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Extrusion-based printing of cementitious materials represents an innovative technology in civil engineering. The additive manufacturing process significantly influences the material properties in the hardened state, leading to anisotropic behaviour in terms of stiffness and strength compared to conventionally cast concrete. This experimental study aims to deepen the understanding of the mechanical behaviour of hardened printed concrete. Beam-like specimens with varying printing patterns, loading orientations and lengths are investigated within three-point bending tests (3PBT) and uniaxial compression tests (UCT). Homogenized material parameters such as Young's modulus, compressive and flexural tensile strength and density are statistically evaluated using optically measured displacement and strain fields on the specimen surface. The qualitative and quantitative results demonstrate a strong dependency of material properties and failure mechanisms on the printing pattern. The interfilamental and interlayer areas with weak adhesion are identified as the main reason for anisotropy. [ABSTRACT FROM AUTHOR]

This paper shows the three-point bending strength analysis of a composite material consisting of polyamide doped with chopped carbon fiber and reinforced with continuous carbon fiber produced by means of the material extrusion (MEX) additive manufacturing technique. For a comparison, two types of specimens were produced: unreinforced and continuous fiber-reinforced (CFR) with the use of carbon fiber. The specimens were fabricated in two orientations that assure the highest strength properties. Strength analysis was supplemented by additional digital image correlation (DIC) analysis that allowed for the identification of regions with maximum strain within the specimens. The utilization of an optical microscope enabled a fractographic examination of the fracture surfaces of the specimens. The results of this study demonstrated a beneficial effect of continuous carbon fiber reinforcement on both the stiffness and strength of the material, with an increase in flexural strength from 77.34 MPa for the unreinforced composite to 147.03 MPa for the composite reinforced with continuous carbon fiber. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The industrial sintering process used to produce metallic matrix pads has been altered to diminish the amount of copper used. Unfortunately, replacing a large part of the copper with iron seems to have reached a limit. In the high-energy, emergency-type rail braking used in this study, the materials are put to the very limit of their usage capacity, allowing us to observe the evolution of the microstructure and mechanical properties of sintered, metallic matrix pads. After the braking test, their compressive behaviour was assessed using digital image correlation (DIC), and their microstructure with scanning electron microscopy (SEM). The worn material has three flat layers with different microstructures and compressive behaviours. The bottom layer seems unmodified. Macroscopic and microscopic cracks run through the intermediate layer (2–15 mm depth). The top layer has stiffened thanks to resolidification of copper. The temperature reaches 1000 °C during the braking test, which also explains the carbon diffusion into iron that result in the weakening of iron –graphite interfaces in the pad. Finally, submicronic particles are detected at many open interfaces of the worn and compressed pad. Associated with the predominant role of graphite particles, this explains the weak compressive behaviour of the pads. [ABSTRACT FROM AUTHOR]

During the excavation of underground projects, the rock masses left as the bearing support system are also subjected to dynamic loads from the excavation activities ahead. These rock masses have been damaged and fractured during the initial exposure (dynamic loads) and are subjected to static loads in the subsequent process as the support system. In this study, granite rock samples and specimens with different angles were produced, preloaded with different confining pressure, and under a combination of dynamic and static loading tests using a modified dynamic and static loading system: split Hopkinson pressure bar (SHPB). The peak strain and dynamic modulus of elasticity are weakened by the inclination angle in a similar way to the strength, with the specimens showing an evolutionary pattern from tensile strain to shear damage. The change in the inclination angle of flaws would weaken the dynamic and combined strengths, and a larger inclination flaw results in a significant decrease in its strength. Fractal analysis revealed that the fractural dimension was closely related to the fissure angle and showed a good linear correlation with the strain rate. This study will provide an important security assurance for deep mining. [ABSTRACT FROM AUTHOR]

Due to limitations of traditional measuring methods, a necessity of verification of applicability of optical measuring systems in different fields of science is required. The paper presents the application of a non-contact, non-destructive ARAMIS optical system in the analysis of static work of unstrengthened and strengthened laminated veneer lumber beams (LVL) with composite materials, subjected to a four-point bending test. The beams were strengthened with Carbon Fiber Reinforced Polymer (CFRP) sheets and laminates. The sheets were bonded to the external surfaces in three configurations differing in the number of layers applied and the degree of coverage of the side surface. The CFRP laminates were glued into predrilled grooves and applied to the underside of the beams. An adhesive based on epoxy resin was used. The scope of the work includes analysis of the strain distribution, stiffness and ductility. The analysis was performed on the basis of measurements made with an optical measurement system. The strain analysis indicated a change of the distribution of the strain in the compressive zone from linear for the unstrengthened to bilinear for the strengthened beams. The stiffness increase was equal from 14% up to 45% for the application of the CFRP laminates in the grooves and CFRP sheets bonded externally, respectively. Similar improvement was obtained for the ductility. [ABSTRACT FROM AUTHOR]

As a composite material, the stability of rock mass is usually controlled by a joint. During the process of excavation, the normal stress of the joint decreases continuously, and then the shear strength of the joint decreases, which may eventually lead to the instability and failure of rock mass. Previous studies have mainly focused on the shear behavior of joints under constant normal stress, but have rarely considered the unloading of normal stress. In this paper, a direct shear test of joints with different roughness was carried out, in which the shear stress remained unchanged while the normal stress decreased. The strength characteristics of joints were explored, and the deformation and acoustic emission-counting characteristics of joints were analyzed by digital image correlation (DIC) techniques and acoustic emission (AE). A new method for predicting the instability of joints under normal unloading was proposed based on the evolution law of normal deformation energy (Un), tangential deformation energy (Us) and total deformation energy (U0). The results show the following: (1) The unloading amount of normal stress was enlarged for greater initial normal stress and roughness, while it decreased with an increase in initial shear stress. (2) AE events reached their maximum when the normal stress was equal to the failure normal stress, and the b-value fluctuated more frequently in stable development periods under normal unloading conditions. (3) U0 would change with the loading and unloading of stress, and this may be used to predict the unloading instability of rock mass using the abrupt change of U0. [ABSTRACT FROM AUTHOR]

The research provides an innovative contribution to the interpretation of three-point and four-point bending tests on mortars by employing a bi-modulus material model, which assumes an asymmetric constitutive law, i.e., different elastic moduli in tension and in compression. To this aim, Euler–Bernoulli and Timoshenko bi-modulus beam models are defined, and the related displacement fields are reported for three-point loading, and provided for the first time for the four-point bending layout. A wide experimental campaign, including uni-axial tensile and compressive tests, three-point and four-point bending tests, and on notched specimens three-point tests for mode-I fracture energy, has been carried out on lime mortar specimens exploiting traditional contact (CE-DT) and contactless (DIC) measurement systems. Experimental results provided the values of tensile and compressive mechanical characteristics, which are employed to validate estimations of the analytical model. The tension-to-compression moduli ratio experimentally observed is on average 0.52. Experimental outcomes of the DIC analysis proved the bi-modulus behaviour during the four-point bending tests showing visible shifting of the neutral axis. The bi-modulus analytical model provides closer results to the experimental ones for the slender specimens subjected to four-point bending. [ABSTRACT FROM AUTHOR]

The paper presents the results of research on a composite mixture intended for use in road construction. The purpose of developing the mixture is to be able to use large amounts of industrial waste to produce building material. The waste used are coal slate from the mining industry, shredded rubber waste from used passenger car tires and fly ash from power plants. The mixture (SRFC) consists of unburnt coal-mining slate (S), shredded rubber waste (R), fly ash (F) and cement(C). A test under cyclic loading conditions was carried out on samples prepared from the SRFC mixture, in which the global deformations and local strains caused on the samples were measured. A measurement system using digital image correlation was used for the research. On the basis of the conducted research, it was found that the content of shredded rubber waste significantly influences the deformability of the tested mixtures and allows for the extension of the scope of elastic deformation in which the tested samples work. [ABSTRACT FROM AUTHOR]

Dual adhesives are mainly used to increase the strength of single lap joints (SLJs) by reducing the stress concentration at its ends. However, they can also be used to design the characteristics of the joint so that its operation and failure occur in several stages. This paper presents the results of uniaxial tensile tests for dual-adhesive and triple-adhesive SLJs. The adherends were made of aluminum and glass fiber-reinforced polymer (GFRP) composite. For dual-adhesive SLJs, 10 epoxies and 1.6 mm thick double-sided adhesive tape were used. The stiffest (Epidian 53 (100 g) + "PAC" hardener (80 g)) and most elastic (Scotch-Weld 2216 B/A Translucent) joints were determined, which were then used in a triple-adhesive joint with the same double-sided adhesive tape. Circular holes of different diameters from 8 mm to 20 mm were made in the double-sided adhesive tape, which were filled with liquid epoxy adhesive by injection after the adherends were joined. By using the double-sided adhesive tape, the geometry of the epoxy joints was perfect, free of spews, and had a constant thickness. The effect of the spot epoxy joint diameters and the arrangement of stiff and elastic joints in the SLJs were analyzed using digital image correlation (DIC). [ABSTRACT FROM AUTHOR]

To improve the flexural properties of cemented soils reinforced with fibers and avoid their brittle failure when subjected to complex loading conditions, a simple and cost-effective technique was explored to facilitate their application in retaining walls. In this study, how different fiber surface modifications, i.e., alkali treatment, acid treatment and silane coupling agent treatment, as well as different fiber contents, i.e., 0%, 0.25%, 0.5% and 1%, affect the bending properties of cemented soils was investigated by conducting three-point bending tests on notched beams. The digital image correlation (DIC) technology was used to examine the crack propagation process and the strain field distribution of cracks in specimens in the flexural tests. The results show that all fiber surface modifications increased peak strength and fracture energy, for example, the fracture energy of specimens AN1, AH1 and AK1 was increased by 180.4%, 121.5% and 155.4%, respectively, compared to PVA1. In addition, the crack tip strain, crack propagation rate and the initial crack width of the modified specimens were lower than those before modification. Lastly, scanning electron microscope (SEM) and mercury intrusion porosimetry tests were adopted to reveal the mechanism of bending performance in cemented soils reinforced by fiber surface modifications. [ABSTRACT FROM AUTHOR]

This work showcases a novel phenomenological method to create predictive simulations of metallic lattice structures. The samples were manufactured via laser powder bed fusion (LPBF). Simulating LPBF-manufactured metamaterials accurately presents a challenge. The printed geometry is different from the CAD geometry the lattice is based on. The reasons are intrinsic limitations of the printing process, which cause defects such as pores or rough surfaces. These differences result in material behavior that depends on the surface/volume ratio. To create predictive simulations, this work introduces an approach to setup a calibrated simulation based on a combination of experimental force data and local displacements obtained via global Digital Image Correlation (DIC). The displacement fields are measured via Finite Element based DIC and yield the true local deformation of the structure. By exploiting symmetries of the geometry, a simplified parametrized simulation model is created. The simulation is calibrated via Response Surface Methodology based on nodal displacements from FE-DIC combined with the experimental force/displacement data. This method is used to create a simulation of an anti-tetrachiral, auxetic structure. The transferability and accuracy are discussed, as well as the possible extension into 3D space. [ABSTRACT FROM AUTHOR]

The paper proposed an alternative optical metrology to classical methods (strain gauge measurements and numerical simulation) for strain determination on printed circuit board (PCBs) due to thermal loads. The digital image correlation (DIC) technique was employed to record the strain distribution in some particular areas of the PCB. A thermal load was applied using a heating chamber, and the measurements were performed at four different temperature steps (25 °C, 50 °C, 85 °C and 120 °C). An increase in the principal strains with temperature was observed. For validation, the principal strains on the PCB obtained with DIC were compared with the values from gauge strain measurements and numerical simulation. The conclusions highlighted that DIC represents a technique with potential for strain measurement caused by thermal deformation, with the advantages of full field measurement, less preparation of the surface and good accuracy. [ABSTRACT FROM AUTHOR]

In this study, the durability of cement-based repairs was observed, especially at the interface of debonding initiation and propagation between the substrate–overlay of thin-bonded cement-based material, using monotonic tests experimentally and numerically. Overlay or repair material (OM) is a cement-based mortar with the addition of metallic fibres (30 kg/m3) and rubber particles (30% as a replacement for sand), while the substrate is a plain mortar without any addition, known as control. Direct tension tests were conducted on OM in order to obtain the relationship between residual stress-crack openings (σ-w law). Similarly, tensile tests were conducted on the substrate–overlay interface to draw the relationship between residual stress and opening of the substrate–overlay interface. Three-point monotonic bending tests were performed on the composite beam of the substrate–overlay in order to observe the structural response of the repaired beam. The digital image correlation (DIC) method was utilized to examine the debonding propagation along the interface. Based on the different parameters obtained through the above-mentioned experiments, a three-point bending monotonic test was modelled through finite elements using a software package developed in France called CAST3M. Structural behaviour of repaired beams observed by experimental results and that analysed by numerical simulation are in coherence. It is concluded from the results that the hybrid use of fibres and rubber particles in repaired material provides a synergetic effect by improving its strain capacity, restricting crack openings by the transfer of stress from the crack. This enhances the durability of repair by controlling propagation of the interface debonding. [ABSTRACT FROM AUTHOR]

Car clutch facings are complex fiber-reinforced composites. The coefficient of thermal expansion (CTE) of the composite is one of the main thermal properties, which affects dry clutch engagement process due to heat associated with friction. In the case of clutch facing, which only exists in its final form as a non-planar annular disc, it is difficult to define an elementary representative volume. The objective of this work was to develop a method for identifying the CTE distributions on the entire part. A device allowing measuring the strain fields by digital image correlation (DIC) under homogeneous thermal loading (up to 300 °C) was developed. The experimental results highlight the heterogeneity and the orthotropic nature of the material behavior and the influence of the angle between the fibers on the CTE. To take into account that the measured strain fields are related to the CTE, but also to the shape of the part, different approaches to identify the CTE were considered: direct measurements, classical laminate theory (CLT) and finite element method updating (FEMU). Only the FEMU allows an accurate identification of the CTE distributions. Nevertheless, the CLT respects the orders of magnitude and remains a useful tool for the design of clutches. [ABSTRACT FROM AUTHOR]

A new technology was recently developed for municipal solid waste incineration (MSWI) fly ash stabilization, based on the employment of all waste and byproduct materials. In particular, the proposed method is based on the use of amorphous silica contained in rice husk ash (RHA), an agricultural byproduct material (COSMOS-RICE project). The obtained final inert can be applied in several applications to produce "green composites". In this work, for the first time, a process for pre-treatment of rice husk, before its use in the stabilization of heavy metals, based on the employment of Instant Pressure Drop technology (DIC) was tested. The aim of this work is to verify the influence of the pre-treatment on the efficiency on heavy metals stabilization in the COSMOS-RICE technology. DIC technique is based on a thermomechanical effect induced by an abrupt transition from high steam pressure to a vacuum, to produce changes in the material. Two different DIC pre-treatments were selected and thermal annealing at different temperatures were performed on rice husk. The resulting RHAs were employed to obtain COSMOS-RICE samples, and the stabilization procedure was tested on the MSWI fly ash. In the frame of this work, some thermal treatments were also realized in O2-limiting conditions, to test the effect of charcoal obtained from RHA on the stabilization procedure. The results of this work show that the application of DIC technology into existing treatment cycles of some waste materials should be investigated in more details to offer the possibility to stabilize and reuse waste. [ABSTRACT FROM AUTHOR]

Concretes with dispersed reinforcement are increasingly used in structural engineering. The basic source of knowledge on their application and design are the Model-Code 2010 guidelines. These guidelines, however, apply mainly to steel rebar reinforcement and are not fully sufficient in the analysis of the load-bearing capacity of elements made of concrete with dispersed reinforcement. Therefore, scientific research in this field is carried out continuously. The main goal of our work is to provide experimental data for the calibration of constitutive models of the cracking mechanics of concrete with reinforcement in the form of steel and polypropylene fibers. This article shows the possibility of using the digital image correlation system (DIC) to achieve this goal. The method of sample preparation and the method of conducting the tests were modeled on the recommendations contained in the PN-EN 14651: 2007 standard. The tests were carried out on prismatic elements with a notch loaded in a three-point bending setup. The results of standard strength tests are presented in the form of column graphs and tables. As an extension, the results of calculations of energy dissipated in fracture process are given. Moreover, the experimentally obtained graphs of the relationship between the force, displacement and crack opening were presented, which were supplemented with the images of crack development obtained with the use of DIC. The development of the crack net is characterized not only qualitatively but also quantitatively as a function of deflection or crack mouth opening displacement. Conclusions concerning the adopted research methodology and the tested materials are presented at the end of the article. [ABSTRACT FROM AUTHOR]

By optimizing the distribution of steel fibers in fiber-reinforced cementitious mortar (FRCM) through the layered structure, the role of fibers can be fully utilized, thus improving the flexural behavior. In this study, the flexural behavior of layered FRCM at different thicknesses (25 mm, 50 mm, 75 mm, 100 mm) of the steel fiber layer was investigated. The evolution of the crack propagation behavior was analyzed using the digital image correlation (DIC) technique. The results showed that the steel fiber layer thickness of 75 mm has the best flexural behavior. Moreover, the crack propagation path is more tortuous. The maximum value of crack opening displacement (COM) increases with the increase in fiber thickness. In addition, increasing the bottom layer thickness can increase the height of the tensile zone, but the interface inhibits the increase of the tensile zone. [ABSTRACT FROM AUTHOR]

This paper presents new methodology for determining the actual stress–strain diagram based on analytical equations, in combination with numerical and experimental data. The first step was to use the 3D digital image correlation (DIC) to estimate true stress–strain diagram by replacing common analytical expression for contraction with measured values. Next step was to estimate the stress concentration by using a new methodology, based on recently introduced analytical expressions and numerical verification by the finite element method (FEM), to obtain actual stress–strain diagrams, as named in this paper. The essence of new methodology is to introduce stress concentration factor into the procedure of actual stress evaluation. New methodology is then applied to determine actual stress–strain diagrams for two undermatched welded joints with different rectangular cross-section and groove shapes, made of martensitic steels X10 CrMoVNb 9-1 and Armox 500T. Results indicated that new methodology is a general one, since it is not dependent on welded joint material and geometry. [ABSTRACT FROM AUTHOR]

Two-dimensional meso-scale finite element models with real aggregates are developed using images obtained by digital image processing to simulate crack propagation processes in concrete under uniaxial compression loading. The finite element model is regarded as a three-phase composite material composed of aggregate, mortar matrix and interface transition zone (ITZ). Cohesive elements with traction–separation laws are used to simulate complex nonlinear fracture. During the experiment, digital image correlation (DIC) was used to obtain the deformation and cracks of the specimens at different loading stages. The concept of strain ratio is proposed to describe the effectiveness of simulation. Results show that the numerical strain ratio curve and stress–strain curves are both in good agreement with experimental data. The consistency between the cracks obtained by simulation and those obtained by DIC shows the good performance of cohesive elements as well as the effectiveness of simulation. In summary, the model is able to provide accurate predictions of the whole fracture process in concrete under uniaxial compression loading. [ABSTRACT FROM AUTHOR]

Dissimilar metal weld joints of Monel 400 and Stainless Steel 316L stainless steel were carried out using Gas Tungsten Arc Welding (GTAW). Conventional annealing and cryogenic treatment were performed on the welded joints. Weld joints of this combination of materials have enormous potential applications in power industry and the available related literature is limited. In the present study, the tensile properties of heat treated (HT), cryotreated (CT), and untreated (UT) specimens were studied. The engineering stress and strain were determined experimentally as per Standard Test Methods for Tension Testing of Metallic Materials (ASTM E8). The strain distribution was evaluated at different zones of weld joint was evaluated using Digital Image Correlation (DIC). Significant difference was noticed between the zones. Weld zone of all samples had less local stress and strain and SS 316L heat affected zone (HAZ) zone had more local stress and strain when compared to other zones. The local strain distribution along distance from weld center line and local stress-strain curves of different zones are also predicted. Scanning Electron Microscopy was used to analyze the fracture behavior of welded samples for HT, CT, and UT specimens. [ABSTRACT FROM AUTHOR]

Cervical spine injuries (CSIs) arising from collisions are uncommon in contact sports, such as rugby union, but their consequences can be devastating. Several FE modelling approaches are available in the literature, but a fully calibrated and validated FE modelling framework for cervical spines under compressive dynamic-impact loading is still lacking and material properties are not adequately calibrated for such events. This study aimed to develop and validate a methodology for specimen-specific FE modelling of vertebral bodies under impact loading. Thirty-five (n = 35) individual vertebral bodies (VBs) were dissected from porcine spine segments, potted in bone cement and μ CT scanned. A speckle pattern was applied to the anterior faces of the bones to allow digital image correlation (DIC), which monitored the surface displacements. Twenty-seven (n = 27) VBs were quasi-statically compressively tested to a load up to 10 kN from the cranial side. Specimen-specific FE models were developed for fourteen (n = 14) of the samples in this group. The material properties were optimised based on the experimental load-displacement data using a specimen-specific factor ( k G S s t a t i c ) to calibrate a density to Young's modulus relationship. The average calibration factor arising from this group was calculated ( K ¯ G S s t a t i c ) and applied to a control group of thirteen (n = 13) samples. The resulting VB stiffnesses was compared to experimental findings. The final eight (n = 8) VBs were subjected to an impact load applied via a falling mass of 7.4 k g at a velocity of 3.1 m s −1. Surface displacements and strains were acquired from the anterior VB surface via DIC, and the impact load was monitored with two load cells. Specimen-specific FE models were created for this dynamic group and material properties were assigned again based on the density–Young's modulus relationship previously validated for static experiments, supplemented with an additional factor ( K G S d y n a m i c ). The optimised conversion factor for quasi-static loading, K ¯ G S s t a t i c , had an average of 0.033. Using this factor, the validation models presented an average numerical stiffness value 3.72 % greater than the experimental one. From the dynamic loading experiments, the value for K G S d y n a m i c was found to be 0.14, 4.2 times greater than K ¯ G S s t a t i c . The average numerical stiffness was 2.3 % greater than in the experiments. Almost all models presented similar stiffness variations and regions of maximum displacement to those observed via DIC. The developed FE modelling methodology allowed the creation of models which predicted both static and dynamic behaviour of VBs. Deformation patterns on the VB surfaces were acquired from the FE models and compared to DIC data, achieving high agreement. This methodology is now validated to be fully applied to create whole cervical spine models to simulate axial impact scenarios replicating rugby collision events. [ABSTRACT FROM AUTHOR]

The size of the fracture process zone (FPZ) has significance for studying the fracture mechanism and fracture characteristics of concrete. This paper presents the method of assessing the FPZ of Mixed-Mode I-II for quasi-static four-point shearing concrete beams with pre-notched by Lagrangian strain profiles from digital image correlation (DIC). Additionally, it explores the influences of volume rates of the coarse aggregate of 0%, 28%, 48%, and 68%, and the specific surface areas of 0.12 m2/kg, 0.15 m2/kg, and 0.26 m2/kg on the size of the FPZ. It shows that the size of FPZ in four-point shearing concrete beam can be characterized by the displacement field and strain field using DIC. The size of FPZ conforms to linear positive correlation with the volume rate of coarse aggregate, and linear negative correlation with the specific surface area of coarse aggregate. It presents that the crack initiation of the four-point shearing beam with the pre notch is dominated by mode I load, and the propagation and fracture of Mixed-Mode I-II cracks are caused by the combined effect of Mode I and Mode II loading. [ABSTRACT FROM AUTHOR]

The research hypothesis states that the impregnation of the honeycomb paper core of lightweight sandwich panels with modified starch, sodium silicate and epoxy resin (LiquidWood®) resin has a significant effect on its elastic properties. In this study, a recycled paper was used in three thicknesses, seven types of cell shapes, including two after numerical optimization and three types of impregnating agents. The method of digital image analysis determined the elastic constants of manufactured paper cores, which were subjected to axial compression in two directions. Based on the experimental results, elastic constants of the cores were calculated and compared with the results of numerical calculations. It has been shown that each of the impregnating solutions used improved the stiffness of the paper core. The best results were obtained for LiquidWood® epoxy resin and modified starch. An important parameter of cell geometry affecting their rigidity is the angle of the cell wall φ, as well as the arrangement of the common cell wall in relation to the direction of load. The numerical models developed were positively verified. [ABSTRACT FROM AUTHOR]

The crack propagation and failure of 3D-printed samples with prefabricated K–S fissures (a kinked fissure and a straight fissure) were observed under uniaxial compression, and the strain and displacement of the sample surface were quantified by the digital image correlation (DIC) method. The experimental results show that the branch inclination angle of the kinked fissure is an important factor affecting the crack initial position, and the evolution of the strain field during the failure process of the sample can better reflect the cracking law of the internal fissures. Furthermore, two coalescence modes are classified: Mode I is a tension–shear composite failure formed by the penetration of the tension–shear composite crack; Mode II is a tensile failure that penetrates the whole samples during the failure process without rock bridge damage. In addition, the numerical simulation results were well consistent with the cracking and failure modes. [ABSTRACT FROM AUTHOR]