Crack Pattern Evolution Research Articles

Deciphering the Benefits of Coordinated Binders in Si‐Based Anodes by Combined Operando/In Situ and Ex Situ X‐Ray Micro‐ and Nano‐Tomographies

AbstractThe simple addition of a Zn(II) precursor to a preoptimized poly(carboxylic acid) binder solution enhances the electrochemical performance and cycle life of silicon‐based electrodes. The binder/cation couple forms a cross‐linked coordinated binder that plays a key role in enhancing the mechanical and chemical stability of the electrode microstructure. The impact of the addition of the Zn precursor on the microstructural evolution of the electrode during cycling is investigated at different scales (from cell/electrode to silicon particle scale) using complementary operando, in situ, and ex situ X‐ray tomography techniques. Comparative analyses conducted on the reference and with Zn electrode formulations using operando and in situ X‐ray micro‐tomography allow for monitoring of the electrode morphological deformations along with the crack pattern formation and evolution during cycling. The benefits of the precursor addition include enhancing the mechanical stability of the electrode through a strengthened microstructure more apt to maintaining its integrity, as well as a better anchoring to the current collector leading to decreased electrical disconnections and capacity fade. Moreover, complementary ex situ X‐ray nano‐tomography measurements highlight the benefits of the precursor addition in terms of chemical stability with mitigated solid electrolyte interface (SEI) formation over the electrode cycling.

Experimental investigation of the compressive and shear resistance of laminated steel-reinforced glass beams

This paper presents an experimental investigation into the compressive and shear resistance of triple-layered laminated steel-reinforced glass beams. Two types of tests are performed: (a) local compressive tests (force over a support) and (b) bending tests (force close to a support). In total, six local compressive tests and eight bending tests are performed. Overall, beams with a shear span-to-effective depth ratio (a/d) approximately equal to 0, 0.63, and 1.0 are tested. Two different types of flexural reinforcement are used separately: solid (S) and hollow (H) reinforcement. The behaviour of the outer glass panes, and top and bottom reinforcement is monitored using strain gauges and Digital Image Correlation (DIC). The test results are elaborated in terms of load-displacement curves, the evolution of strains and crack patterns. Three failure modes are observed: yielding of the reinforcement (PF), crushing of glass (CF), and rupture of the reinforcement (RR). Shear failure occurred due to the crushing of glass in the compressed diagonal strut in the shear span. It was found that the shear resistance increases with a smaller shear span-to-effective depth ratio and stronger reinforcement. The dominant shear transfer mechanism was the direct strut action. It was found that the post-fracture capacity had a relatively constant value for all the tests with a slight increase for smaller a/d. The actual tensile strains in the bottom reinforcement measured by DIC are compared with the calculated strains based on the curvature of uncracked and cracked cross-sections, assuming plane section behaviour. It was observed that the actual strains are systematically larger than the calculated ones because, in reality, the section does not remain plane. After the appearance of the first crack, the beams essentially behave like strut-and-tie systems, where the strut is the diagonally compressed laminated glass and the tie is the bottom reinforcement.

CRACKING PATTERN ANALYSIS OF THE TURNING BAND METHOD (TBM) APPLICATION ON A SINGLE-REINFORCEMENT BAR CONCRETE BEAM MODELLING USING THE MAZARS DAMAGE

The development of crack patterns in reinforced concrete structures is a randomly stochastic process influenced by the heterogeneous nature of concrete materials, which impacts the sensitivity to damage and variability in mechanical properties. The numerical simulation of damage pattern appearance on the reinforced concrete for special building structures needs a realistic result, especially in terms of crack distribution. The Turning Band Method (TBM) serves as a tool for assessing the variability of concrete heterogeneity, functioning as an operator to generate a random variable for each specific field. In this study, the investigation of crack patterns in reinforced concrete structures involves using a simple concrete beam sample, measuring 10x10x50 cm3, with a single longitudinal reinforcement cast in the centre. This beam is subjected to an axial tensile loading, while the Mazar Damage Model is employed as the concrete behaviour law. Through the implementation of The Turning Band Method (TBM) and the variation of the random field parameters, distinct crack patterns are observed, not only the number but also the locations of cracks. The use of a smaller correlation length showed 2 cracks while the larger size had around 1 to 3 cracks, with the first crack localizations of each sample generally occurring in the middle surface, in which a noticeable contrast to non-TBM modelling just displays 1 crack. Furthermore, the resulting probability of cracks for ten random draws demonstrates similarity to experimental tests and numerical simulation of the previous study, both at global and local levels.

Behavior and shear strength of prestressed steel reinforced concrete composite deep beam

In order to optimise the utilisation of material properties, simplify the construction process and enhance the industrialisation of steel reinforced concrete beams, an innovative prestressed steel reinforced concrete composite beams(PSRCC) was proposed, which was achieved by integrating prestressing technology and prefabricated technology to steel reinforced concrete structure. To investigate the shear PSRCC deep beams, a static load test was conducted on 7 PSRCC deep beams. The study investigated the effects of parameters such as shear span-depth ratio, prestressed tendons degree, form, height and application sequence on the failure mode, crack pattern, load-displacement behavior, strain response and damage evolution. A model was established to predict the shear strength of PSRCC deep beams, considering the steel-concrete interaction, using the von Mises yield criterion and the SST model, which assessed the contributions of composite strut, prestressed tendons and shear steel web for shear strength. The test results showed that the prefabricated and cast-in-situ concrete components maintained good integrity, and PSRCC deep beams eventually experienced typical diagonal compression failure. Applying prestressing and reducing the shear span-depth ratio under identical conditions would reduce the deformation capacity of PSRCC deep beams. When the shear span-depth ratio was reduced from 1.0 to 0.5, the cracking load and peak load of the specimens increased by 17.31 % and 16.53 % respectively. Increasing the prestress level from 0 to 0.3 and 0.6 increased the cracking load of the specimens by 1.41 and 2.36 times, respectively, but the peak load of the specimens increased by only 3.37 % and 8.17 %. The cracking load of the parabolic tendon specimen increased by 2.18 for the comparison specimen but was 8.33 % lower than that of the linear tendon specimen with the same degree of prestressing. Comparison of the two prestressing sequences showed that the cracking load of the specimen with tensioning prestressed tendons after pouring the entire beam section increased by 29.84 %, but the peak load increased by only 3.11 %. As the height of the prestres tendons increased, the cracking and peak loads of the specimen reduced by 5.84 % and 5.71 % respectively. Consequently, the shear strength of PSRCC deep beams was significantly influenced by the shear span-depth ratio and minimally affected by prestress-related parameters. The proposed model accurately predicted the shear strength of PSRCC deep beams compared to existing codes, offering valuable guidance for design.

Experimental study on mechanical behavior of precast large-cantilevered UHPC bent caps with π-shaped cross-sections

To reduce the self-weight of the precast bent caps with large cantilevers commonly used in municipal bridge construction, an innovative thin-walled bent cap scheme made of ultra-high-performance concrete (UHPC) was proposed in this paper. Six scaled bent cap specimens, characterized by a scale ratio of 1:2.5, were subjected to static loading tests, encompassing both bending-shear and bending-shear-torsion combinations. Throughout the loading process, careful observations were made regarding the progressive development of crack patterns, stress distribution within various materials, and the identification of ultimate failure modes. It was observed that for the UHPC cap beams with small shear span-to-depth ratios, both the web shear cracks and flexural cracks were fully developed, leading to a combined shear and bending failure mode. With shear span-to-depth ratio increased, the effect of bending behavior became more and more dominate, resulting in an increased ductility. When subjected to a combined bending-shear-torsion loading, the UHPC bent caps exhibited conspicuous diagonal shear failure attributes, indicating that the torsion presented in the bent caps should be limited. In summary, the adoption of a π-shaped section for the UHPC bent caps with large cantilevers results in an impressive weight reduction of 40%∼50% compared to the conventional solid cap beam design. Moreover, the proposed design not only aligns with specifications in terms of cracking strength and ultimate bearing capacity but also facilitates monolithic precast, making it exceptionally well-suited for practical engineering applications.

Biaxial behaviour of concrete and its failure mechanics under quasi-static and dynamic loading: A numerical study

In the present study, the biaxial behaviour of concrete and its mechanics under quasi-static and dynamic loading conditions are analysed using the meso-model of concrete. A three-phase cubic meso-model is developed, which consists of mortar, interfacial transition zone, and aggregate. A finite element split Hopkinson pressure bar is developed for the biaxial dynamic loading. The mechanics of the crack pattern development in concrete under uniaxial and biaxial loading are investigated. The failure process and its mechanics for each loading condition are also explained in four steps. Similar cracks are obtained for the quasi-static and dynamic biaxial loading; however, the cause of failure is found to be contrasting.

Fracture morphology of desiccation cracks in clayey soil

Desiccation cracks compromise soil integrity and weaken its strength, causing a range of detrimental consequences across various domains. Elucidating the cracking mechanism can aid in managing crack propagation and mitigating the associated risks. This study monitored and compared the evolution of crack patterns on the soil surface and fracture morphologies on the soil cross-section during the drying process using a tested soil sample. Multiple fracture morphological features are discerned on the soil cross-section, encompassing initiation points and plumose structures. Soil fracture morphologies are categorized into three cases based on the initiation point's location, referred to as “Top-initiated structure”, “Bottom-initiated structure”, and “Truncated structure”. Experimental results demonstrate that plumose structures result from the division of the crack front under mixed-mode loading. Cracking under mixed-mode I + II loading leads to cross-section tilting, resulting in curved surface cracks. Conversely, cracking under mixed-mode I + III loading causes cross-section twisting, generating hackle lines and step structures. Furthermore, the crack front radiates from the initiation point, creating orthogonal hackle lines. The geometric relationship confirms that the soil fracture morphology is a good indicator of the cracking process, both in laboratory tests and field observations.

Evolution of polygonal crack patterns in mud when subjected to repeated wetting–drying cycles

The present paper demonstrates how a natural crack mosaic resembling a random tessellation evolves with repeated ‘wetting followed by drying’ cycles. The natural system here is a crack network in a drying colloidal material, for example, a layer of mud. A spring network model is used to simulate consecutive wetting and drying cycles in mud layers until the crack mosaic matures. The simulated results compare favourably with reported experimental findings. The evolution of these crack mosaics has been mapped as a trajectory of a 4-vector tuple in a geometry-topology domain. A phenomenological relation between energy and crack geometry as functions of time cycles is proposed based on principles of crack mechanics. We follow the crack pattern evolution to find that the pattern veers towards a Voronoi mosaic in order to minimize the system energy. Some examples of static crack mosaics in nature have also been explored to verify if nature prefers Voronoi patterns. In this context, the authors define new geometric measures of Voronoi-ness of crack mosaics to quantify how close a tessellation is to a Voronoi tessellation, or even, to a Centroidal Voronoi tessellation.

The influence of density on the fracture energy of AAC: From experimental investigation to the calibration of a cohesive law

The paper investigates cracking development in Autoclaved Aerated Concrete (AAC) elements, and clarifies the effect of density and porosity on material mechanical properties. To this purpose, 4 material densities are analyzed, ranging from 300 kg/m3 to 580 kg/m3, corresponding to a compressive strength interval approximately ranging from 1.90 MPa to 5.50 MPa. Fracture mechanics of AAC is analyzed by carrying out three-point bending tests on notched beams, similar to those commonly used for normal concrete elements. In these tests, the onset and development of crack pattern is studied by means of Digital Image Correlation technique. An almost linear dependence of fracture energy from density (and consequently from strength) is derived based on test results. Experimental results are used to calibrate a bi-linear cohesive law, whose parameters vary with material density, so allowing to differentiate fracture properties for structural (high density) and non-structural (low density) AAC elements in finite element analyses. The cohesive law parameters are calibrated by exploiting a neural network algorithm and interfacing MatLab with ABAQUS Finite Element package. The curves obtained for the 4 investigated densities, normalized with respect to material tensile strength, are almost superimposed on each other as if the stresses were scaled with porosity. The displacements corresponding to the knee of the curve are nearly coincident, independently from material density. The good agreement between experimental and numerical results proves the reliability of the proposed approach.

Ultra-thin Strain Hardening Cementitious Composite (SHCC) layer in reinforced concrete cover zone for crack width control

In the current study, experiments and numerical simulations were carried out to investigate the cracking behavior of reinforced concrete beams consisting of a very thin layer (i.e., 1 cm in thickness) of SHCC in the concrete cover, tension zone. A novel type of SHCC/concrete interface that features a weakened chemical adhesion but an enhanced mechanical interlock bonding was developed to facilitate the activation of SHCC. The study involved testing hybrid SHCC/concrete beams that have various types of interfaces. The results were compared to the control reinforced concrete beams that do not have SHCC in the cover. Four-point bending tests were performed with the beams and Digital Image Correlation (DIC) was utilized to track the development of crack pattern and crack width. Results show that hybrid beams possessed similar load bearing capacity but exhibited a significantly improved cracking behavior as compared to the control beam. With a 1-cm-thick layer of SHCC, the maximum crack width of the best performing hybrid beam exceeded 0.3 mm at 53.3 kN load, whereas in the control beam the largest crack exceeded 0.3 mm at 32.5 kN load. The hybrid beam with the proposed new interface formed 10 times more cracks in SHCC than the hybrid beam with a simple smooth interface and had an average crack width less than 0.1 mm throughout the loading. The lattice model has successfully showcased its ability to predict and offer valuable insights into the fracture behavior of hybrid systems. The simulation results indicate that the presence of a weak interface bond, coupled with mechanical interlocking, can effectively facilitate the activation of SHCC, resulting in the formation of more cracks and a delayed progression towards the maximum crack width. As the volume ratio of SHCC used in the hybrid beams is only 6%, the current study highlights the strategic use of minimum amount of SHCC in the critical region to efficiently enhance the performance of hybrid structures.

Calibration of phase-field brittle fatigue model by purposeful design of crack driving forces

A new general multiparameter phase-field approach for high-cycle fatigue fracture is proposed. Fatigue is modelled by adding a new energy dissipation term accounting for fatigue phenomena, which results in two additional crack driving forces. The current model analysed in the paper possesses four fatigue parameters, whereby each of the driving forces depends on two parameters. The crack driving forces are designed so as to enable a more accurate reproduction of S-N curves and the Paris’ law by a single set of identified parameters, which is not possible by simpler phase-field models relying on only one or two fatigue parameters. The results indicate that the presented model is able to capture various macroscopic phenomena, including the mean stress effect, the evolution of complex crack patterns under cyclic loading and the reproduction of experimental S-N and Paris curves of realistic materials. Extensive parametric analyses have revealed that there exists a strong correlation between the model fatigue parameters and the parameters defining S-N and Paris’ curves, which opens the possibility of straightforward calibration of each parameter from experimental data.

Desiccation cracking behaviour of a vegetated soil incorporating planting density

Vegetation has been widely used in geotechnical engineering. However, desiccation cracking in vegetated soils is very common and often neglected. This study aims to investigate desiccation cracking behaviour of a vegetated soil considering different planting densities. The evolution of water content and surface crack pattern during drying is monitored. Experimental results show that during the early stage of drying, the evapotranspiration rate of the vegetated sample with a smaller planting density is slightly less than the evaporation rate of the bare soil sample, and the evapotranspiration rate increases with increasing planting density. In the vegetated samples, cracks initiate almost simultaneously. The larger the planting density, the more the crack initiation points and the smaller the cracking water content. In terms of the final crack pattern, both the surface crack ratio and the average crack width of vegetated samples are smaller than those of the bare sample. As the planting density increases, there are more fine and thin cracks. However, increasing planting density does not lead to a continuous decrease in cracking degree. It is necessary to select an appropriate planting density (about 24 g/m2 in this study) to maximize the inhibitory effect of vegetation on soil desiccation cracking.

Study on the behavior of Z-A composite under fiber laser processing in different environments

Fiber laser, as a unique tool, has proven its supremacy in processing implant materials. Being a thermal-based tool, it has some ineptitude against surface functionality, like the development of crack patterns, which is a severe issue that endangers the longevity of orthopedic implants. The medical world has paid close attention to this problem in recent years. In this context, the current study investigates the impact of laser fluence on the crack behavior during the ablation of Z-A (zirconia-alumina) composite under dual environments like ambient air and water. According to the current research’s findings, it has been observed that the Z-A composite acts differently in different environments under the same thermic load. The adverse impact of laser fluence seems to be meager, while Z-A is processed in a wet environment compared to a dry one. As a result, considerable residual stresses support forming of a network of cracks in a dry environment. However, no cracks were seen in the wet medium due to low stress and prolonged fracture toughness. Furthermore, with the support of characterization tools, the crack mechanism under ambient air and water environments is addressed. The findings of this study are expected to minimize the crack growth and the challenges associated with fiber laser-processed surfaces to make it an ideal implant viable for wider clinical adoption.[copyright information to be updated in production process]

Healing behaviour of desiccation cracks in a clayey soil subjected to different wetting rates

Desiccation cracks initiate and propagate during the drying process and healing occurs during the wetting process. However, most of the previous studies only paid attention to the drying-induced crack propagation and the wetting-induced healing behaviour was always neglected. In this paper, a series of wetting tests were conducted on cracked soils under different wetting rates. The crack pattern evolution during wetting was recorded and quantitatively analysed. The results show that the narrow and short secondary and tertiary cracks heal earlier than the long and wide primary cracks during wetting. With the elapsed wetting time, the surface crack ratio and average crack width decrease slowly at first, then rapidly decrease and eventually stabilise. However, at the early stage of wetting, the total crack length almost remains constant. The healing of desiccation cracks in clayey soils is mainly attributed by two factors: wetting-induced swelling and disintegration. Furthermore, the healing degree of desiccation cracks become higher with increasing wetting rate. The healing of desiccation cracks with a lower wetting rate is mainly due to the wetting-induced swelling of soils. However, that with a higher wetting rate is dominated by both swelling and disintegration.

Understanding resistance increase in composite inks under monotonic and cyclic stretching

Cyclic degradation in flexible electronic inks remains a key challenge while their deployment in life critical applications is ongoing. The origin of electrical degradation of a screen-printed stretchable conductive ink with silver flakes embedded in a polyurethane binder is investigated under uniaxial monotonic and cyclic stretching, using in-situ confocal microscopy and scanning electron microscopy experiments, for varying ink thickness (1, 2, and 3 layers, each layer around 8–10 μm) and trace width (0.5, 1, and 2 mm). Cracks form under monotonic stretching, and the evolution of crack pattern (density, length and width) with applied strain is affected by ink thickness such that the 3-layer ink exhibits larger normalized resistance but slightly lower resistance than the 1-layer ink up to strains of 125%. For cyclic stretching, the crack density and length do not evolve with cycling. However, the cracks widen and deepen, leading to an increase in resistance with cycling. There exists a strong correlation between fatigue life, i.e. the number of cycles until a normalized resistance of 100 is reached, and the strain amplitude. The normalized resistance increase rate with respect to cycling is also found to scale with strain amplitude. The rate of change in resistance with cycling decreases with ink thickness and trace width. For practical applications, thicker (25 μm) and wider (⩾2 mm) inks should be used to lower resistance increases with repeated deformation.

Detecting Damage Evolution of Masonry Structures through Computer-Vision-Based Monitoring Methods

Detecting the onset of structural damage and its progressive evolution is crucial for the assessment and maintenance of the built environment. This paper describes the application of a computer-vision-based methodology for structural health monitoring to a shake table investigation. Three rubble stone masonry walls, one unreinforced and two reinforced, were tested under natural earthquake base inputs, progressively scaled up to collapse. White noise signals were also applied for dynamic identification purposes. Throughout the experiments, videos were recorded, under both white noise excitation and environmental vibrations, with the table at rest. The videos were preprocessed with motion magnification algorithms and analyzed through a principal component analysis. The natural frequencies of the walls were detected and their progressive decay was associated with damage accumulation. Results agreed with those obtained from another measurement system available in the laboratory and were consistent with the crack pattern development surveyed during the tests. The proposed approach proved useful to derive information on the progressive deterioration of the structural properties, showing the feasibility of this methodology for real field applications.

The Use of Artificial Intelligence for Image Processing of Crack Patterns in Panel Painting

In today world the image processing tools serve as a tool to study the various aspects of an image. In this study the purpose is to study the crack patterns in panel painting. First the cracks are extracted from a painting. Then it simplified with a line and a system of lines and the points of cross overs are studied as a model of crack pattern in that painting. Finally, the type of each cross points (X, Y or O), statics of line lengths and orientation, and crack island area are reported. The artificial intelligence is used for estimation of evolution of crack pattern is done based on continuation of end points and separating the big island to the smaller in load direction.

Cracking Patterns of Brittle Hemispherical Domes: an Experimental Study

Crack formation in hemispherical domes is a distinguished problem in structural mechanics. The safety of cracked domes has a long track record; the evolution of the cracking pattern received less attention. Here, we report displacement-controlled loading tests of brittle hemispherical dome specimens, including the evolution of the meridional cracking pattern. The 27 investigated specimens, 20 cm in diameter, were prepared in 3D printed molds, and their material is one of the three mixtures of gypsum and cement. We find that neither the (limited) tensile strength nor the exact value of the thickness significantly affects the statistical description of the cracking pattern, i.e., the cracking phenomenon is robust. The maximal number of the meridional cracks never exceeds seven before the fragments’ disintegration (collapse). We find that the size distribution of the fragments exhibits a lognormal distribution. The evolution is reflected in the load-displacement diagrams recorded in the test, too, as significant drops in the force are accompanied by an emergence of one or more new cracks, reflecting the brittle nature of the phenomenon. A simple, stochastic fragmentation model, in which a segment is fragmented at either in the middle or at the fourth point, fairly recovers the observed size distribution.

A numerical study of pitting corrosion in reinforced concrete structures

In RC structures, rebar corrosion causes the cracking of the concrete cover and the deterioration of the bond between the two materials. In this paper, a numerical model is developed to investigate these two phenomena. The corrosion pit is modeled as a radial displacement representing the volume expansion of the rebar. A concrete damage plasticity model is used to simulate the damaging of the cover and a particular care is given to finely model the concrete-rebar interface using a normal and tangential contact law. The numerical results obtained in our work are validated with experimental and analytical results from the literature. The first main conclusion of our work is that the pit size impacts highly the cracks paths and influences the length of the tensile cracks in the concrete. The second main result consists in showing and exploring the relation between the accumulation of the rust in the corrosion pit and the deterioration of the bond between the rebar and the concrete cover. • A 2D finite element model of pitting corrosion of a reinforced concrete beam is developed. • The evolution of the corrosion pit and volume expansion of the rebar is studied. • The evolution of crack patterns and crack length in accordance with the corrosion level is investigated. • The deterioration of the bond strength is studied and linked to the damaging of the concrete cover.

The use of X-ray microtomography to investigate the shear behavior of hybrid fiber reinforced strain hardening cementitious composites

This paper presents an experimental investigation on the shear response of strain-hardening cement-based composites (SHCC) using X-Ray microtomography (microCT). For the developed composites, PVA and micro steel fibers were used in a constant fiber volume fraction of 2.0 %. The hybrid composites were produced replacing PVA by steel fibers in 25 %, 50 % and 75 % fractions. The shear behavior of the composites was studied by performing Iosipescu shear tests. The crack pattern evolution along the tests and the displacement field in the notch region were analyzed using the Digital Image Correlation (DIC) technique. Information about the porosity, fiber distribution and alignment were obtained using microCT for each specimen tested . The results show that the hybridization increases the crack opening but has little effect on the shear strength. The results also show that PVA fibers affect the alignment of the steel fibers and increase the porosity of the composites. • PVA fibers increase the porosity and affect the alignment of steel fibers. • The inclusion of steel fibers increases the crack opening. • Steel fibers tend to concentrate in the notch region. • The largest pores do not affect the cracks pattern in the notch region.