The damage tolerance of Carbon Fibre Reinforced Polymer (CFRP) to Barely Visible Impact Damage (BVID) is a critical design limiter for composite structures. This study investigated the key driving ...mechanisms and damage evolution of the compressive failure of laminated composites containing BVID using compression after impact and indentation (CAI) tests. Experiments were carried out on two similar quasi-isotropic laminates: 452/902/02/−4522S and 45/90/0/−454S. Matrix cracking and delaminations were introduced by either low-velocity impact or quasi-static indentation tests prior to the CAI tests. The full-field displacement during CAI as well as the moment of rupture was captured by 3D Digital Image Correlation (DIC). The effect of ply-blocking and influence of factors, such as impact energy, delamination area and surface indentation, on compressive failure was studied. Previously validated high-fidelity finite element (FE) numerical models for the indentation and impact events were then used to investigate the damage evolution during CAI failure.
•The impact of MWCNT on properties of regular and high-performance concrete was tested.•Self-sensing as stress detection in regular and HP concrete was compared using cyclic compression.•Crack ...detection was evaluated by combining wedge splitting test with digital image correlation.•The MWCNT addition enhanced stress detection and enabled microcracking detection.
Concrete is the worldwide most utilized construction material because of its very good performance, forming ability, long-term durability, and low costs. Concrete is a brittle material prone to cracking. Extensive cracking may impact durability and performance over time considerably. The addition of a small amount of carbon nanotubes (CNT) increases the concrete’s overall electrical conductivity, enabling internal structure condition monitoring (self-sensing). This article presents the mechanical and self-sensing properties of regular and high-performance concrete (HPC) with multi-wall carbon nanotubes (MWCNT). The stress detection was investigated in cyclic compression, while damage detection was assessed by means of wedge splitting tests combined with the digital image correlation (DIC) method. The results proved that a small addition of MWCNT (0.05% and 0.10%) enhances the stress detection capabilities and enables the monitoring of microcracking.
•An overview of state-of-the-art optical techniques for in-situ evaluating the direct laser deposition (DLD) processes is presented.•The application of digital image correlation (DIC) to in-situ ...characterize deformation of the building part and substrate is reviewed for the first time.•Different types of optical pyrometers for measuring the melt pool temperature (distribution) are categorized and discussed.•The challenges and potential directions of using these optical methods are explored.
Metal additive manufacturing (AM), being a transformational technology with unique capabilities, has received considerable attention from both industrial and academic sectors. To date, quality and repeatability are still regarded as the critical technological barrier that hinders their widespread applications, especially for high-value components with stringent requirements. One significant approach to overcome this formidable challenge is in-process monitoring combined with real-time closed-loop control, which has been explored by great research efforts. This paper describes ongoing work on the in-situ monitoring and characterization during processes of powder-fed laser-aided direct metal deposition (DMD), a form of metal AM. Much emphasis has been placed on the optical techniques, such as the temperature and morphology measurement of the melt pool by two-wavelengths pyrometers, and high-speed CMOS cameras, respectively. In particular, the state-of-the-art with respect to an emerging field-the full-field deformation monitoring of part and/or substrate by digital image correlation (DIC), is addressed.
This paper investigates digital image correlation approaches for assessing speckle patterns produced by surface plasmon resonance (SPR) imaging. An SPR sensor based on the Kretschmann setup ...comprising a gold-coated prism in a fixed angular position performs refractive index assessments in ethanol solutions. Subsequently, the acquisition system collects the reflected light and processes the speckle field images to evaluate the sensor's sensitivity, noise, and limit of detection. Based on three repetitions under similar conditions, the maximum resolution for the average intensity, zero-mean normalized cross-correlation, and the relative sum of square differences metrics are 4.90×10−4, 2.31×10−5, and 7.45×10−6 RIU, respectively, leading to an improved limit of detection without modifying the optical setup.
•Comparison of plasmonic sensing based on intensity detection and speckle comparison.•Experimental validation using ethanol samples dissolved in water.•Detection limit of the order of 7×10−6 RIU using speckles comparison.•First experimental validation using speckles comparison for plasmonic sensing.
In the last few decades, there has been a surge of research in the area of non-contact measurement techniques. Photogrammetry has received considerable attention due to its ability to achieve ...full-field measurement and its robustness to work in testing environments and on testing articles in which using other measurement techniques may not be practical. More recently, researchers have used this technique to study transient phenomena and to perform measurements on vibrating structures. The current paper reviews the most current trends in the photogrammetry technique (point tracking, digital image correlation, and target-less approaches) and compares the applications of photogrammetry to other measurement techniques used in structural dynamics (e.g. laser Doppler vibrometry and interferometry techniques). The paper does not present the theoretical background of the optical techniques, but instead presents the general principles of each approach and highlights the novel structural dynamic measurement concepts and applications that are enhanced by utilizing optical techniques.
•Photogrammetry measures displacements to monitor dynamics of structures.•The paper reviews the most current trends in photogrammetry.•The paper compares the applications of photogrammetry to conventional approaches.•Photogrammetry effectively measures high-displacement and low-frequency vibrations.•Photogrammetry can be applied to measure dynamics of rotating structures.
This paper presents a study on microstructural deformation of a ferritic–pearlitic ductile iron, utilizing in-situ tensile testing, digital image correlation (DIC) and finite element analysis (FEA). ...For this purpose, the in-situ tensile test and DIC were used to measure local strain fields in the deformed microstructure. Furthermore, a continuum finite element (FE) model was used to predict the strain maps in the microstructure. Ferrite and pearlite parameters for the FE-model were optimized based on the Ramberg–Osgood relation. The DIC and simulation strain maps were compared qualitatively and quantitatively. Similar strain patterns containing shear bands in identical locations were observed in both strain maps. The average and localized strain values of the DIC and simulation conformed to a large extent. It was found that the Ramberg–Osgood model can be used to capture the main trends of strain localization. The discrepancies between the simulated and DIC results were explained based on the; (i) subsurface effect of the microstructure; (ii) differences in the strain spatial resolutions of the DIC and simulation and (iii) abrupt changes in strain prediction of the continuum FE-model in the interface of the phases due to the sudden changes in the elastic modulus.
Additive manufacturing (AM) is a special technology that offers several advantages compared to the conventional methodologies. For instance, it allows to build components with complex geometry, ...difficult to make in a different way, build integrated parts deleting joining issues, etc. However, its application in engineering fields is still limited because the dependency between the mechanical properties of the obtained components and the manufacturing parameters is not in depth understood. Improve the performances of AM components, under static and dynamic loadings, is crucial to ensure their durability and reliability and in recent years it became a challenging research field. In this work, the effect of the surface roughness on the multiaxial fatigue resistance of Ti6Al4V thin-walled tubular samples, made by the Selective Laser Melting (SLM) process, was investigated. In particular, experiments under combined axial–torsional loadings were carried out on two batches of samples, made by different surface roughness (machined and as built samples). Maximum valley depth Rv was used as a representative parameter of the surface roughness as it geometrically represents a stress concentration zone where crack initiates and propagates. An effective strain intensity factor range, based on the modified Smith Watson and Topper (MSWT) model, that includes the roughness parameter Rv, is proposed and used for a better correlation of the fatigue data. To prove the reliability of the proposed model, the Socie and the Reddy & Fatemi effective strain-based intensity factor range were also used but a bigger scattering of results was observed. The MSWT model was also applied to predict the failure plane and the obtained results were compared with the predictions of the Fatemi-Socie model. Results revealed that, for SLM Ti6Al4V alloy components, the MSWT model is more accurate.
•Determination of the fracture toughness KIcS in quaternary binder concretes.•Application of Digital Image Correlation (DIC) measurements to analyzed composites.•Two measuring devices were used in ...the studies, i.e. MTS 810 press and DIC system.•Visual analysis of cracks propagation were carried out.•Fracture processes based on the images of major strain were analyzed.
This paper presents comparative measurements of the fracture toughness together with visual analysis of cracks propagation of concretes made of quaternary binders. A composition of the 2 most commonly used mineral additives, i.e. fly ash (FA) and silica fume (SF) in combination with nanosilica (nS), has been proposed as a partial replacement of the ordinary Portland cement (OPC) binder. The primary objective of the proposed tests was to assess: basic mechanical parameters, i.e. compressive strength – fcm and splitting tensile strength – fctm, fracture toughnessKIcS, and fracture processes in quaternary concretes. The modern and precise DIC technique was used, during the studies, in order to realised assumed tasks. It was found that modification of the binder composition with 3 pozzolanic active materials resulted in an increase in the analysed mechanical parameters for each of the combinations compared to the results obtained for the control concrete. Substitution of the binder by 3 additives resulted in a slight heterogeneity of the structure of the quaternary binder concretes. In addition, as content of FA rises throughout each of quaternary concrete series, material becomes more ductile and shows less brittle failure. Therefore composite containing: 80% OPC, 5% FA, 10% SF, and 5% nS – due to its high fracture toughness and lower brittleness – can be used in reinforced concrete structures subjected to dynamic or cyclic loads.
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