). PCA is utilized for describing the localized corrosion damage mechanism. XFEM is used to simulate arbitrary inhomogeneities (cracks, voids, and soft/hard material interfaces (inclusions)) with the help of Level Set Methods (LSM). In the XFEM, the standard finite element is enriched by additional degrees of freedom by invoking the notion of the partition of unity, which alleviates the burden of mesh conformity to the internal boundaries and avoids re-meshing. LSM is used to locate the voids and material interfaces and track the crack propagation location. A localized strain criterion initiates cracks from the pit surface when the pit reaches a critical strain value.The coupling of PCA and XFEM demonstrates good agreement with experimental data regarding stress-assisted pitting corrosion and pit-induced fatigue cracking in the pipeline steel. The study also investigates the effects of boundaries, and initial pit size on fatigue crack initiation and growth. Boundary effects significantly influence crack initiation life and growth behavior, highlighting the importance of considering both defect characteristics and boundary conditions in assessing fatigue performance and structural integrity. Various initial pit sizes and geometric features further affect crack initiation location and transition time. Furthermore, the PCA-XFEM model effectively captures crack behavior in both short and long crack regimes, demonstrating good agreement with experimental data for a selected pit width of 140μm. By incorporating crack driving parameters derived from experiments, the model accurately predicts crack propagation, further enhancing its reliability and predictive capabilities in assessing fatigue crack behavior. Overall, this approach provides valuable insights for predicting the service life and integrity of pipelines subjected to similar loading conditions, thus aiding in designing and maintaining these critical infrastructure components.

Microstructural Characterization of Hot Shortness in Steels

Hot shortness in steels is a macro crack on the steel surface especially on the slab edges of hot rolled steels produced by recycling. Hot shortness in steels is characterized by intergranular cracking of steel on the surface during hot rolling process. The hot shortness damage can be seen by naked eye due to macro cracks on steel surface, after the hot rolling of slab. Although macro cracks can occur due to various parameters such as excessive force or deformed rolls, hot shortness is directly linked to residual elements in the steel composition. Most common and effective residual element for hot shortness is copper. Copper in steel originates from the used scrap in Electric Arc Furnace (EAF) steelmaking. Decreased primary sources and environmental concerns with increased scrap output in the world make the recycling of steel inevitable. Copper segregates in the austenite grain boundaries during the annealing of steel prior to hot rolling. Liquified copper film decreases the grain cohesion between austenite grains and results in intergranular cracking by the force applied during the rolling. Detection of copper in microstructure is vital to understand mechanism of hot shortness. Common knowledge in the literature of hot shortness suggests that hot shortness mechanism consists of oxidation-segregation-decreased grain cohesion-crack route. In this study, detailed microstructure images of steel surfaces are discussed with optical and scanning electron microscopy examinations. Examined samples of hot shortness are collected from scientific experiments and industrial practice examples. Helpful techniques and etching agents for copper revelation in microstructure are evaluated and explained in this paper.

Estimation of stress concentration factor at stop-hole repair strengthened by bonded patches

Fatigue cracks detected in existing steel structures during periodic inspections are often tentatively repaired by drilling holes, called stop-holes, at crack tips. However, in some cases, fatigue cracks may reoccur at the edge of stop-holes, depending on the crack length and applied stress range. Although numerous studies have demonstrated the efficacy of patch plates in strengthening cracked steel plates and extending fatigue life of steel structures, there is a limited literature on the effectiveness of stop-hole repair strengthened by bonded patches. Particularly, the impact of the bonded patch configuration and position on the fatigue strength improvement remains unexplored. This study investigated the influence of the bonded patch configuration and position on the stress concentration factor of a stop-hole by finite element analysis. In this study, the material of bonded patch plates is assumed to be steel. Furthermore, this study presents a fatigue design equation for stop-hole repair strengthened by bonded patches, considering bonded patch configuration and position based on the fracture mechanics. The proposed design equation enables the design of patch configuration and the evaluation of remaining fatigue life to repair fatigue cracks in existing structures.

Stress Corrosion Cracking of Austenitic Stainless Steels in Environments Relevant to Spent Nuclear Fuel Storage

Localized corrosion and stress corrosion cracking (SCC) are potential degradation mechanisms for stainless steels (SS) during exposure to corrosive environments. When localized corrosion features are subject to stresses (either external or residual), a crack can nucleate and grow. One potential scenario under which chloride-induced SCC may pose a risk is the interim storage of spent nuclear fuels (SNF) in SS canisters. In the U.S., these SS canisters are located at interim spent fuel storage installations across the country. As canisters cool over time, dust deposition can lead to the formation of corrosive brines, which form by various salt compositions. Initial studies have shown significant influences of environment on corrosion severity and morphology, which may in turn influence crack nucleation and growth. Recent, compositional analysis of salts on the surface of interim SNF SS storage canisters has been carried out with representative brine mixing formulations developed for laboratory exposures. This presentation evaluates the corrosivity, specifically in-situ crack growth rates influenced by the electrochemical environment of the prepared brines as compared to saturated salts and other seawater surrogate brines. The crack growth rates, in-situ electrochemical measurements, as well as fractography will be discussed in terms of testing methodologies and potential risks for canister degradation. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This document is SAND2023-02249A.

Fatigue performance and parameter optimization of CFRP-reinforced steel plate considering elevated temperature

This article aims to investigate the effect of elevated temperature on the fatigue performance of CFRP-reinforced cracked steel plates and optimize the design parameters for their reinforcement. Based on the self-developed adhesive GY34, a finite element model of the CFRP-reinforced central cracked steel plate is established by the ABAQUS software. Parametric analysis is carried out on different bonding methods of CFRP plates and different thicknesses of adhesive layers for CFRP-reinforced cracked steel plates. The effect of elevated temperature on the reinforcement is also studied to verify the excellent performance of GY34 adhesive. Furthermore, the enhancement of fatigue life for cracked steel plates reinforced with CFRP plates at different temperatures is investigated using the Paris model and modified Newman model. The results show that double-sided reinforcement with CFRP is more effective than single-sided reinforcement. All of the different bonding methods could reduce effectively the stress intensity factor of cracked steel plates and improve significantly the bearing capacity of the steel plates. Among them, increasing the number of CFRP layers and their elastic modulus yield the most significant improvement on the reinforcing effect. Elevated temperatures effect greatly on the mechanical properties of adhesively bonded CFRP-reinforced steel plates. The effective bonding length and the stress intensity factor amplitude at the crack tip of the steel plate increases with temperature rises, which may accelerate the growth rate of fatigue crack and reduce the reinforcing effect on fatigue life.

Effects of Mode Mixity and Loading Rate on Fracture Behavior of Cracked Thin-Walled 304L Stainless Steel Sheets with Large Non-Linear Plastic Deformation.

This study investigates the mixed-mode I/II fracture behavior of O-notched diagonally loaded square plate (DLSP) samples containing an edge crack within the O-notch. This investigation aims to explore the combined effects of loading rate and mode mixity on the fracture properties of steel 304L, utilizing DLSP samples. The DLSP samples, made from strain-hardening steel 304L, were tested at three different loading rates: 1, 50, and 400 mm/min, covering five mode mixities from pure mode I to pure mode II. Additionally, tensile tests were performed on dumbbell-shaped specimens at the same loading rates to examine their influence on the material's mechanical properties. The findings revealed that stress and strain diagrams derived from the dumbbell-shaped samples were largely independent of the tested loading rates (i.e., 1-400 mm/min). Furthermore, experimental results from DLSP samples showed no significant impact of the loading rates on the maximum load values, but did indicate an increase in the ultimate displacement. In contrast to the loading rate, mode mixity exhibited a notable effect on the fracture behavior of DLSP samples. Ultimately, it was observed that the loading rate had an insignificant effect on the fracture path or trajectory of the tested DLSP samples.

In-Depth Steel Crack Analysis Using Photoacoustic Imaging (PAI) with Machine Learning-Based Image Processing Techniques and Evaluating PAI-Based Internal Steel Crack Feasibility

Steel plays an indispensable role in our daily lives, permeating various products ranging from essential commodities and recreational gears to information technology devices and general household items. The meticulous evaluation of steel defects holds paramount importance to ensure the secure and dependable operation of the end products. Photoacoustic imaging (PAI) emerges as a promising modality for structural inspection in the realm of health monitoring applications. This study incorporates PAI experimentation to generate an image dataset and employs machine learning techniques to estimate the length and width of surface cracks. Furthermore, the research delves into the feasibility assessment of employing PAI to investigate internal cracks within a steel sample through a numerical simulation-based study. The study’s findings underscore the efficacy of the PAI in achieving precise surface crack detection, with an acceptable root mean square error (RMSE) of 0.63 ± 0.03. The simulation results undergo statistical analysis techniques, including the analysis of variance (ANOVA) test, to discern disparities between pristine samples and those featuring internal cracks at different locations. The results discern statistically significant distinctions in the simulated acoustic responses for samples with internal cracks of varying sizes at identical/different locations (p < 0.001). These results validate the capability of the proposed technique to differentiate between internal crack sizes and positions, establishing it as a viable method for internal crack detection in steel.

Effect of pre-strain on critical conditions for hydrogen-induced delayed cracking and crack nucleation characteristic of DP1180 steel

Hydrogen-induced delayed cracking represents a significant threat to the dependable performance of advanced high-strength steel. This study employed constant load tensile tests to uncover critical conditions for hydrogen-induced delayed cracking of DP1180 steel plate, establishing a precise relationship between pre-strain, threshold stress, and critical hydrogen concentration. Furthermore, this research explored dislocation slip transfer at grain boundaries, utilizing geometric compatibility factor (m') and residual Burgers vector (br), and analyzed slip characteristics at martensite/martensite, ferrite/ferrite, and martensite/ferrite interfaces. These findings provide valuable references for the safety assessment of DP1180 in hydrogen-exposed environments.

Analysis of the Effect of Yield Stress on Stress Corrosion Cracking of Martensitic and Ferritic Steels in Acidic Environments

Analysis of the Effect of Yield Stress on Stress Corrosion Cracking of Martensitic and Ferritic Steels in Acidic Environments

Water quenching cracking mechanism and prevention of steels

ABSTRACTQuenching is often an essential step in heat treatment of steels for enhancing strength. Water quenching which is low cost and free of pollution risk instead of oil quenching or polymer aqueous solution quenching which is high cost and has high pollution risk will be widely used in heat treatment enterprises. However, the problem of easy cracking of low alloy steels (especially medium carbon low alloy steels) quenched in water has long been a concern for many researchers. The finite element simulation (FES) is used to predict transient stress at cracking position during quenching of an AISI 4140 steel cylinder sample and found that the transient tangential tensile stress at cracking position was only 350 MPa which is smaller than half of the yield strength (775 MPa) of AISI 4140 steel. Such a low tensile stress causing quenching cracking is surprising. To ascertain the underline reasons, a phase-field finite element (PFFE) model is established to investigate the microscopic stress distribution produced by martensitic transformation. The results indicate that the microscopic stress at the junction of the lath martensitic variants in AISI 4140 steel exceeded 800 MPa, and thus such a high microscopic stress is considered as the origin of quenching cracking. By using two examples, our work further clarifies the basic principle of the water–air alternative timed quenching (ATQ) process invented by us as a process suitable for engineering applications with the ability to avoid water quenching cracking and ensure mechanical properties.

Seismic Analysis Model of Partially Concrete-Filled Steel Piers Considering Ultralow-Cycle Fatigue Crack Propagation

ABSTRACT Seismic performance of partially concrete-filled steel tube (PCFST) bridge piers is controlled by the coupled failure of ultralow-cycle fatigue (ULCF) and local instability of steel plates. An empirical formula was established for the plastic fracture displacement on average stress triaxiality of the crack intiation process, and the two-stage prediction model for the ULCF cracking of steel was improved. Furthermore, an empirical formula was established for the plastic strain amplification factor on the element size and the stress triaxiality of the coarse model. A complete modeling method was proposed for the seismic performance analysis model of PCFST piers considering ULCF cracking.

Revealing the cleavage mechanism of the crack propagation process in martensitic steels

A phase field model is presented to investigate the influence of cleavage planes in martensite and austenite phases and the loading rate on the crack propagation process with considering the Kurdjumov-Sachs (K-S) orientation relationship in martensitic steels by the finite element method. The transgranular (through the martensite and austenite phases) and intergranular (along the martensite/austenite interface) fracture processes in martensitic steels can be simulated by this model. This model can simulate the crack propagation in martensitic steels with displaying the crack propagation path in austenite and martensite phases and stress distribution directly. Moreover, this model reveals the energy difference required by transgranular and intergranular fracture in martensitic steels and the hindering effect of martensite on the crack propagation process. The simulation results further indicate that the preferential cleavage planes of crack propagation in martensite and austenite phases are (100)α’ and (111)γ planes, respectively, which is consistent with the experimental results in martensitic steels. An interesting finding is that the influence of the loading rate on the maximum loading for material failure only acts on the crack propagation stage rather than the crack initiation stage. Therefore, this model can be a powerful tool to investigate the cleavage mechanism of the crack propagation process during the water quenching process and to avoid water quenching cracking in martensitic steels.

Liquid Metal Embrittlement Cracking in Uncoated Transformation-Induced Plasticity Steel during Consecutive Resistance Spot Welding

In the automotive production line, a single pair of electrodes is employed to produce hundreds of consecutive welds before undergoing dressing or replacement. In consecutive resistance spot welding (RSW) involving Zn-coated steels, the electrodes undergo metallurgical degradation, characterized by Cu-Zn alloying, which impacts the susceptibility to liquid metal embrittlement (LME) cracking. In the present investigation, the possibility of LME crack formation in uncoated TRIP steel joints during consecutive RSW (involving 400 welds in galvannealed and uncoated TRIP steels) was investigated. The results have shown that different Cu-Zn phases were formed on the electrode surface because of its contamination with Zn from the galvannealed coating. Therefore, during the welding of the uncoated TRIP steel, the heat generated at the electrode/sheet interface would result in the melting of the Cu-Zn phases, thereby exposing the uncoated steel surface to molten Zn and Cu, leading to LME cracking. The cracks exhibited a maximum length of approximately 30 µm at Location A (weld center) and 50 µm at Location B (shoulder of the weld). The occurrence and characteristics of the cracks differed depending on the location as the number of welds increased due to the variation in Zn content. Type A cracks did not form when the number of welds was less than 280. Several cracks with a total length of approximately 30 μm were suddenly formed between 280 and 400 welds. On the other hand, type B cracks began to appear after 40 welds. However, the number and size of these exhibited inconsistency as the number of welds increased. Overall, the results have shown that small LME cracks can form even in uncoated steels during consecutive welding of Zn-coated and uncoated steel joints.

Rigorous SIF-based prediction of fatigue life improvement for prestressed-CFRP-repaired cracked steel plates

Carbon fiber reinforced polymer (CFRP) can be widely used to repair damaged plates in marine engineering equipment. To predict the fatigue life improvement by this repair, the stress intensity factor (SIF) of the cracked plate without/with repair is analyzed rigorously. Specifically, the SIF of a cracked plate without repair is analyzed and the error due to the finite element model (FEM) mesh is evaluated by comparing with the exact solution. By applying the same mesh having the same error, the exact SIF of the repaired plate is obtained in a convenient form. Fatigue experiments reveal that the same crack propagation parameters (C and m) can be applied for the unrepaired/repaired plates. Based on those, the prediction equation of fatigue life is obtained for cracked steel plates repaired with prestressed CFRP. The results show that this prediction method has the advantages of simplicity and efficiency.

Repairing Behaviors of Cracked Steel Plates Based on Bolted Fiber-Reinforced Polymer Plates.

The use of FRP materials to repair cracked/damaged steel structures has gradually been adopted by researchers. This paper investigates the repairing effect of bolted FRP plates for cracked steel plates based on experimental and numerical simulation methods. In the experimental investigation, the tensile strengths of six specimens, including three repaired specimens and three pure cracked steel specimens, were evaluated. The test outcomes indicated that the bolt repairing method significantly enhanced the tensile strengths of the cracked steel plates. As an example, the failure of a pure steel plate with a 1 mm width crack occurred at 813 N, whereas after being repaired, a tensile strength of 1298 N was observed. Based on finite element (FE) analysis, the influence of bolt preloads and interfacial friction coefficients were verified. The stress-relative ratio for specimens was contingent on the bolt preload magnitude and gradually decreased as the preload was augmented. By exploring the repairing effect for varied friction coefficients, it was concluded that using a higher bolt preload can aid in eliminating the performance discrepancy of the overall component caused by interface treatment errors.

Evaluation of the impact of chloride ion concentration on stress corrosion cracking in E690 steel under low pH conditions

In this work, the effect of Cl- concentration on the stress corrosion cracking (SCC) behavior of E690 steel in low pH solution was studied. The SCC behavior of E690 steel is controlled by the combination of anodic dissolution and hydrogen embrittlement. The Cl- concentration has a significant effect on the electrochemical reaction, and icorr and Ecorr increase first and then decrease as the Cl- concentration increases from 0.5 to 4.0 mol/L. The SCC behavior of E690 steel is affected by the electrochemical reaction. Thus, the SCC susceptibility increases first and then decreases as the Cl- concentration increases from 0.5 to 4.0 mol/L.

Experimental observations of nucleation and crack growth paths of hydrogen-induced cracking in pipeline steel

The microstructural features that favor hydrogen-induced cracking (HIC) in internal, middle, and external layers of pipeline steels were investigated. The electrochemical cathodic charging was used to induce HIC, and straight beam ultrasonic inspection was identified in which steel layers HIC nucleate and grow. The cracked plates were examined by optical microscope and scanning electron microscope (SEM). The hydrogen microprint technique (HMT) was used to visualize the site of high hydrogen concentrations. Electron backscatter diffraction (EBSD) was used to analyze the role of crystallographic texture in HIC pathways. The results revealed that HIC nucleation and growth are influenced by the segregation degree and inclusion contents, which are higher in the internal surface layer of our studied steels but not consistently so in the middle thickness layer. Further, HIC nucleated in cuboidal and spinal inclusions and propagated along ferrite/pearlite bands with high misorientations. The HMT results showed that hydrogen is present in pearlite colonies, grain boundaries, and non-metallic inclusions. The results indicated that HIC is not solely controlled by the crack geometry.