Parametric study on the effect of anchor’s geometry on the stress distribution and crack initiation direction in a concrete body

This work deals with investigations of the stress field distribution around a steel anchor embedded in a concrete. Tensile loading - pulling force of the steel anchor is considered, which is very often connected to concrete cone failure. Numerical simulations via finite element method were performed to obtain results for a large extent of geometrical configurations. In accordance with the basic idea of the maximum tangential stress criterion, the angle where this stress reaches its maximum was determined. The influence of selected geometrical parameters of the system on these angles was analyzed and it was found out that they can significantly affect the angle of the maximum tangential stress and consequently the shape of the cone failure. It was observed that the circumferential crack propagation is flatter with increasing length of the steel anchor’s embedment and with increasing anchor’s outer radius. The results obtained numerically agree sufficiently with experimental results especially when the crack direction is compared. Conclusions presented within this research are important for both design and assessment of anchor/concrete systems subjected to tensile loading

Experimental and Computational Study on the Tensile and Flexural Properties of Polylactic Acid filled with Boron Nitride Nanoplatelets

Our research described in this paper focused on fabricating and characterising polylactic acid (PLA) composites reinforced with randomly dispersed boron nitride nanoplatelets (BNNP). The integrated experimental analysis with the Finite Element Method (FEM) computational simulation employed a multiscale modelling approach used to evaluate the effects of BNNP fillers at varying weight fractions (i.e. 0.005% to 0.04%). The simulations utilised Representative Volume Elements (RVEs) with 1 x 1 x 1 μm dimensions, incorporating randomly dispersed BNNP to mimic the realistic composite behaviour. The modulus predicted through the RVE approach was validated against empirical studies and pre-existing micromechanical models to ensure accuracy and reliability. The empirical findings revealed significant enhancements in the modulus of elasticity, tensile strength and flexural strength of the PLA reinforced with BNNP composites exhibiting improvements of 17.43%, 40% and 61% respectively at elevated filler concentrations of 0.005, 0.01,0.02,0.03 and 0.04. The Scanning Electron Microscopy (SEM) analysis of the fracture surfaces indicated a transition from ductile to brittle fracture patterns as the BNNP content increased, underscoring the reinforcing effect of the nanoplatelets. Flexural testing further validated improvements in the material rigidity and resistance to bending. The Finite element analysis (FEA) simulations strongly correlated with the experimental data, with deviations remaining within an acceptable range. This integrated approach underscores the efficacy of BNNP fillers in enhancing the mechanical attributes of PLA, yielding significant perspectives for developing eco-friendly composite materials exhibiting superior performance features

The assessment of the severity of local impact on a pro-bionic composite lattice shell by the use of fiber-optic sensors

The paper considers a pro-bionic lattice shell (PBLS) for civil aviation structures and the problem of getting the parameters of a local low-velocity impact taking the value of residual strain by fiber optic sensors (FOS) installed in PBLS. There was developed a numerical model of an equivalent smooth shell with a detailed part as an impact zone.  This detailed part have been constructed from a load-bearing rib containing layers of UD composite, matrix polymer, a protective tab and a skin. The matrix polymer layers and the protective tab had elastic-plastic properties, in the developed numerical model. The UD composite layers and the skin were orthotropic elastic media. FEM calculations showed that the location of FOS directly on the rib surface does not provide the required accuracy of getting impact residual strain. However, FOS installation into elastic-plastic protective tab makes solving the problem. Localized Bragg grating sensors must be installed into the FOS with a high density (every 1-2 cm along the rib) to indicate the impact location, which is technically difficult to implement. Distributed sensors (Brillouin scattering) have an advantage, allowing both to indicate the impact location by residual strain recording and to get possibility calculate later the most important parameter - the impact energy

Size Effect in Concrete Beams: A Numerical Investigation Based on the Size Effect Law

The size effect significantly influences the structural design of concrete elements, particularly when applying fracture mechanics principles. As structural dimensions increase, a significant outcome of the size effect is the decline in both strength and ductility. To characterize concrete fracture behavior, various fracture mechanics models have been proposed, integrating material fracture properties that are unaffected by changes in geometry and size. Bažant’s size effect law explains this phenomenon based on the transition from ductile to brittle failure in geometrically similar specimens. When failure is delayed after crack initiation, the size effect is mainly influenced by the energy released during macro-crack propagation. Conventional experimental studies on this phenomenon have typically utilized two-dimensional geometrically similar specimens, though they are often limited by laboratory constraints. While experimental studies on notched concrete beams under three-point bending (TPB) exist, their size is often restricted due to practical challenges in handling large specimens and also numerical modeling of large-scale fracture simulations remains limited due to high computational requirements. This research proposes an optimized finite element modeling approach to numerically examine the size effect on the fracture characteristics of notched concrete beams subjected to three-point bending (TPB). Beams with depths up to 1000 mm were analyzed using this approach. The numerical findings align well with experimental size-effect data from the literature, exhibiting the expected trends. Furthermore, fitting the results to Bažant’s size effect law demonstrated a strong correlation, validating the accuracy of the proposed numerical model

Phase-field modeling for investigating the effect of rebar positioning and uniform versus non-uniform corrosion on concrete fracture

Rebar corrosion significantly affects the overall performance and the service life of reinforced concrete (RC) structures due to the reduction in the bond strength between concrete and rebar, leading to the delamination of the concrete cover. Numerous studies have been conducted using experimental, analytical, and simulation methods to explore corrosion-induced damage. Regarding simulation methods, previous studies have focused on either uniform or non-uniform corrosion, without an overall comparison between these two scenarios in terms of crack development and displacement of rust expansion. Furthermore, in brittle materials such as concrete, the strain tensor is split into a tension part and a compression part, in which only the strain energy of the tension part controls the crack development. Therefore, this paper provides some novel aspects: (i) Two parts of the strain tensor are orthogonal in the context of the inner product with the elastic stiffness tensor behaving as a metric. This orthogonal condition combined with the phase-field modeling, helps to improve the mechanical behaviors of the materials; (ii) The numerical method (i) is used to simulate and compare the crack path and displacement due to rust expansion of RC structures under uniform and non-uniform corrosion conditions. Several RC cross-sections are conducted as follows: (a) Cross-sections containing one or multiple asymmetrically arranged rebars, with the constant rebar area fraction and the concrete cover thickness unchanged; (b) Cross-sections containing four symmetrically arranged rebars with the 10mm rebar diameter (D10) and the concrete cover thicknesses changed; (c) Cross-sections containing four symmetric D10 rebars and the pores. Through several aforementioned numerical simulation examples, this paper provides an overview of uniform versus non-uniform corrosion-induced fracture in the typical RC cross-sections. This can guide the selection of the appropriate rebar positioning for the realistic RC structures, helping to mitigate rapid deterioration due to the rebar corrosion

Modeling of the transition from transgranular to intergranular fracture at elevated temperatures in EI698 nickel alloy

In this study, an efficient computational method for modeling the transition from transgranular to intergranular fracture mechanisms based on phase field fracture theory is discussed. Structural heterogeneity of the material is modeled on the basis of Voroni diagrams. Parameters characterizing the mechanical properties of the material for the intergranular and transgranular space are the same for models of continuum mechanics. The location of crack initiation and the crack path in the proposed method controlled by the difference in the values of the critical energy release rate for the intergranular and transgranular spaces for the phase field model. The source code of the created and used finite element is an open source project and available to download from https://github.com/Andrey-Fog/ANSYS-USERELEMENT-PHFLD. The obtained results correlate well with previously conducted fractographic studies

Fatigue behaviour of high-strength low-alloy steel sheets: influence of loading direction and microstructure on microcrack initiation and growth

This work presents an in-depth study of the low-cycle fatigue behaviour of ferritic-pearlitic HSLA-420 high-strength steel sheets, with emphasis on the influence of loading direction on fatigue life and damage mechanisms. Plastic strain-controlled fatigue tests were conducted along the rolling (RD), transverse (TD), and diagonal (DD) directions. Despite the nearly isotropic tensile response associated with weak crystallographic texture and similar microstructural characteristics, fatigue life varied depending on the loading orientation. RD specimens showed the highest fatigue life, nearly doubling TD at low strain and remaining over 25% at high strain. DD behaved similarly to RD at low strain but approached TD at higher strain levels.  The Coffin–Manson relationship was linear in RD, while TD and DD showed bilinear trends with a slope change at Δεp/2 = 1 × 10⁻³. Transmission electron microscopy revealed that dislocation structure evolution during cycling was direction-dependent. In RD, intragranular slip bands within ferrite grains dominated and acted as primary crack initiation sites. In contrast, TD and DD exhibited subgrain structures near grain boundaries, promoting strain localization and intergranular crack nucleation. At higher strain amplitudes, compact subgrains reinforced by cementite particles favored intergranular crack propagation in TD and DD samples, contributing to reduced fatigue life

Damage mechanisms in hybrid composites: experimental characterisation and energy-based numerical analysis

This study analyses the failure mechanisms of bilayer hybrid composites, consisting of carbon and glass fibres embedded in an epoxy matrix, under bending loads. The objective is to evaluate how different hybrid configurations influence failure evolution and mechanical performance. To achieve this, specimens are submitted to 3-point bending tests, and 3D finite element models are developed to simulate the experimental setup. The numerical models incorporate a continuum damage mechanics model to capture intralaminar failure and a surface-based cohesive behaviour for interlaminar damage. The results show that hybrid laminates exhibit intermediate strength and displacement values compared to nonhybrid carbon and glass laminates, with the positioning of glass fibers significantly affecting bending force and displacement. Intralaminar damage is the primary failure mechanism in all configurations, followed by delamination. Additionally, placing glass fibers on the compression side reduces the overall damage, whereas placing them on the tensile side increases intralaminar failure before reaching the peak load. These findings contribute to optimizing the design of hybrid composites for bending applications by providing information about the relationship between material configuration and failure mechanisms, ultimately improving their structural efficiency and durability in engineering applications

Studying the strength and damageability of composite element in looped metal-composite joint under tensile loading

The article presents the results of computational and experimental studies of the strength and damageability of a connecting composite part in a metal-composite joint of isogrid and anisogrid structures made of polymer composite material under tension. The assessment of the minimal cross-sectional area of the connecting part was performed based on design calculations, taking into account strengthening during extrusion of the excess binder. The onset of failure in the contact zone with the steel element of the metal-composite joint was predicted based on experimental studies using model samples. A comparison was made between the calculation results for the tensile loading diagram, considering the physical nonlinear behavior of composite material in the joint zone, and the readings of strain gauges after testing the metal-composite joint. Damages and deformation of the connecting composite part under the tensile load was imaged using acoustic microscopy

Prediction of the tensile strength of FDM specimens based on Tsai Hill criteria

This study investigates the mechanical behavior of 3D-printed polyethylene terephthalate glycol (PETG) polymer specimens subjected to tensile and shear testing, with a particular focus on the influence of raster orientation and shell contour. Specimens were fabricated using Fused Deposition Modeling (FDM) at three raster angles (0°, 45°, and 90°) and tested using both a mechanical extensometer and a Digital Image Correlation (DIC) system. The results indicate a significant influence of raster orientation on tensile and shear properties. 0° specimens exhibited the highest tensile strength, as the filament alignment was parallel to the loading direction. In contrast, 45° specimens demonstrated more ductile behavior. While the shell contour had minimal effect on 0° and 45° specimens, it enhanced stiffness and ductility in 90° specimens. Furthermore, the Tsai-Hill criterion was applied to predict the tensile strength at a 45° orientation. These findings contribute to a deeper understanding of the anisotropic behavior of 3D-printed materials and highlight the importance of raster orientation in optimizing mechanical performance