Cracked Steel Plates Research Articles

Experimental study on the fatigue behavior of CFRP-strengthened cracked steel plates under eccentric axial tension

In this paper, an experimental investigation has been conducted to study the fatigue behavior of single edge-notch steel plates strengthened with CFRP (laminates/sheets). The plates have been subjected to eccentric fatigue under axial loading conditions. The experimental study includes fourteen specimens and has been tested under axial loading until failure. The constant parameters in the study are steel material grade, steel plate dimensions, and fatigue loading conditions. Meanwhile, the studied parameters are steel plate initial edge crack size, CFRP configurations (length, one or two-sided, and laminates or sheets), and adhesive material strength. The experimental results revealed that the fatigue life for specimens strengthened with CFRP sheets or CFRP laminates can be improved by a factor of 1.15 to 3.87 and 1.47 to 6.32, respectively, compared with the un-strengthened specimens. The results show that using CFRP can be considered an efficient way to repair the initial cracks in steel elements under eccentric axial fatigue loading.

Investigation of Stress Intensity Factor Reduction using Steel and GFRP Patches for Repairing Edge Cracks in Steel Plates

The ultimate objective of this study was to compare the performance of repaired edge cracks in steel plates before and after repair with patches made of steel patch and glass fiber-reinforced polymer composite patches (GFRP) in different shapes: circular, rectangular, and trapezoidal, under two conditions: unsymmetric patch (one patch) and symmetric patch (two patches). A three-dimensional finite element model of the one-sided and two-sided repaired examples is used to study how the steel and composite patch affect the stress intensity factor (SIF). Under uniaxial tensile loads, the use of steel patches and GFRP composite patches to repair cracks was studied. The results showed that the steel patch performs better than the GFRP patch because it significantly lowers the stress intensity factor (SIF). The symmetric patch arrangement (two patches) is better than the un-symmetric patch arrangement (one patch) because it significantly reduces the stress intensity factor (SIF).

Fatigue performance of carbon fiber‐reinforced polymer strengthened single‐edge cracked steel plates: Effects of adhesive property and CFRP arrangement

AbstractCarbon fiber‐reinforced polymer (CFRP) is increasingly used to improve the fatigue behavior of damaged steel structures due to its advantages, including high strength and convenient processing. However, several issues, such as the effects of the adhesive property and CFRP arrangement, still need to be studied. In this study, a total of 20 single‐cracked steel specimens were tested under fatigue load, including two unstrengthened specimens, six single‐sided strengthened specimens, and 12 double‐sided strengthened specimens. The failure mode, fatigue life, crack propagation pattern, and interface damage development were obtained from experiments. The results show that epoxy resin structural adhesives (adhesives Araldite 420 and J133C) have the best bonding properties with CFRP. For the conventional epoxy adhesives, Araldite 420 and J133C can considerably improve fatigue life, which increased by more than 44.84 times to unstrengthened specimens. CFRP plate strengthening can significantly improve the fatigue life of single‐edge cracked steel plates. For the double‐sided strengthened specimens, the fatigue life can be improved by 6.93–44.84 times that of unstrengthened specimens. For the single‐sided, the fatigue life can be improved by 2.24–2.77 times. Properties of epoxy adhesive have a more significant effect on fatigue life compared to the thickness of the CFRP plate due to debonding.Highlights Ductile epoxy adhesives are most conducive to improving the fatigue behavior of CFRP strengthened steel plates. The fatigue life of steel plates can be improved by increasing the thickness of CFRP plates and using double‐sided CFRP strengthening. Interface debonding is the main failure mode of CFRP plates strengthening single‐edge cracked steel plates under fatigue.

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.

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.

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.

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.

Strengthening Cracked Steel Plates with Shape Memory Alloy Patches: Numerical and Experimental Investigations

To investigate the retarding effect of bonding the shape memory alloy (SMA) patches on crack propagation in steel plates, both numerical and experimental analyses were conducted in the present study. A compact tension (CT) model was developed to clarify the feasibility of bonding the SMA patch to the reinforcement of the mode Ⅰ, mode Ⅱ, and mode Ⅲ cracks. On this basis, parametric analysis was conducted to investigate the strengthening parameters, i.e., the bonding area, the thickness, and the strengthening angle of the SMA patch. Subsequently, fatigue tests on the unreinforced steel plate and cracked steel plate strengthened by the SMA patches were conducted. The monitored stress variation, crack propagation behavior, and fatigue fracture surfaces were analyzed. Findings are meaningful to the application of the SMA reinforcement method in practical engineering.

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.

Fatigue strengthening of cracked steel plates with bonded Fe‐SMA strips

AbstractPrestressed fatigue strengthening of steel structures has been proven effective by numerous investigations. Bonded iron‐based shape memory alloy (Fe‐SMA) strengthening has shown a great potential in this regard, however, with limited corroborating studies. Moreover, a proper model for fatigue analysis of systems that are retrofitted with bonded Fe‐SMA strengthening is missing. In this study, an analytical model, coupling prestress analysis and fatigue analysis, is proposed. Four steel plates with central through‐thickness cracks were strengthened with use of bonded Fe‐SMA strips, and subsequently tested under fatigue loading after generating prestress via heating and cooling. The fatigue behavior predicted by the proposed model lies in excellent agreement with the fatigue testing results.

Experimental study on fatigue behavior of cracked steel plates repaired with adhesively bonded steel patches

Fatigue cracking is prone to occur in orthotropic steel decks (OSDs) due to its complex geometry. To guarantee structural safety and extend the fatigue life of OSDs in steel bridges, the repair technique of adhesively bonded steel patches, which has the advantage of lower cost, easy operation, and not damaging the original structure, is experimentally studied using simplified cracked steel plate specimens. Four repair schemes were considered including bare plate, single-sided patched, double-sided patched, and stop-hole repaired. The failure mode, fatigue crack propagation, and adhesive damage were studied to evaluate the effects of steel patch repair. The morphological analysis was performed to investigate the fatigue fracture characteristics and metal interface performance. The outcomes showed that adhesively bonded steel patches could significantly improve the fatigue life of cracked steel plates and the strengthening was more effective for double-sided patched specimens than single-sided patched specimens. In comparison, the repair effect of the stop-hole method is limited for cracked specimens.

Prediction of fatigue crack propagation in center cracked steel plate strengthened with partially covered CFRP strip

Evaluating the fatigue performance of steel members strengthened with carbon fiber reinforced polymer (CFRP) is of great significance for formulating maintenance strategies and making full use of materials. Current analytical models are mainly developed for fully covered CFRP strengthening method without considering different mechanisms at each stage. In this paper, an analytical model considering different stages of crack propagation was proposed to predict the fatigue performance of center cracked steel plates strengthened with partially covered CFRP strips. The strengthening effects of CFRP strips were numerically analyzed based on the extended finite element model (XFEM) calibrated by test data. The validity of the analytical model was checked by several sets of test data and numerical simulations. The results show that the proposed analysis model can reasonably predict the fatigue life of center cracked steel plates strengthened with partially covered CFRP strips. This study may provide a reference for the application of the partially covered CFRP fatigue strengthening method in engineering structures.

Integrating SMA and CFRP for fatigue strengthening of edge-cracked steel plates

Inclined fatigue cracks of U-ribs and diaphragms in orthotropic steel-box girders are challenging to be repaired using prestressing techniques. Integrating shape memory alloys (SMAs) and carbon fibre reinforced polymers (CFRPs) can achieve a hybrid self-prestressing strengthening approach for such fatigue cracks. To examine the strengthening effect of this approach on inclined cracks, 39 specimens were prepared in four groups and tested under static and fatigue tensioning in this study. Both static and fatigue test results showed that SMA/CFRP composite strengthening effectively retard steel cracking. Compared to control specimens, SMA/CFRP composite strengthening enhanced the notch tip yield load by 128% and 111% for specimens with a notch inclination of 0° and 30°, and the corresponding fatigue life by 7.62 and 8.69 times, respectively. Besides, the strengthening effect of combining SMA and CFRP (SMA/CFRP composite) on cracked steel plates was greater than that of either SMA or CFRP alone, particularly for the steel plates with an inclined crack. Finally, the calculation of mixed-mode I/II effective stress intensity factors confirmed the superior strengthening effect of SMA/CFRP composite on steel plates with an inclined crack. The findings of this study can provide a reference for the reinforcement of orthotropic steel-box girders.

Fatigue Repair of Cracked Steel Plates Using Small-Patch Ultrahigh-Modulus CFRP Governed by Bond Failure

This study evaluates the effectiveness of externally bonded small-patch ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) plates of 460 GPa modulus in extending fatigue life and slowing crack propagation in steel plates with simulated fatigue cracks. The study investigates a range of very short bond lengths for applications where bonding space may be limited or accessibility restricted, together with the effect of single- versus double-sided application, on fatigue performance. It also compares short UHM CFRP plates with similar length normal modulus (NM) (165 GPa) CFRP plates with regard to extending fatigue life and reducing stress concentration at the crack tip. Distributed fiber-optic sensors (DFOS) and digital-image correlation (DIC) are used to capture the full strain field and track crack growth. Results showed that fatigue life was increased by up to 2.0 and 2.34 times for single- and double-sided UHM CFRP repairs. As bond length increased from 25 to 100 mm, fatigue life increased from 1.36 to 2.0. UHM CFRP more effectively reduced stress concentration at the crack tip, by 60% compared with 37% for NM CFRP, indicating that it has the potential for superior fatigue life gains, relative to NM CFRP if the necessary bond length to prevent or delay debonding is provided. As debonding failure governed in this study, NM CFRP plates achieved comparable fatigue life extension. DIC tracking of crack growth matched the traditional “beach marking” technique with less than 6% difference.

Prediction of fatigue crack propagation in center cracked steel plate strengthened with prestressed CFRP strip

Evaluating the fatigue behavior of steel structures strengthened with prestressed carbon fiber reinforced polymer (CFRP) is of great significance for structural repair and rehabilitation. In this paper, an analytical model based on linear elastic fracture mechanics considering the additional elongation of the steel plate caused by the central crack opening was proposed to predict the fatigue behavior of prestressed CFRP strips strengthened steel plates. The finite element model calibrated by experiments was used to verify the proposed model. The results showed that the proposed model can predict the stress state of various components, the stress intensity factor SIF amplitude, the fatigue crack growth life, and the minimum prestress of CFRP strips required for crack arrest under different strengthening conditions with high accuracy. This study will be conducive to a better application of the prestressed CFRP strengthening of thin-walled steel structures under fatigue loading.

Numerical Analysis of Tensile Performance of Central Cracked Steel Plates Repaired with CFRP Sheets

Numerical Analysis of Tensile Performance of Central Cracked Steel Plates Repaired with CFRP Sheets

Debonding development in cracked steel plates strengthened by CFRP laminates under fatigue loading: Experimental and boundary element method analysis

Carbon fiber reinforced polymer (CFRP) laminates can effectively enhance the fatigue life of steel structures. However, few studies have investigated the influence of crack-induced debonding in the CFRP-steel interface on the CFRP strengthening efficiency and the relationship of crack propagation and debonding development. This study experimentally and numerically – with the boundary element method (BEM) – investigated crack propagation and debonding development in CFRP-strengthened cracked steel (Q345, Q460, and Q690) plates. The fatigue test specimens were subjected to a maximum stress of 50% steel yield stress and a stress ratio of 0.1, during which real-time changes in CFRP strain distribution were recorded by digital image correlation (DIC). The CFRP strain gradient calculations showed that crack-induced debonding was crack length-dependent. The numerical fatigue life results were in good agreement with the experimental data when considering debonding and overestimated the experimental data without considering debonding, demonstrating the necessity of considering crack-induced debonding in calculation and design. Furthermore, a relationship was obtained between crack propagation and debonding development.

Stress Intensity Factor Assessment for the Reinforcement of Cracked Steel Plates Using Prestressed or Non-Prestressed Adhesively Bonded CFRP.

The use of adhesively bonded carbon fiber reinforced polymer (CFRP) materials to reinforce cracked steel elements has gained widespread acceptance in order to extend the lifespan of metallic structures. This allows an important reduction of the stress intensity factor (SIF) at the crack tip and thus a significant increase of the fatigue life. This paper deals with the assessment of the SIF for repaired cracked steel plates, using semi-empirical analysis and finite element analysis. Metallic plates with only one crack originating from a center hole were investigated. Virtual crack closure technique (VCCT) was used to define and evaluate the stress intensity factor at crack tip. The obtained modeling results are compared with experimental investigations led by the authors for different reinforcement configurations including symmetrical and non-symmetrical reinforcement, normal modulus and ultra-high-modulus CFRP plates, and pre-stressed CFRP plates. Results show that finite element model (FEM) analysis can obviously simulate the fatigue performance of the CFRP bonded steel plates with different reinforcement configurations. Moreover, a parametric analysis of the influence of the pre-stressing level was also conducted. The results show that an increase of the pre-stressing level results in an increase of the fatigue life of the element.

An investigation on the fatigue performance of cracked steel plates reinforced with FRP and stop hole

In this paper, we implement the combined method of drilling stop hole and FRP reinforcement to repair cracked steel plates subjected to cyclic tension. The crack initiation and growth are experimentally investigated. The stress distribution at the stop hole and the residual fatigue life are evaluated by the FEM. The effects on prolonging residual fatigue life are analyzed. The results show that the effectiveness of only using the stop hole is limited, while the combined method has dramatically prolonged the residual fatigue life. The effect mainly owes to the increasing of the crack initiation life from the stop hole.