Presence Of Internal Defects Research Articles

Comparison of ultrasonic and GPR methods for investigation of reinforced concrete columns

The presence of internal concreting defects such as pores, cavities, sinks, in load-bearing vertical structures can lead to serious consequences, up to accidents. In this regard, it is especially important to identify such defects is an important and relevant task during surveys of load-bearing structures of buildings and structures. At the same time, the search for internal defects is complicated by the fact that they may not be visible on the surface, but may be present in the body of structures. In order to control the quality of the erected monolithic structures, their instrumental examination is carried out with the identification of the possible presence of internal defects by the method of through ultrasonic sounding. The article discusses the comparison of ultrasonic and GPR methods for searching for internal defects in concreting reinforced concrete columns. The studies were carried out on real construction sites in which there were suspicions of internal defects in concreting of high columns. Conclusions are drawn about the possibilities and limitations of the methods. The resolution limits of the methods are presented. The results of the conducted studies show that, despite the relative modern popularity of ground-penetrating radar, ultrasonic methods can work equally well in this type of specific research scenario and have shown a high potential to overcome some inherent limitations of ground-penetrating radar when working with saturated reinforcement.

INFLUENCE OF PARAMETERS OF OPERATING CONDITIONS OF SELECTIVE LASER MELTING ON SPALL FRACTURE KINETICS OF 12Cr18Ni10Ti STEEL

The results are presented with regard to experimental studies of dynamic strength characteristics of samples made of 12Cr18Ni10Ti steel powder. They were obtained through selective laser melting with various parameters of a technological process at shock-wave compression up to pressures of ~7 GPa. Critical parameters of a process, in addition to powder characteristics, include laser operating conditions: a laser spot diameter, laser power, a laser beam scanning velocity, as well as a powder layer thickness, protective atmosphere, etc. It has been demonstrated that an increase in the scan laser power and a decrease in a powder layer thickness bring about a decrease in a number of internal defects in initial structures of samples. The results are given, which compare strength characteristics of these steels with properties of steel produced by a traditional technique of hot rolling. Shock-wave experiments were carried out using a light gas gun-type facility, which makes it possible to accelerate flat impactors to speeds of ~700 m/s; internal wave processes in samples were reproduced when recording a rate of movement of the sample's free surface via a PDV laser interferometer; a degree of spall fracture was determined by the help of a metallographic analysis of samples recovered in tests. It has been showed that steel samples made through a selective laser melting technique have high spall strength and a lower degree of damage compared to hot-rolled steel under the same conditions of high-speed shock loading. According to the results of the metallographic studies, the presence of internal defects in initial structures of samples associated with a choice of operating conditions of a manufacturing process does not affect a degree of their spall damage. At the same time, a wave pattern of shock wave propagation differs significantly for samples with and without defects.

Prediction of the internal structure of a lithium-ion battery using a single ultrasound wave response

This paper describes a means to predict the internal structure of a lithium-ion battery from the response of an ultrasonic pulse, using a genetic algorithm. Lithium-ion batteries are sealed components and the internal states of the cell such as charge, health, and presence of structural defects are difficult to measure. Ultrasonic inspection of lithium-ion batteries is a recent and growing area of research. Reflected and transmitted ultrasound pulses are proposed as a non-invasive means of gaining insights into the internal structure and changes within the closed body of a cell. However, the multiple layers present in a lithium-ion cell are problematic when attempting to interpret waveforms as many internal reflections superimpose. Attributing specific features of a cell to wave characteristics is challenging.In this work a genetic algorithm has been developed as a means to reverse engineer a single ultrasound wave response to predict the internal layered structure of a lithium-ion battery cell. A first randomised guess at the layered structure is made. A numerical wave propagation model is used to predict the ultrasound waveform associated with that structure. This waveform is then compared with a measured or reference waveform to establish its fitness. The layered structure is generationally mutated until the predicted waveforms converge on the reference signal. As this occurs the predicted layered body reveals insights into the cell structure under inspection.Initially, the algorithm was tested against an idealised model battery and its predicted waveform, giving a model-model verification. Further, experimental ultrasonic reflection signals were captured from small capacity lithium-ion cells. Estimations of layer structure predicted by the model were compared with CT-scans of the cells to assess performance. The genetic algorithm was found to be effective in converging the predicted wave response to the reference signal and creating accurate battery structures. It was shown that only part of the waveform was required to generate accurate predictions, which is helpful in avoiding parts of the signal contaminated by near field transducer effects.It was demonstrated that the genetic algorithm can predict material wave speed to 40–1100 m/s (3–29 %) accuracy when battery layer geometry is provided; and thicknesses to within approximately 0.2–7.5 μm (1–13 %) when material properties are provided. Providing the genetic algorithm with parameter constraints; either the layer topology and/or the material properties, substantially improved predictions to estimate the wave speeds on average to approximately ±50 m/s (3–4 %) and the layer thicknesses ±5 μm (7–8 %).This raises the possibility of the use of this approach to predict state of charge when the battery construction is known, or the presence of internal defects and damage to a known battery material composition.

POLYETHYLENE GAS PIPELINES: PRACTICAL POSSIBILITIES TECHNICAL DIAGNOSTICS

Technical diagnostics of in-service polyethylene-exhaust gas pipelines face a number of difficulties, since the existing methods of destructive control are not applicable for determining the mechanical and physical characteristics-stick of polyethylene pipes. The search for effective control methods that can most fully characterize the quality of pipe material and the interpretation of the results obtained are of scientific and practical interest. The article on the example of technical diagnostics of the polyethylene gas pipeline built in 1985 considers possible criteria for assessing the condition of pipes and their ranking by significance. It was found that polyethylene pipes produced during the development of their production did not always meet mandatory quality requirements and could have hidden defects in the form of inhomogeneities, cavities and cracks throughout the volume of pipe material. Based on the experimental studies carried out, it was shown that the pipe material during underground operation does not undergo significant changes in its initial characteristics. At the same time, it was noted that the pipe grades of polyethylene raw materials of the first generation had low resistance to slow crack growth, therefore, the presence of internal defects in the pipe material in owning value with the effect of concentrated loads can lead to premature loss of containment. The work carried out confirmed the possibility of a quantitative design assessment of the technical condition of the gas pipeline based on the results of destructive tests of pipes for long-term hydrostatic strength. The experimental data presented in the article are of interest to specialists who are faced with the need for expert assessment of the state of the pipes of the operated polyethylene gas wires and forecasting their service life.

The Influence of Progressive Cladding Technologies on Layers Quality

Experimental work was focused on the restoration of functional surfaces of shaped parts of the molds for high-pressure casting of aluminum alloys. Paper presents results of the research aimed at determination of the quality of renovation layers applied by laser technology and TOP TIG technology. The TruDisk 4002 solid-state disk laser and the AirLiquide TOPTIG 220 welding power source were used to create the layers. Clad was applied to the base material of nickel-chromium-molybdenum vanadium steel 1.2714, DIN-56NiCrMoV7, with a hardness of 44 HRC. Uddeholm Deivar 1.2344, DIN-X40CrMoV51 wire with a 1.2 mm diameter was used as an additive material. The clad quality was evaluated using the light and electron microscopy and EDX microanalysis. The size of the heat affected zone (HAZ) and the presence of internal defects in the clads were determined. HAZ was set as max. a min. Value. Experimental work was supplemented by evaluation of tribological properties of clads by Pin-on-disc method.

Surface Topography and Biocompatibility of cp–Ti Grade2 Fabricated by Laser‐Based Powder Bed Fusion: Influence of Printing Orientation and Surface Treatments

The selective laser melting process, commonly known as laser‐based powder bed fusion (LB‐PBF), enables the production of structures with unprecedented degrees of freedom that represents an excellent condition for development of metallic implants for biomedical applications. Herein, the effects of laser energy density on relative density and microstructure (presence of internal defects) of cp‐TiGd2 fabricated by LB‐PBF are studied. Additionally, the influence of printing orientation and different surface treatments on surface topography and biocompatibility are investigated. The aim of the research is to develop additive manufacturing process parameters that can achieve full density of cp‐TiGd2 with satisfactory biocompatibility, as a low‐cost alternative to biomedical materials such as Ti–6Al–4 V and Ti–6Al–7Nb. A wide range variation of process parameters leads to an optimized process with high density up to 99.97 ± 0.008%, improved surface roughness, and noncytotoxicity in horizontal and inclined as‐built condition, as well as in Al2O3 (blasting angle 0°) condition.

Benchmark of a probabilistic fatigue software based on machined and as-built components manufactured in AlSi10Mg by L-PBF

The possibility to obtain optimized components with a reduced weight is the main driver of space and aeronautic industries in seriously considering the metal additive manufacturing (AM) technology for production. Despite the incontrovertible advantages offered by this manufacturing technique, the material produced is usually affected by the presence of internal defects, a poor surface quality, and process-induced residual stresses. These features strongly affect the fatigue performance and reproducibility of AMed parts, limiting the adoption of deterministic criteria for fatigue assessment. A probabilistic approach is therefore needed for the analysis of critical and structural components. To this aim, a fully probabilistic finite element (FE) post-processor, ProFACE, was developed by part of the authors to assess the fatigue strength and critical locations of complex components in the presence of process-induced defects. A wide benchmark activity was supported by the European Space Agency (ESA) to test the software capabilities for the life prediction of components manufactured in AlSi10Mg by L-PBF. After tuning ProFACE parameters based on the results obtained on standard fatigue specimens, the software was used to estimate the fatigue life of the components obtaining a good description of the experimental dataset for both volumetric and surface defects. The software was then used to explore the effect of the variability of the most significant parameters affecting fatigue strength of AlSi10Mg AMed components.

<i>In Situ</i> Monitoring of Internal Defects by a Laser Sensor for CMT Based Wire-Arc Additive Manufacturing Parts

Cold metal transfer (CMT) based wire-arc additive manufacturing (WAAM) is increasingly popular for the production of large and complex metallic parts because of its high efficiency and low cost. The presence of internal defects in fabricated parts is a common and critical issue to the process, which degrades parts’ mechanical properties. However, the in-situ monitoring of internal defects can hardly be implemented through traditional inspection techniques due to the surface waviness and the high interlayer temperature of parts. In this study, based on the scan of each deposited layer by a laser sensor and the geometric criteria proposed, an in-situ monitoring method is developed for identifying internal defects, which can be easily applied in an automated WAAM system. Experimental results show that the developed in-situ monitoring identifies 100% accurately the parts without internal defects, and in the cases of parts with internal defects, defective layers can be identified with an accuracy of 93.2%. The effects of process parameters on internal defects have also been investigated.

Study of reaction-bonded silicon carbide samples using visual-optical and radiographic methods of nondestructive control

Products based on silicon carbide are widely used in different industrial applications due to a high level of their mechanical, thermal, and operational properties. When the reaction sintering procedure is used to obtain silicon carbide materials, the preformed porous samples consisting of silicon carbide powders, carbon filler, and coke binder are subjected to liquid-phase silicizing (silicon melt infiltration (MI) in a vacuum furnace. We present the results of studying samples of reaction-bonded silicon carbide (RBSC) using visual-optical and radiographic methods of non-destructive control. Silicizing of carbon-silicon carbide materials can result in formation of defects on their surface and in the bulk of the material. The visual-optical method is shown to be rather simple and extremely informative procedure which ensures the detection of surface defects in the form of pores, cracks, chips, shells, and can also provide indirect indications of possible presence of internal defects in the form of underimpregnated areas. The samples silicized with a larger number of silicon drops on their surface exhibit a higher density and a smaller number of underimpregnated areas which can be detected using radiographic control. X-ray control carried out for several exposures differing in the angle of sample rotation by 90° provided 95%-probability of detecting internal volumetric and planar defects. The results obtained can be used in the manufacture of RBSC-based parts of tribotechnical duty, shut-off valves and other wear-resistant products.

Fatigue failure mechanisms for AlSi10Mg manufactured by L-PBF under axial and torsional loads: The role of defects and residual stresses

Additive Manufacturing (AM) is with no doubt the most revolutionary manufacturing process developed in the last two decades. Despite the indisputable advantages of this technology, the poor surface quality of net-shape components, the presence of internal defects and the development of process induced residual stresses still represent the main problems for the fatigue strength of critical stressed components. In previous works investigating the same alloy, the uniaxial fatigue strength of both machined and net-shape specimens was correlated with the defect size through a Kitagawa diagram, allowing to describe the problem from the threshold perspective. The aim of this work is to extend this approach by investigating the failure mechanisms under torsion in presence of manufacturing defects, both volumetric and superficial anomalies. Specimens manufactured with laser powder bed fusion (L-PBF) technique out of AlSi10Mg, featuring both machined and net-shape surface state, were tested and analysed. The two experimental campaigns allow to investigate the competition between internal defects and superficial features and their effect on the fatigue performances. Tests were performed under two loading conditions, namely fully reverse torsion (RT=−1) and positive torque ratio (RT=0.1). It was found that for the net-shape specimens manufacturing residual stresses have a key role in influencing fatigue strength of this material, making the fatigue limit in torsion of the two considered loading conditions comparable. All the tested specimens failed onto a maximum principal stress plane, which is in line with multiaxial tests performed on a cast A356-T6 aluminium alloy. In some relatively high shear stresses there is a competition between Mode I and Mode II crack propagation, whose threshold condition is controlled by ΔKth,I.

SLM process parameters effects on the fatigue strength of AMed Inconel 718

Selective Laser Melting (SLM) emerged as a technology suitable for the industrial production of structural components featuring complex geometries. In the field of elevated temperature applications, the possibilities offered by the SLM can be successfully used to produced complex geometries as internal cooling channels or lattice structures, as long as the process doesn’t jeopardize the mechanical properties, in particular the fatigue strength.The SLM process parameters play a fundamental role in determining the mechanical performances of the component but are also the key parameter for increasing the productivity of the process and thus the industrial spread of the technology.In the present work, it is presented an experimental assessment of the effects produced by different sets of productivity-oriented SLM process parameters on the Wöhler curves of cylindrical plain specimens. The adopted process parameters were defined on the basis of a previously developed thermal analytical model aimed to predict the melt pool dimensions and shape.HCF tests were carried out at room temperature in an axial load configuration with a stress ratio of 0.05 and a loading frequency of about 150 Hz, by using a resonant testing machine. Test frequency was monitored to detect the occurrence of crack nucleation and monitor the propagation phase.In order to understand the causes of the fatigue behavior, metallographic analyses were carried out to investigate the microstructural properties or the presence of internal defects, i.e. porosity and hot tearing cracks, produced by each set of process parameters. The surface quality was also investigated in detail through optical microscope analyses. Fractographic analyses were used to identify the nucleation and crack propagation region, as well as the presence of the defects in proximity to the fracture onset.

Horn failure prediction in presence of internal defect in ultrasonic machining process through numerical investigation

Horn failure prediction in presence of internal defect in ultrasonic machining process through numerical investigation

SEGMENTATION OF ADDITIVE MANUFACTURING DEFECTS USING U-NET

Abstract Additive manufacturing (AM) provides design flexibility and allows rapid fabrications of parts with complex geometries. The presence of internal defects, however, can lead to deficit performance of the fabricated part. X-ray Computed Tomography (XCT) is a non-destructive inspection technique often used for AM parts. Although defects within AM specimens can be identified and segmented by manually thresholding the XCT images, the process can be tedious and inefficient, and the segmentation results can be ambiguous. The variation in the shapes and appearances of defects also poses difficulty in accurately segmenting defects. This paper describes an automatic defect segmentation method using U-Net based deep convolutional neural network (CNN) architectures. Several models of U-Net variants are trained and validated on an AM XCT image dataset containing pores and cracks, achieving a best mean intersection over union (IOU) value of 0.993. Performance of various U-Net models is compared and analyzed. Specific to AM porosity segmentation with XCT images, several techniques in data augmentation and model development are introduced. This work demonstrates that U-Net can be effectively applied for automatic segmentation of AM porosity from XCT images with high accuracy. The method can potentially help improve quality control of AM parts in an industry setting.

Failure Studies on Adhesive Bonded and Bolted Joints of Natural Fiber Composites

Composites with natural fibers as reinforcements are playing a vital role in recent developments. The present work deals with the fabrication of okra and empty fruit bunch banana fiber polyester matrix composites with varying reinforcement content (5%, 10%, and 15%). Composites were fabricated by using the hand layup technique. After the fabrication process, composites were then adhesively bonded and also joined with bolts. The main objective of this work is to analyse the failure studies on adhesive bonded and bolted joints of okra and empty fruit bunch banana composite specimens. The specimens were tested under tensile load, flexural creep studies, and SEM analysis. It has been observed that empty fruit bunch banana fiber composites exhibited better joint strength properties under tensile loading when compared to the okra fiber composites. To estimate the flexural creep behaviour, all the samples were tested at a constant load of 2.5kg and 5kg. The deflections obtained during regular time intervals (four months) were noted. The presence of internal defects and void content was observed by using the scanning electron microscope. The results showed that adhesive-bonded composites were exhibited less deflection compared to the bolted joints. The empty fruit banana fiber composites exhibited higher creep than okra fiber composites. Decreased creep with the increased fiber has been observed in both cases. SEM Adhesively bonded joints possessing better sustainability as compared to the bolted joints in both the fiber-reinforced composites.

Fatigue behaviour of PBF additive manufactured TI6AL4V alloy after shot and laser peening

Additive manufacturing (AM) of metallic parts is a relatively new manufacturing procedure. Many industry sectors, such as the aerospace or automotive sectors, have started to apply this technology to produce some elements, thus reducing costs and weight. Several metallic alloys have been employed for AM. Due to the high strength-to-density ratio, Ti6Al4V alloy is probably the alloy most used for AM in the aerospace industry. This alloy usually shows good static strength properties. However, the presence of internal defects and the surface roughness result in a fatigue strength that is clearly lower than that of materials produced by traditional processes. Moreover, the scatter of the fatigue results is generally higher than in the case of wrought pieces.Different treatments have been proposed to improve the fatigue behavior by reducing internal defects and roughness or generating a favorable residual stress field. In this work, selected surface treatments were considered to improve the fatigue strength of AM parts, including shot and laser peening as well as a combination of shot peening plus chemical assisted surface enhancement (CASE®). Three groups of specimens, each with one of the surface treatments, were fatigue tested to compare the results produced by these treatments. The residual stresses, roughness and hardness produced by the treatments were analyzed. After testing, the fracture surfaces were also analyzed to better understand the fatigue process of the different groups of specimens. The results indicate that laser peening produced the best results, followed by shot peening plus CASE and shot peening. In all three cases, the fatigue strength was much higher than that of the reference group without surface treatment. It was also observed that all failures initiated from an interior defect in the shot peening plus CASE group, four out of six failures in the laser peened group, but only one failure in the case of shot peened group and none in the reference group. Failures of specimens with initiation from internal defects started from defects located deeper than the compressive residual stress layer produced by the treatments.

Innovation of Biomass Crusher by Application of Hardfacing Layers

This paper presents the innovation possibilities of the crushers functional parts and the results of layers’ renovation analyses of the surfaces worn by biomass crusher hammers. The worn functional surfaces of hammers made of Hardox 400 material were renovated by manual arc welding method (welded with a filled wire electrode with its own protection). As an additive material, Lincore 60-O tubular wire from Lincoln Electric was used. The quality of weld layers was assessed on the metallographic sections, where the presence of internal defects was monitored, and the microstructures of welds were identified. In addition to the metallographic analysis, the microhardness in terms of EN ISO 9015-2 was assessed. Based on the performed experiments, it is suitable for the crusher innovation to recommend the chain replacement with a shaped weldment made of Hardox 400 material, the weldability of which is very good, and to make at least one hardfacing layer on its functional surfaces. With this innovation, the service life of the crushing segment could be extended by more than ten-fold.

Effect of Hammer Type on Generated Mechanical Signals in Impact-Echo Testing.

The impact-echo diagnostic method is a well-known nondestructive pulse compression test method, which can be relatively easily used for the testing of concrete and reinforced concrete elements. The evaluation of the measurement with this method is based on the analysis of the signal itself in the time and frequency domains. This allows acquisition of information on the velocity of the mechanical wave, the resonant frequency of the specimen or on the presence of internal defects. The ability to interpret these measurements depends on the experience of the diagnostic technician. The advent of classification algorithms in the field of machine learning has brought an increasing number of applications where the entire interpretation phase can be considerably simplified with the help of classification models. However, this automated evaluation procedure must be provided with the information of whether the signal acquired by the test equipment has actually been measured under optimally set conditions. This paper proposes a procedure for the mutual comparison of different measuring setups with a variable tip type, hammer handle and impact force. These three variables were used for a series of measurements which were subsequently compared with each other using multi-criteria evaluation. This offers a tool for the evaluation of measured data and their filtering. As an output of the designed method, each measurement is marked by a score value, which represents how well the acquired signal fit the weight demands for each observed feature of the signal. The method allows the adjustment of selected demands for a specific application by means of set thresholds. This approach enables the understanding of characteristics of the signal in the automated pre-processing of measured data, where computing power is limited. Thus, this solution is potentially suitable for remote long-term observations with sensor arrays or for acoustic emission signals pre-processing.

Anisotropic mechanical and fatigue behaviour of Inconel718 produced by SLM in LCF and high‐temperature conditions

AbstractAdditive manufacturing (AM) is one of the processes with the most potential for producing components used in internal combustion engines and features high efficiency due to the possibility of building very complex shapes. Several drawbacks of parts produced using AM are still unresolved, like poor surface quality, the presence of internal defects and anisotropic mechanical behaviour, which all contribute to decreasing the fatigue strength compared with the material produced using conventional processes. The effect of building direction on both the macroscopic mechanical behaviour and the crack propagation mechanism of Ni‐base superalloy Inconel718 produced using AM was investigated under the combined effect of low cycle fatigue (LCF) and high temperature. The different crack growth mechanisms investigated using compact tension (CT) specimens, tested at high temperature, showed a significant difference between the two building directions. The LCF fatigue experiments also showed a significant difference in the ε‐N curves from the two directions together with a high level of scatter due to the dispersion of the defect size at the fracture origin. The dimensions of the defects (as measured using the parameter) were analysed by means of extreme value statistics and showed a significant difference between the two orientations investigated. The aim of this work is to propose a simplified approach (based on ΔJeff concepts) to estimate the fatigue life of a component produced using AM that takes into account the material variability due to the combined effect of mechanical anisotropic behaviour and the presence of defects at high‐temperature conditions.

Acoustic Testing in the Technology of Production of Construction Ceramics with Reinforcing Additives

The behavior of the sound spectrum of free vibrations of cylindrical ceramic samples for light yellow face bricks is interpreted depending on the firing conditions, as well as on reinforcing additives of finely milled fiberglass wastes. A correlation of the frequencies and relaxation times of vibrations with the presence of internal defects and the compressive and bending strengths is found. A testing methodology that reduces the costs of industrial scaling-up of such a reinforcing technology for construction ceramics is proposed.

Investigation of Composite Materials Impact Damage by a Computer Tomography

In this paper, a complex study of composite materials of different nature for the presence of internal defects after the application of impact damage was carried out. The dependence of the initiation energy on material damage from the magnitude of the impact energy is obtained. The areas of sample bundles were investigated by ultrasonic testing (UT). The structure of samples from composite materials was monitored using an industrial microtomography system. A technique was developed that allows highly accurate determining the size of internal sample defects by means of computed tomography (CT).