Structural Integrity Evaluation Research Articles

Effects of hydrogen and specimen thickness on fracture toughness of ferritic steel welded joint

In this study, fracture behaviors of base metal and weld metal of ferritic steel welded joint in the thick wall pipeline for hydrogen transportation were investigated and the effects of hydrogen and specimen thickness (B) on fracture toughness were comprehensively considered in detail. A series of single edge notched tensile (SENT) tests for base metal and weld metal with B/W (width) ratio of 0.5, 1 and 2 were conducted with and without pre-electrochemical hydrogen charging, and crack tip opening displacement (CTOD) of δm value was obtained by the double clip gauges method. It was found that fracture toughness (δm) of base metal and weld metal decreased with increasing specimen thickness or hydrogenating, and δm of hydrogenating specimen with B/W ratio of 2 was smallest. It was believed that large specimen thickness decreased fracture toughness by constraining plastic deformation at crack tip and restricting dislocations movement, while hydrogen promoted embrittlement by reducing cohesive energy of fracture. In the hydrogenating specimen with larger thickness, there was lower dislocation density near crack tip, leading to a decrease in trapped hydrogen and intensifying the cohesive energy reduction effect, which resulted in reduced δm and the worse fracture toughness, and it means that hydrogen and specimen thickness synergistically affected fracture toughness. In addition, effect of thickness and hydrogen on decreasing fracture toughness was more pronounced for weld metal than base metal, which could be attributed to poorer plastic deformation ability of weld metal and lower dislocation density at crack tip. It is concluded that the hydrogen and thickness effects should be taken into account for the structural integrity evaluation of welded joint in hydrogen transportation pipeline.

Machine Learning Augmentation of the Failure Assessment Diagram Methodology for Enhanced Tubular Structures Integrity Evaluation

Failure assessment diagrams (FADs) are essential engineering tools for evaluating the structural integrity of components. However, their widespread application can be limited by complexity and computational expense. This study presents a novel machine learning-based approach to streamline FAD analysis, offering accuracy and efficiency while overcoming these limitations. The approach integrates numerical contour integral-based FADs with artificial neural networks (ANNs). To ensure reliable material modeling for the Finite Element Analysis (FEA) used to generate J-integral based FADs that train the ANNs, careful experimental and numerical procedures were employed. This involved uniaxial tensile tests, an iterative method for obtaining precise true stress–strain curves, and a Ramberg–Osgood material model for accurate material behavior representation. The ANNs themselves not only analyze large datasets to generate precise FAD envelopes but also predict limit loads and the Φ parameter, incorporating the effect of residual stress on the FAD methodology. To verify and test the proposed method, hypothetical fitness-for-service assessment cases were conducted, incorporating experimental residual stress measurements from split-ring tests on P110 and L80 pipes. These assessments were compared to both traditional FAD methods and computationally intensive FEA-based FADs. Results demonstrate a closer agreement with FEA-based calculations than traditional methods provided in engineering standards. Ultimately, this work provides a rather innovative and adaptable approach for structural integrity evaluations and critical engineering assessments through the proposal of an ANN enhanced FAD approach, simplifying these calculations while maintaining high fidelity.

Development of Strength Evaluation Methodology for Independent IMO TYPE C Tank with LH2 Carriers

Given the inadequate regulatory framework for liquefied hydrogen gas storage tanks on ships and the limitations of the IGC Code, designed for liquefied natural gas, this study introduces a critical assessment procedure to ensure the safety and suitability of such tank designs. This study performed a heat transfer analysis for boil-off gas (BOG) calculations and established separate design load cases to evaluate the yielding and buckling strength. In addition, the study assessed methodologies for both high-cycle and low-cycle fatigue assessments, complemented by comprehensive structural integrity evaluations using finite element analysis. A comprehensive approach was developed to assess the structural integrity of Type C tanks by conducting crack propagation analysis and comparing these results with the IGC Code criteria. The practicality and efficacy of these methods were validated through their application on a 23K-class liquefied hydrogen carrier at the concept design stage. These findings may have important implications for enhancing safety standards and regulatory policies.

Deep Foundation with Driven Precast Concrete Piles and Monitoring with Pile Driving Analyzer PDA

A practical case of deep foundation for an industrial plant in Puerto Natales is presented, using precast reinforced concrete piles that are driven into soft clays (Nspt < 5 blows/ft). Equipment and methods were used for the evaluation of the pile structural integrity and their geotechnical capacity by means of PDA monitoring (Pile Driving Analyzer) during driving. With the results of the PDA test, together with the CAPWAP computational tool, the design hypotheses were verified. During the execution of the project, it was possible to achieve the optimization of the embedment depth and the variation of the required number of piles.

Early Blood-Brain Barrier Impairment as a Pathological Hallmark in a Novel Model of Closed-Head Concussive Brain Injury (CBI) in Mice.

Concussion, caused by a rotational acceleration/deceleration injury mild enough to avoid structural brain damage, is insufficiently captured in recent preclinical models, hampering the relation of pathophysiological findings on the cellular level to functional and behavioral deficits. We here describe a novel model of unrestrained, single vs. repetitive concussive brain injury (CBI) in male C56Bl/6j mice. Longitudinal behavioral assessments were conducted for up to seven days afterward, alongside the evaluation of structural cerebral integrity by in vivo magnetic resonance imaging (MRI, 9.4 T), and validated ex vivo by histology. Blood-brain barrier (BBB) integrity was analyzed by means of fluorescent dextran- as well as immunoglobulin G (IgG) extravasation, and neuroinflammatory processes were characterized both in vivo by positron emission tomography (PET) using [18F]DPA-714 and ex vivo using immunohistochemistry. While a single CBI resulted in a defined, subacute neuropsychiatric phenotype, longitudinal cognitive testing revealed a marked decrease in spatial cognition, most pronounced in mice subjected to CBI at high frequency (every 48 h). Functional deficits were correlated to a parallel disruption of the BBB, (R2 = 0.29, p < 0.01), even detectable by a significant increase in hippocampal uptake of [18F]DPA-714, which was not due to activation of microglia, as confirmed immunohistochemically. Featuring a mild but widespread disruption of the BBB without evidence of macroscopic damage, this model induces a characteristic neuro-psychiatric phenotype that correlates to the degree of BBB disruption. Based on these findings, the BBB may function as both a biomarker of CBI severity and as a potential treatment target to improve recovery from concussion.

Study on the cantilever ratio optimization of high-temperature molten salt pump for molten salt reactor based on structural integrity

The high-temperature molten salt pump is the core equipment in the small modular molten salt reactor with media temperatures up to 700 °C. The cantilever ratio of the molten salt pump is usually large. Excessively large cantilever ratios cause increased deformations and rotational amplitudes at the impeller, thus affecting the operational stability of the main pump; small cantilever ratios cause heavy temperature gradients, thus affecting the structural integrity evaluation. This paper used numerical simulation methods to calculate and analyze the temperature field, stress, and structural integrity, optimized the pump shaft cantilever length of the original scheme based on structural integrity using the dichotomy method, and analyzed the rotor dynamics of the optimization results. The results of this study show that the thermal expansion load caused by the temperature difference has a significant mechanical effect on the structure; the first-order critical speed of the rotor system of the optimized schemes has been improved, and the amplitude of the unbalanced response has been significantly reduced, which not only improves the operational stability of the rotor, also contributes to the compact design of the main pump of a small modular molten salt reactor.

Analysis of crack-tip stress field in unidirectional fiber-reinforced composites based on 3D micromechanical model

Accurately clarifying the influence of cracks on the mechanical behaviors of unidirectional fiber-reinforced composites (UD FRCs) is of great significance for the structural integrity evaluation of UD FRCs with defects. Although several experiments and numerical analyses have explored the impact of cracks on stress field, satisfactory quantitative characterizations of crack size, a/W and location, Δ, fiber content, Vf have not yet been obtained. In this paper, the accurate and detailed microscopic models containing crack were first established and thoroughly validated. Then, a parametric study was conducted using three-dimensional micromechanical analysis to investigate how the crack size and location, fiber content affect the von Mises, stress triaxiality, Lode angle and J-integral of UD FRCs. Results showed that homogeneous models, whether isotropic or anisotropic, cannot accurately describe the mechanical behavior of cracked UD FRCs. The von Mises stress and J-integral are greatly influenced by the crack and fiber content, while stress triaxiality and Lode angle are not sensitive to changes in these factors. Further, the von Mises and J-integral increase with the decrease of Vf and the increase of a/W, but show a more complex trend in the variation of Δ. These findings will help clarify the failure mechanism of cracked UD FRCs and can be used for reliability evaluation.

An enhanced stress field intensity approach for fatigue life assessment combining notch and size effect

The notch characteristics of engineering components significantly impact their fatigue lives. Accurately analyzing the notch effect and size effect is of great significance for structural integrity evaluation, which provides insights into the extent of fatigue failure in engineering structures. In this paper, a new method is proposed for determining the fatigue failure region based on actual elastic–plastic stress distribution under various notch geometries and applied loads. It considers the complex mechanical behavior of the plastic effect and stress relaxation near the notch root. Furthermore, a novel weight function is employed to consider the relative stress gradient at all points within the fatigue failure region. Finally, an enhanced stress field intensity approach is developed to predict notch specimens fatigue lives utilizing experimental lives of smooth specimens. Additionally, the effectiveness of the proposed method is analyzed by predicting the fatigue lives of three distinct materials notched specimens with varying geometries and applied loads. The prediction absolute errors of the proposed approach are compared with those of the other traditional notched fatigue analysis methods. The comparative results indicated that the performance of the proposed method outperforms the other methods.

A Study on the Residual Stress of Seam Pipe Cutting and Girth Welding

Seam pipes are easier to manufacture and cheaper than seamless pipes, and are widely used in the manufacture of pipe spools for marine plant facilities. The manufacturing and assembly of seam pipes involve welding and cutting. The localized heating and cooling that occur during these processes may change the existing residual stress and cause deformation. Uncontrolled deformation can accumulate as assembly errors at the next step, potentially delaying the entire process and causing economic losses. Therefore, characteristics of residual stress redistribution caused by cutting and girth welding of seam pipes need to be studied further. In this study, we performed thermo-mechanical analysis of the manufacturing, cutting, and girth welding processes of seam pipes using the commercial finite element analysis (FEA) software MSC Marc and analyzed the characteristics of residual stress. Furthermore, we measured the residual stress in each process using the hole drilling method, analyzed the characteristics of redistributed residual stress, and ensured reliability. Based on the results of FEA and measured residual stress redistribution, we can provide a basis for reasonable mitigation when performing structural integrity evaluation if there is a defect in the weld of the pipe.

Comparative analysis of binder systems in copper feedstocks for metal extrusion additive manufacturing and metal injection moulding

In the realm of material innovation, the remarkable versatility of thermoplastic-based highly filled composites emerges as a pivotal advantage for fabricating metal parts, seamlessly integrating design flexibility. This study delves into the fusion of design and manufacturing, spotlighting the convergence of material extrusion additive manufacturing (MEX) and metal injection moulding (MIM) processes through the adept utilization of three distinct in-house developed copper-feedstocks. Each feedstock had a different composition that influenced their processability; two feedstocks were for solvent and thermal debinding, and one was only for thermal debinding. The sintering was carried out under the same conditions for all produced specimens to assess the effect of binder composition on the properties of the sintered components. Structural integrity evaluations of sintered specimens encompassed 3-point bending, hardness tests, and metallography. It was possible to perform MEX with all produced filaments and MIM with the pellets of the same feedstocks and to obtain acceptable-quality specimens. Regardless of the shaping method, specimens shaped with binders containing a soluble binder survived the thermal and sintering steps. The specimens produced from the feedstock intended solely for thermal debinding experienced a nearly complete loss of shape during the debinding process. For the specimens that could be debound and sintered without defects, a relative density between ∼88 and 94 % was measured for MEX components and ∼93 and 95 % for MIM components after sintering. All sintered components showed the same diffraction peaks as pure copper powder, confirming that the reductive hydrogen atmosphere provided protection from contamination and reduced the oxides that could have appeared during thermal debinding in air. Moreover, adequate shrinkage of ∼10–18 % was observed in the sintered specimens. Vickers microhardness of the MEX and MIM sintered components were ∼32 HV and ∼36 HV, respectively. Compared to MEX, MIM-produced sintered components showed a higher maximum stress (i.e., σmax = 79 ± 3.2 MPa). These results demonstrate that the binder composition plays a crucial role in determining the success of metal MEX and MIM processes. Having the possibility to choose between MEX and MIM allows for greater design flexibility for copper parts.

Interlaminar and translaminar fracture toughness of 3D‐printed continuous fiber reinforced composites: A review and prospect

AbstractFracture toughness is a critical parameter in the evaluation of a component's structural integrity and damage tolerance. For 3D‐printed continuous fiber reinforced composites (CFRCs) based on the fused deposition modeling (FDM) technique, the fracture behavior differed from that of composites manufactured by traditional processes due to the presence of voids and interfaces at different scales, receiving significant attention. Recently published research attempted to apply various testing standards (for other materials) to investigate the fracture behavior of 3D‐printed CFRCs. In these results, the fracture toughness of CFRCs was influenced by the manufacturing parameters dependent on structural porosity and interfacial bonding quality. This paper reviewed fracture toughness measurement standards compatible with CFRCs, factors influencing fracture behavior, and methods improving the fracture toughness of CFRCs. Lastly, this review explored limitations in current studies focused on fracture toughness measurement of 3D‐printed CFRCs and future perspectives for the fabrication of 3D‐printed CFRCs with improved fracture toughness.Highlights This review focuses on fracture toughness measurement standards compatible with 3D‐printed continuous fiber reinforced composites (CFRCs). The manufacturing parameters influencing fracture behavior and methods improving fracture toughness were summarized. This review explores limitations in current studies focused on fracture toughness measurement of 3D‐printed CFRCs.

Development of fragility models for process equipment affected by physical security attacks

The vulnerability of chemical and process facilities toward physical security attacks depends on the equipment resistance against such attacks and on the performance of Physical Protection Systems (PPS) in place. To enhance the protection against intentional attacks, the development of quantitative vulnerability metrics is essential, nevertheless current standard approaches only offer qualitative or semi-quantitative evaluations. The aim of the present work is to develop a quantitative methodology for the assessment of chemical and process facilities vulnerability towards external acts of interference. The proposed methodology is based both on the evaluation of equipment structural integrity in response to different types of specific impact vectors characterizing intentional attacks and on the quantitative performance assessment of related PPS. In particular, specific fragility models were developed for impact vectors associated with improvised explosive devices, firearms, and incendiary weapons. The novel fragility models were implemented in a comprehensive security vulnerability assessment (SVA) based on Bayesian Networks, in which the contribution of PPS performance was also considered. A case study was defined and analyzed to exemplify the application of the proposed approach. The results obtained allowed for the identification of the most critical security-related escalation scenarios and thus for an improved quantitative SVA.

Study on correlation and scaling protocol between indentation stress-strain and uniaxial stress-strain

Most important mechanical structures produce complex local material changes during the moulding and servicing process. Obtaining the specific local mechanical properties of materials and conducting field tests are problems in structural integrity evaluation. The instrumented indentation technique (IIT) is a solution to these problems. However, the core challenge with the IIT is the quantitative correlation between indentation response and uniaxial stress-strain (USS) response. In this study, we investigate the scaling relationship between indentation stress-strain (ISS) and uniaxial stress-strain (USS). A new protocol for obtaining the mechanical properties of alloy steels using ISS curves is proposed, which can directly obtain the plastic stage of the USS curves from the ISS curves. We used a finite element inversion method based on existing theories. Models with different mechanical properties (USS curves) were established using the ABAQUS software to obtain the corresponding ISS curves. We then explored the relationship between the two; the strain-scaling factor and stress-scaling function were specifically identified. Our work proposes an ISS protocol for power-law-hardening materials. Two alloy steels (SA508 and 42CrMo) were experimentally verifieds. The predicted results are approximately consistent with the practical curves and the error was within ± 10%. Because of the universality and reliability of the protocols, it is expected to provide a theoretical reference and technical approach for the development of IITs and structural integrity evaluation of important mechanical structures.

Using conditional generative adversarial networks for the prediction of stresses in an adhesive composite

AbstractFiber reinforced adhesives are an integral part of wind energy turbine blades and play an important role in evaluation of structural integrity of the blades. Digitization of manufacturing processes and demand for fast and efficient stress analysis argues for the application of deep learning. As a step forward in using deep learning to predict structural properties in composite, the work would explore the applicability of deep learning methods to 2D fiber reinforced composite. In this work, a composite adhesive used in wind energy turbine blades is used as an illustrative example. The composite adhesive when viewed using a CT scan machine shows a heterogeneous structure with two phases, a softer matrix phase and a much stiff fiber phase. For this purpose, several CT scan images of the fiber adhesive composite are used. The images on subsequent FEA analysis serves as the training data for the deep learning framework. Once trained, the neural network would be able to predict the stress distributions in the structure. We apply conditional adversarial networks as general purpose solutions to problems focused on stress prediction, which could be thought of as an image‐to‐image translation from the microstructure domain to the stress domain. These networks in addition to learning the mapping from input image to output image also learn a loss function to train for this mapping. This makes the method more generic because otherwise different loss formulations for different problems have to be formulated.

Seismic evaluation of buried gas pipelines based on the fault slip tendency in South Korea

As numerous earthquakes occur worldwide, securing the seismic performance of infrastructure is important because the damage to buried gas pipelines during an earthquake can cause significant secondary damage. Buried gas pipelines are subject to damage owing to permanent ground movements, one of which is faulting. In this study, the expected displacement of faults caused by earthquakes is predicted by introducing the concept of slip tendency. Using approximately 14,000 fault segments obtained from fault surveys, we calculated the slip tendency based on the Korean Stereonet by region. Thus, the maximum displacement by region that could be triggered by fault reactivation was calculated. A finite-element model of a pipeline passing through a fault zone was developed by varying the actual pipeline used in Korea and various types of geotechnical information. Using this model, a structural analysis of the pipe during fault displacement was performed, and structural integrity evaluation results were derived. The strain value increased as the angle between the pipe and the fault plane increased and as the dense ground and compression-dominated movement increased, confirming this with an application example. Finally, a process capable of evaluating all regions of Korea was established using the displacement values of the predicted fault occurrence by region based on the slip tendency.

Design and Analysis of Solar Car Chassis for WSC 2023

The World Solar Challenger is a biennial global competition that plays a crucial role in testing and advancing the technological limits of solar-powered vehicles, particularly in the context of diverse travel conditions. The competition features three categories: Challenger Class, Cruiser Class, and Adventure Class. In 2023, Siam Technology University participated with the STC-4 model in the Cruiser Class. This research contributed to the vehicle's design, structural integrity, safety, and performance evaluation, essential for passing the scrutineering tests. Researchers were involved in shaping the vehicle's aerodynamics, analyzing structural aspects, and designing safety features compliant with World Solar Challenge 2023 requirements. The goal was to ensure the vehicle's safe participation and successful operation under varied conditions. The designed solar-powered vehicle, STC-4, aimed to address shortcomings from previous competitions. The structural framework, utilizing AISI 4130 steel, met safety standards, with a final weight of 258 kg. Structural testing ensured that the displacement did not exceed 25 mm. Finite Element Analysis confirmed the structural integrity, aligning with the team's objectives. In conclusion, this research significantly contributed to the design and safety aspects of solar-powered vehicles, as demonstrated by the successful participation of STC-4 in the World Solar Challenge 2023 Cruiser Class. The findings highlight advancements in structural design, safety measures, and performance capabilities, emphasizing the importance of continuous innovation in solar vehicle technology.

Calculation of Vehicle Impact Force on Socket Prefabricated Bridge Piers

The design and evaluation of bridge structural integrity following a collision accident heavily depend on the impact force of the vehicle colliding with the bridge piers. Socket prefabricated piers are commonly used in bridge engineering; however, limited research has been conducted on their impact force. To address this issue, this study employs finite element (FE) simulation to investigate the dynamic force and equivalent static force (ESF) of a vehicle colliding with socket prefabricated bridge columns. The study explores various parameters such as socket connection structural parameters, vehicle condition parameters, and pier parameters. Furthermore, the study evaluates four approaches, including the global average approach, local average approach, peak of the 25 ms moving average approach, and simplified pulse approach, to investigate the ESF. Results show that the impact force of the vehicle is significantly influenced by vehicle factors. Additionally, the socket depth of the pier has a great impact on heavy vehicle impacts. A suitable approach for calculating the ESF of a vehicle impacting socket prefabricated bridge piers was identified, and a corresponding calculation formula was developed. The formula is a function of the vehicle's mass and velocity and the pier column socket depth, eliminating the need for cumbersome FE analyses.

Full Scale Bend Test of a Multi Stage Aerospace Vehicle

Evaluation of structural integrity of a missile involves sectional and full scale tests. Tests are carried out for transportation, articulation and aerodynamic loads. Uniqueness of carrying full scale bend test of a multi stage aerospace vehicle lies in the qualification of not only structural integrity of different sections but also the joints. Empty missile structure forms the testing frame. A bending moment envelope is simulated using a combination of upward and downward loads. Design and realization of open configuration test rig frames in order to simulate the necessary boundary conditions was executed. The output measurements for the test are strains, deflections and joint rotation constants. Linear Variable Displacement Transducers (LVDTs) measures the deflections normal to the missile axis and help in mapping of the deflection pattern along the length of the missile. CODs (Crack Opening Devices), developed in-house, are used to measure the joint openings during the bend test. The measured Joint Rotation Constants (JRCs) are in-turn used as input to refine the Finite Element (FE) model, thereby improvising the accuracy of the predicted results from the FE model.

Prediction of transverse welding residual stress considering transverse and bending constraints in butt welding

Welding residual stress is generated by the thermal stress caused by rapid local heating and cooling during welding using a welding heat source. The distribution and size of the residual welding stress are affected by the joint type, welding conditions, constraints, etc., which also affect the fatigue, fracture, and buckling strengths. Therefore, because the magnitude and distribution of residual stress are very important for the safety evaluation of structures, guidelines for structural integrity evaluation suggest a method for deriving the welding residual stress. However, the welding residual stress presented in the guidelines is in a state without constraint; if a constraint exists, it is suggested to use the yield stress of the base material. This can lead to a very conservative design using the yield stress as the welding residual stress in the recent trend of the increasing use of high-strength steels with increased yield stress. Therefore, it is very important to investigate the relationship between constraint and residual stress during welding and to predict the residual stress according to the degree of constraint. In this study, the effects of member thickness, yield stress, lateral constraint, and bending constraint on the welding residual stress in butt welding were investigated, and predictive factors for welding residual stress were established. To this end, a thermal elastic–plastic analysis was performed by changing the thickness, yield strength, lateral constraint, and bending constraint size of the member. Subsequently, the analysis results were used to train a deep neural network (DNN) to predict the residual stress at the center of the weld and toe. In addition, the influence of input factors that affect the prediction accuracy during DNN learning was considered.

A numerical approach to bound the asymmetrically surface-damaged metallic strands response accounting for bending stiffness nonlinearity: Damage and structural integrity evaluation purposes

This study aims to propose an alternative numerical-based methodology to bound the response of asymmetrically surface-damaged metallic strand for damage and structural integrity evaluation purposes. A standard nonlinear finite element algorithm is extended and utilized in which a damaged strand is discretized into uniaxial two-noded nonlinear cable-beam elements in a 3-D space. This extension contemplates accounting for two limit cases regarding the contact regime of the strand wires: (i) stick regime obeying the Bernoulli’s kinematic hypothesis; and (ii) full slip regime leading to a nonlinear bending stiffness. The limit between both contact regimes is given by a critical curvature value associated to the bending response of the damaged strand induced by the asymmetry in surface damage distribution. In this way, the use of the proposed methodology gives rise to a solution space for each parameter of interest namely residual strength, residual linear stiffness, waviness, and fracture energy. The solution spaces are defined by the estimates associated to the purely stick contact regime (Stick model) and the ones that account for the nonlinearity of the bending stiffness (Stick-Slip model). 1 × 7 metallic strands with one and two surface wires cut with diameter values ranging from 1.5 mm to 14.3 mm are used to show the capabilities of the methodology which are validated by comparisons with measured data. Results suggest that curvature boundary layers at strands ends are developed due to the induced bending and that space solutions appropriately bound the measured data. Moderate and high effects on the residual linear stiffness and fracture energy, and waviness parameters due to wires slippage are observed respectively, relative to consider a complete stick contact regime.