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The strain gauge method and the digital image correlation (DIC) method are commonly employed for measuring strain in tested objects, including material specimens and structural elements. The optical method enables the assessment of 3D strain fields across the entire area of interest, achieved through cameras and advanced software. The study investigates both quasi-static strength tests and more advanced research of structures. It explores full-scale construction testing, featuring highly stressed components of new wagon designs. The paper reviews the benefits and challenges of using the DIC method to measure large-scale elements. Conducting full-scale object testing is characterized by significant complexity, often involving interactions between elements, complex loading conditions, and the influence of friction. Numerous factors affect the measurements. Therefore, to compare both methods, an initially standard shear by tensile test of CFRP composite was analyzed. The analysis of strain maps provides valuable visualization of deformation patterns occurring during construction loading. The strain gauge method was crucial for verifying the quality of the DIC measurements. The results obtained provide a detailed understanding of how the components behave, highlighting the versatility of digital image correlation technology. For strain values of 0.3% and above, a good match was obtained between optical and strain gauge measurements. Below this value, the results have less accuracy. The results obtained provide a detailed understanding of how the components behave, highlighting the versatility of digital image correlation technology. The error comparison and discussion between different measurement scenarios were conducted. The paper presents a developed methodology for measuring strain and displacement state in complex and crucial structural elements. The method can be applied to measurements of heavily loaded components used in the transportation industry; for example, in railways.
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This study presents an experimental investigation of an in-plane shear of a glass lamina composite using a ±45° off-axis tension test. Typically, the shear stress curve, shear modulus, and in-plane shear strength for composite lamina-type materials are identified. Previous research indicated that a loading rate affects the strength of this composite. This study extends the existing literature by utilising a non-contact optical digital image correlation (DIC) method to measure strain distribution during the test. Two cross-head displacement rates were examined. The obtained strain maps reveal an uneven distribution resembling fabric texture. As the deformation progresses, the differences in the strain pattern increase. Subsequently, a quantitative analysis of the differences between regions with extreme (minimum and maximum) strain values and regions with average values was conducted. Based on these measurements, shear stress-strain curves, indicating variations in their courses, were constructed. These differences may reach several percent and may influence the analysis of numerical simulations. The DIC results were validated using strain gauge measurements, a commonly utilised method in this test. It was demonstrated that the location of the strain gauge installation impacts the results. During the tests, the occurrence of multiple microcracks in the resin was observed, which can contribute to the nonlinearity observed in the shear stress-shear strain curve.
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A material strength investigation along with a detailed microfractography analysis of fractures formed during static tensile tests of steel Armstal 550 was performed. The tests in this research were conducted in a temperature range of 298 to 973 K. In addition, during tensile tests at ambient temperature, optical measurements of strain maps and the curvature of the neck were performed. The minimum cross-sectional diameter and the radius of the neck curvature during tensile tests were obtained. The data can be directly used to obtain the true stress-strain curve. The material property analysis confirmed the high strength of the Armstal 550 alloy. The ultimate strength at room temperature equals 2.14 GPa, whereas the yield point equals 1.65 GPa. A decrease in the strength parameters along with an increase in temperature was noted. This is a typical phenomenon related to a change in the density and thermal expansion of steel under the influence of the temperature increase. For example, at a temperature of 500 °C, the ultimate strength is more than 50% less than at room temperature. An in-depth analysis of the metallography and microfractography of fractures resulting from static tensile tests showed the formation of atypical nano- and microstructures with an elongated shape. Local nano- and microstructures were observed at different levels of intensity for different temperatures. The largest clusters of nanoparticles were present on the surfaces of the specimens examined at a temperature of 973 K. Scanning microscopy analysis confirmed the presence of molybdenum oxides.
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Aramid and polyamide cords are used in a wide range of applications, particularly in the automotive industry (tire reinforcement) and textile industry for military and fireguard purposes. The problem of the reliable experimental study of tensile behavior of synthetic cords is considered in this paper. In the available standards for synthetic cord testing, particularly ASTM D 885-03, the tensile test must result with the cord damage in the middle of gauge length, and the cords should be fixed in the machine clamps. The trial test gave damage near the clamps. We propose a novel testing stage mounted in the testing machine clamps to achieve the uniform tensile stress distribution in the gauge length of the measured cords. The results of the deformations were measured in two ways: using testing machine head displacement and a videoextensometer. Stress curves of four distinguished cords were evaluated and compared. The second method allowed to acquire results differing from the manufacturers' data from 0.7% to 21.5%, which allowed for the conclusion that the designed test stand allows for obtaining reliable results for stretched cords.
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This paper presents the results of the experimental research of 3D structures developed with an SLA additive technique using Durable Resin V2. The aim of this paper is to evaluate and compare the compression curves, deformation process and energy-absorption parameters of the topologies with different characteristics. The structures were subjected to a quasi-static axial compression test. Five different topologies of lattice structures were studied and compared. In the initial stage of the research, the geometric accuracy of the printed structures was analysed through measurement of the diameter of the beam elements at several selected locations. Compression curves and the stress history at the minimum cross-section of each topology were determined. Energy absorption parameters, including absorbed energy (AE) and specific absorbed energy (SAE), were calculated from the compression curves. Based on the analysis of the photographic material, the failure mode was analysed, and the efficiency of the topologies was compared.
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This paper presents the effect of deposited graphene oxide coating on fatigue life of austenitic steel 1.4541 at 20 °C, 100 °C, and 200 °C. The study showed a decrease in the fatigue life of samples with a deposited graphene oxide layer in comparison with reference samples at 20 °C and 100 °C. However, an increase in fatigue life of samples with a deposited graphene oxide layer in comparison with reference samples occurred at 200 °C. This relationship was observed for the nominal stress amplitude of 370 and 420 MPa. Measurements of temperature during the tensile failure of the sample and microfractographic analysis of fatigue fractures were performed. Tests have shown that graphene oxide deposited on the steel surface provides an insulating layer. A higher temperature of the samples with a deposited graphene oxide layer was observed during fracture compared to the reference samples.
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High specific mechanical properties of composites are the reason for their use in various fields, e.g., the aerospace industry. Mechanical joints are still used in the aerospace industry to assembly large aircraft structures. The properties of laminate around the hole can be, however, weakened, compared to their nominal values as a result of a drilling process or cyclic loading. This paper aims at the classification and analysis of imperfections affecting mechanically fastened joints in a laminate structure. A method of modeling the hole vicinity, a gradient material model, as well as the numerical and experimental estimation of laminate deterioration in this area, were proposed and analyzed. Comparative analysis of numerical and experimental results based on displacements of the testing machine grip and the extensometer length confirmed the aforementioned results as consistent in linear ranges. Therefore, joint characteristics obtained based upon measurement of the grip displacement and the ratio of stiffness in linear ranges are sufficient to determine the parameters of a gradient material model. Some imperfections resulting from, e.g., asymmetry, were included in the gradient material model; thus, the obtained weakening of laminate properties in the hole vicinity can be overestimated. Therefore, further analyses of the gradient material model for laminate structures are necessary.
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This paper presents a characterization study of specimens manufactured from Ti-6Al-4V powder with the use of laser engineered net shaping technology (LENS). Two different orientations of the specimens were considered to analyze the loading direction influence on the material mechanical properties. Moreover, two sets of specimens, as-built (without heat treatment) and after heat treatment, were used. An optical measurement system was also adopted for determining deformation of the specimen, areas of minimum and the maximum principal strain, and an effective plastic strain value at failure. The loading direction dependence on the material properties was observed with a significant influence of the orientation on the stress and strain level. Microstructure characterization was examined with the use of optical and scanning electron microscopes (SEM); in addition, the electron backscatter diffraction (EBSD) was also used. The fracture mechanism was discussed based on the fractography analysis. The presented comprehensive methodology proved to be effective and it could be implemented for different materials in additive technologies. The material data was used to obtain parameters for the selected constitutive model to simulate the energy absorbing structures manufactured with LENS technology. Therefore, a brief discussion related to numerical modelling of the LENS Ti-6Al-4V alloy was also included in the paper. The numerical modelling confirmed the correctness of the acquired material data resulting in a reasonable reproduction of the material behavior during the cellular structure deformation process.
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Giant cell arteritis (GCA) is a chronic vasculitis that typically presents with headache, fever and polymyalgia although atypical presentations are known. We present a case of GCA with nonproductive cough and pyrexia of unknown origin emphasizing this atypical nature of presentation. We report a rare association of GCA with granulomatous hepatitis. We also support the use of PET scanning in diagnosing and monitoring this condition.