Observation of Material Degradation under Fatigue and Static Loading Condition Using Selected Electromagnetic NDT Methods

The stability control of surrounding rock for large or super-large section chamber is a difficult technical problem in deep mining condition. Based on the in-site geological conditions of Longgu coal mine, this paper used the dynamic module of FLAC3D to study the response characteristics of deep super-large section chamber under dynamic and static combined loading condition. Results showed that under the static loading condition, the maximum vertical stress, deformation and failure range are large, where the stress concentration coefficient is 1.64. The maximum roof-to-floor and two-sides deformations are 54.6 mm and 53.1 mm, respectively. Then, under the dynamic and static combined loading condition: (1) The influence of dynamic load frequency on the two-sides is more obvious; (2) The dynamic load amplitude has the greatest influence on the stress concentration degree, and the plastic failure tends to develop to the deeper; (3) With the dynamic load source distance increase, the response of surrounding rock is gradually attenuated. On this basis, empirical equations for each dynamic load conditions were obtained by using regression analysis method, and all correlation coefficients are greater than 0.99. This research provided reference for the supporting design of deep super-large section chamber under same or similar conditions.

The present article is focused on the non-destructive testing (NDT) inspection of pipelines during operation namely Magnetic Flux Leakage (MFL) method and Phased Array ultrasonic (PA) method. MFL inspection technique is electromagnetic test method primarily used to detect flaws or defects in high-permeability of ferromagnetic metals such as carbon steel tubing, plate, wire rope and tubular parts. PA ultrasonic method is an advanced NDT method that is used to detect component failures i.e. cracks or flaws and thereby determine component quality. Due to the possibility to control parameters such as beam angle and focal distance, this method is very efficient regarding to the defect detection and speed of testing. In this article real pipeline defect was identified by MFL method in the internal pipe inspection. This defect was fully mapped by Phased Array ultrasonic method in the terrain. 3D model of defect in the tested material was created from measured data and obtained by PA method. The real dimensions of the defect determined from measurements by the method of MFL and PA are compared.

Application of Magnetic Flux Leakage (MFL) method to non-destructively characterize the microstructure and corrosion behaviour of API X65 grade steel

In this study, a novel analytical model is developed to predict the service life of generator rotor fan blades under both static and fatigue loading conditions. The static model assesses failure using a failure assessment diagram (FAD) based on fracture mechanics by calculating the fracture and load ratios. In the fatigue model, forging defects are initially represented as cracks with defined geometries based on available empirical relationships. Critical regions are then identified based on the stress distribution in the blade under cthe generator’s cyclic loading condition. The blade’s service life is subsequently estimated using Paris’ law, fracture toughness, and crack growth constants, taking into account the critical crack size and the number of load cycles. The results reveal that the lowest safety factor for the blade occurs under static loading conditions, with a value of 2.02.

The stress distribution around constructions in deep rock can be modified by dynamic disturbances, such as earthquakes. For this, we proposed a new loading method applied to granite sample under coupled static and dynamic cyclic loading (CSDCL) condition. The variations in P-wave velocity, gas permeability, and mechanical properties of granite before and after CSDCL are revealed. It shows that with increasing axial static stress, the dynamic cyclic loading amplitude and cycle number, P-wave velocity, uniaxial compressive strength (UCS) and elastic modulus decrease, whilst the permeability and Poisson’s ratio increase. It seems that variations in those parameters have a close relation with the exciting frequency. In this case, CSDCL is applied for crack development along the axial direction in the rock samples, and subsequently results in degradation of mechanical properties, delay of P-wave propagation, and increase of the transport paths. The results show that the permeability and Poisson’s ratio are likely to be more sensitive to the CSDCL, in particular under the axial static stress. The empirical relationships of the P-wave velocity with permeability, UCS, and elastic modulus are established for a pragmatic monitoring purpose. From design point of view, we have established the relationships of the disturbance factors to damage variable. Then the correlations of the damage variable to permeability, UCS, and elastic modulus are analyzed. The testing results in this context could facilitate our understanding of rock stability upon excavation subjected to dynamic disturbances.

Natural gas, which is one of the nation’s cheapest forms of energy, is transported to consumer sites via a vast transmission pipeline network .Safety considerations and a desire to assure uninterrupted energy supply require that the pipelines be inspected periodically. The effective detection of defects in the pipeline is vital to assure the integrity of the transmission systems. A variety of nondestructive evaluation techniques (NDE), such as ultrasonic, eddy current, and magnetic flux leakage (MFL) methods have been employed to detect defects in gas pipelines [1]. Among these methods, the MFL method represents the commonly used technique.

The application of magnetic flux leakage (MFL) methods to the nondestructive evaluation (NDE) of metal parts has been known for several decades. The inspection of large-diameter cables (O ≥ 100 mm), such as bridge stay cables, is a new field of application for the MFL method. The large cross-section of the cables requires the generation of strong magnetic fields in order to obtain the induction fields necessary for an accurate inspection of the cables. A new device for the inspection of stay cables has been developed in order to meet the requirements given by the size of the cables. Measurements performed with the developed device on full-scale specimens in the laboratory and first calculations confirm the validity of the MFL approach to the inspection of bridge stay cables. The equipment was used satisfactorily in 2001 for the NDE inspection of the 68 locked coil stay cables (121 mm < O < 167 mm) of a bridge in Southeast Asia. For such cables, no exact localization within the cross section was performed. Thus far, an accurate indication of the position of the detected flaws along the length of the cables could be given. A qualitative statement about position and size of the flaws within the cross section of the cable could also be made. Given the large steel cross-section of the cables, no other nondestructive method to confirm the findings could be applied to assess the exact size and position of the detected flaws. The proposed analytical method presented in this paper makes it possible to increase the amount of information that can be extracted from the measured MFL data with regard to the exact location of the detected flaws within a cross section of a stay cable.

Construction of tall buildings is most common in this twentieth century. Technological development and the modern equipment have reduced the complications in design, analysis and construction of these structures. The seismic damages in these structures are unavoidable unless they are technically designed to be stable or isolated from seismic actions. The energy absorption and energy dissipation in these buildings change based on infill type, openings in infill and interface type used under different loading actions. It is essential to study the combined behaviour of RC main frame and the non-load-carrying structural elements under static and cyclic loading conditions. In this study, an analytical work is carried out using finite element modelling software to understand the performance of multi-storey reinforced concrete (RC) frame, RC frame with infill and infill frame with pneumatic interface pressures (in psi). The structural parameters like load-carrying capacity, maximum displacement, stresses and stiffness under static loading conditions are compared with the RC bare frame.KeywordsRC frameMasonry infillPneumatic interfaceLateral load

Corrosion of the bottom of the petroleum tank may lead to a product leak that could cause a fire or explosion resulting in damage to people and the environment, therefore the test of tank bottom corrosion is necessary to be conducted periodically to prevent the occurrence of the above problems. In non-destructive inspection, the Magnetic Flux Leakage (MFL) method relies on the variation of fluxes caused by defects on the surface of materials to detect corrosion, pitting, or imperfections, which is proved quite effectively with low cost. The project was implemented to develop a prototype of the MFL bottom detection device based on the research results in the world to improve corrosion survey capacity in industrial equipment, as well as to improve the expertise in the Research Team of electronics and automation in the fields of magnetic fields and sensors. As a result, an MFL model using permanent magnets and Hall sensors were fabricated. Survey experiments showed that the machine could detect corrosion defects up to 20% of steel wall thickness in the scanning speed range from 500 mm/s to 1130 mm/s. However, to meet the actual survey needs, the team must continue to improve the device in terms of sensitivity, scanning speed, the ability to operate automatically or semi-automatically, and register for a fire safety inspection.

Welded thermoplastic and adhesively bonded joints are expected to retain a significant proportion of their load bearing capacity for the entire duration of the service life of the joined system. However, service conditions can often involve exposure to static and/or cyclic fatigue loading conditions. Fatigue damage can be particularly harmful to the structural integrity of bonded joints, shortening the life expectancy of the joined system by considerable margins, and is known to occur at relatively low stress levels, particularly in the presence of hostile environments. Similarly, premature failure can occur in bonded joints and welded thermoplastics under static loading conditions with deformation occurring at relatively low loads. This Good Practice Guide is intended to give guidance on fatigue testing of adhesively bonded joints and creep testing of bonded joints and welded thermoplastics for generating design data and for quality assurance purposes. The document is primarily concerned with structural adhesives and thermoplastics.

: Crack tip deformations and fracture parameters in functionally graded glass-filled epoxy beams are experimentally evaluated under static and dynamic loading conditions. Beams with unidirectional, monotonic elastic gradients and cracks along the gradient are examined. SEN samples with increasing or decreasing Young's modulus ahead of the crack tip are studied in symmetric four-point bending and one-point impact loading configurations. Optical method of Coherent Gradient Sensing (CGS) is used to measure crack tip deformations prior to crack initiation. For impact loading experiments, CGS is used in conjunction with high-speed photography for recording instantaneous deformation fields. Stress intensity factors (SIF) or SIF-histories in functionally graded materials (FGM) based on locally homogeneous material descriptions in the immediate crack tip vicinity are evaluated and compared with companion finite element simulations. The influence of elastic gradients in FGM samples with cracks on the compliant and stiff sides of the beam are quantified relative to their homogeneous counterparts and with each other. Under static loading conditions, the crack tip located on the compliant side of the beam is elastically shielded when compared to the situation when the crack is on the stiffer side of the same FGM beam. Under dynamic conditions, however, elastic gradients affect crack initiation differently. Crack initiation in an FGM with a crack on the stiff side of the beam and impact occurring on the compliant edge is delayed when compared to the opposite configuration. Independent finite element simulations of FGMs with idealized elastic gradients with identical crack tip elastic properties suggest that lower crack tip loading rate in the former is responsible for the differences.

An improved classification approach is proposed to solve the hot research problem of some complex multiclassification samples based on extreme learning machine (ELM). ELM was proposed based on the single‐hidden layer feed‐forward neural network (SLFNN). ELM is characterized by the easier parameter selection rules, the faster converge speed, the less human intervention, and so on. In order to further improve the classification precision of ELM, an improved generation method of the network structure of ELM is developed by dynamically adjusting the number of hidden nodes. The number change of the hidden nodes can serve as the computational updated step length of the ELM algorithm. In this paper, the improved algorithm can be called the variable step incremental extreme learning machine (VSI‐ELM). In order to verify the effect of the hidden layer nodes on the performance of ELM, an open‐source machine learning database (University of California, Irvine (UCI)) is provided by the performance test data sets. The regression and classification experiments are used to study the performance of the VSI‐ELM model, respectively. The experimental results show that the VSI‐ELM algorithm is valid. The classification of different degrees of broken wires is now still a problem in the nondestructive testing of hoisting wire rope. The magnetic flux leakage (MFL) method of wire rope is an efficient nondestructive method which plays an important role in safety evaluation. Identifying the proposed VSI‐ELM model is effective and reliable for actually applying data, and it is used to identify the classification problem of different types of samples from MFL signals. The final experimental results show that the VSI‐ELM algorithm is of faster classification speed and higher classification accuracy of different broken wires.

Internal pipeline corrosion can be a major risk factor for pipeline operations. To facilitate the monitoring of Shallow Internal Corrosion (SIC), an In-Line Inspection (ILI) tool based on Eddy Current (EC) technology has been developed. Several cases exist where the prevalent growth of internal metal loss corrosion is the major risk for pipeline operation. One important example is Top of the Line Corrosion (TLC) in wet gas pipelines due to high water condensation rate. Heavy wall pipelines, which are common in offshore applications, are often used to allow a specified maximum corrosion growth rate over the life time of the pipelines. A good approximation even of marginal corrosion growth rates to monitor the degradation process is thereby required. This estimation can be subsequently used to predict pressure that causes failures and shorten pipeline lifetimes in the context of limited state design guidelines. The presented EC technique gives a depth measurement of metal loss defects in terms of absolute figures that complements relative wall loss measurements of Magnetic Flux Leakage (MFL) tools. By inspection of heavy wall pipelines in offshore applications, SIC tool measurement results can outperform MFL depth sizing of shallow internal corrosion, or likewise assist MFL defect identification or depth sizing e.g. by increased distinction of individual pits in dense clusters due to its high lateral resolution of defect surface measurement. Following the combined inspection approach, both measurement methods complement one another and show synergetic effects, which can be used to increase overall sizing performance for corrosion growth monitoring. Results of ILI tool pull tests that are in lines with TLC incidents demonstrate the value of combined action and evaluation of MFL and SIC techniques.

The Magnetic Flux Leakage (MFL) visualization technique is widely used in the surface defect inspection of ferromagnetic materials. However, the information of the images detected through the MFL method is incomplete when the defect (especially for the cracks) is complex, and some information would be lost when magnetized unidirectionally. Then, the multidirectional magnetization method is proposed to fuse the images detected under different magnetization orientations. It causes a critical problem: the existing image registration methods cannot be applied to align the images because the images are different when detected under different magnetization orientations. This study presents a novel image registration method for MFL visualization to solve this problem. In order to evaluate the registration, and to fuse the information detected in different directions, the mutual information between the reference image and the MFL image calculated by the forward model is designed as a measure. Furthermore, Particle Swarm Optimization (PSO) is used to optimize the registration process. The comparative experimental results demonstrate that this method has a higher registration accuracy for the MFL images of complex cracks than the existing methods.

A generalized damage model for woven ply laminates under static and fatigue loading conditions