Search Results (15)

This study investigates the structural performance of cellular cross-laminated timber (CCLT) through a nonlinear finite element model using Hill and Hashin damage criteria in Abaqus. This study evaluates these criteria in simulating CCLT’s mechanical behavior under bending and shear loading. Experimental validation included short-span and long-span bending tests, along with rolling shear tests. In bending simulations, the Hill criterion predicted maximum loads with a 7% error for long-span beams when modeling lumber as solid elements and the corrugated panel as shell elements. When the entire CCLT was modeled using shell elements, the error increased to 9%. For the short-span bending, the error remained at 8% regardless of element type. The Hashin model provided more accurate results, with deviations of 0.2% for long-span beams and 1% for short-span beams. Both models successfully predicted failure mechanisms, identifying tension failure in the lumber under long-span bending and shear failure in the corrugated core under short-span bending. In rolling shear tests, the Hill criterion underestimated the maximum shear load by 11%, while the Hashin criterion had a larger underestimation of 26%. Despite these discrepancies, both models effectively captured the nonlinear behavior of CCLT panels. These findings highlight the potential of Hill and Hashin criteria for modeling CCLT’s mechanical response, offering valuable insights into structural design applications. Full article

In Additive Manufacturing, wherein the construction of parts directly from 3D models is facilitated, a meticulous focus on enhancing the mechanical characteristics of these components becomes imperative. This study delves into the nuanced impact of the orientation of deposited layers on the mechanical properties of 3D printed Polylactic Acid (PLA) parts. Experimental testing, coupled with predictive modeling using Tsai–Hill and Tsai–Wu criteria, forms the crux of our investigation. The predicted ultimate strength from both criteria exhibits commendable agreement with the 3D printed specimens across a spectrum of orientation angles. Concurrently, Finite Element Simulations are meticulously executed to forecast mechanical behavior, taking into account the observed elasticity and plasticity in various orientations. Our observations reveal a significant augmentation in Young’s modulus and ductility/elongation—40% and 70%, respectively—when transitioning from θ = 0° to θ = 90°. Furthermore, the ultimate strength experiences a notable increase, leading to varied failure modes contingent upon θ. These findings underscore the pivotal role played by the orientation of printed layers in shaping the anisotropic behavior of 3D printed PLA parts, thereby integrating key process variables for optimization objectives. This study contributes valuable insights for professionals in the engineering, design, and manufacturing domains who seek to harness the advantages of 3D printing technology while ensuring that the mechanical integrity of 3D printed parts aligns with their functional requisites. It emphasizes the critical consideration of orientation as a design parameter in the pursuit of optimization objectives. Full article

The integration of mesoscale modeling and macroscale experimentation has emerged as a promising approach for understanding and predicting the mechanical behavior and fatigue performance of fiber-reinforced polymer composites. In this work, the mean field homogenization technique is implemented to predict the fatigue performance of the carbon-fiber-reinforced polymer composites under cyclic loading conditions. To predict the number of fatigue cycles, Modified Gerber criteria are used with the stress-based Tsai–Hill failure indicator. Fatigue strength factor (α) and creep rupture strength factor (β) are experimentally evaluated and further implemented in a computational approach to predict fatigue life cycles of the composite. The effect of composite constituents, stress ratio, and loading direction are investigated in detail against the fatigue performance of the composite. Fatigue cycles are predicted at individual matrix and fiber levels at various stress ratios of 0.2, 0.4, 0.6, and 0.8 at different loading inclinations. The experimental results are compared with the mesoscale S–N curves. Full article

In the last decade, fatigue damage models for fiber-reinforced polymer composites have been developed assuming the fracture energy equivalence hypothesis. These models are able to predict a fatigue life of composite laminates, but their identification requires a significant number of off-axial tests for various stress ratios. The present study proposes the stress ratio dependent model, which phenomenologically adopts a decrease in stiffness and residual strength of a unique ply according to experimental constant life diagrams. Hashin, Tsai–Hill, and the maximum stress failure criteria are utilized for damage initiation considering the residual strength of the ply. The obtained results indicate a sufficiency of using S-N curves for UD 0°, UD 45°, and UD 90° for identification of the model. The model was verified by S-N curves for UD 10°, UD 15°, and UD 30° and its applicability was demonstrated for prediction of a fatigue life of composite laminates with an arbitrary lay-up. The model is implemented into ABAQUS finite element software as a user subroutine. Full article

Most spoilers are made from a sandwich structure with a honeycomb component as its core. However, the honeycomb core is sensitive to water ingress, causing damage to the control surface due to its weak moisture-resistance behavior. This study aimed to conduct the design and analysis of an improved composite structure for a coreless spoiler. A spoiler design of an aircraft, the A320, was used for the case study. The weaknesses of a coreless spoiler were identified through finite element analysis via Abaqus software. Multi-spar and multi-rib designs were studied and compared for topological optimization. The variables used for evaluation were the Tsai–Hill failure index and the critical buckling load. The design with the most potential was considered for parametric optimization to obtain the most satisfactory configuration. The results showed that the upper skin of the spoiler without a honeycomb core failed the Tsai–Hill criteria. Furthermore, the results show that the multi-spar configuration outperformed the multi-rib configuration. The final multi-spar configuration achieved a mass reduction of 24% from the original spoiler and an additional 6% mass reduction by re-designing the internal structures without violating the design criteria. In conclusion, the weaknesses of the spoiler without a honeycomb core have been identified, and an improved design for a coreless spoiler has been proposed. Full article

Incorporating steel bars as reinforcement in glued laminated timber beams is a technique that aims at better structural performance, allowing the reduction of cross-sections. In the present research, based on experimental results from literature about the reinforcement of timbers beams, a parametric study was carried out with the aid of 164 numerical simulations performed within the scope of linear and nonlinear physical analysis via the finite element method to evaluate, with the aid of analysis of variance (ANOVA), the span, base, height, and the reinforcement ratio influence in the service force, ultimate force, and ultimate displacement. Multiple regression models evaluated by ANOVA were established to estimate the service and ultimate forces and ultimate and service displacements as a function of other variables. The results showed an average increase in the service load of 32% and 49%, and the ultimate load of 42.90% and 66.90%, for reinforcement rates of 2% and 4%, respectively. Regarding the multiple regression models, due to the good values obtained from the adjusted determination coefficients to estimate the values of the forces and the ultimate displacements, these can be used in the pre-design of glued laminated timber beams reinforced with steel bars. Full article

Governing void growth, stress triaxiality (η) is a crucial parameter in ductile damage prediction. η is defined as the ratio of mean stress to equivalent stress and represents loading conditions. Attempts at introducing material anisotropy in ductile damage models have started only recently, rendering necessary in-depth investigation into the role of η here. η is commonly derived via finite elemnt (FE) simulation. An alternative is presented here: based on analytical expressions, η is obtained directly from the strains in the critical zone. For anisotropic materials, η associated with a specimen varies with yield criterion and material (anisotropy). To investigate the meaning of triaxiality for anisotropic materials, metal sheets made of dual phase steel DP780, and zirconium alloy Zirlo are chosen. Analytical expressions for η are derived for three popular yield criteria: von Mises, Hill48 and Barlat89. Tensile tests are performed with uniaxial tension, notch, and shear specimens, and the local principal strains, measured via digital image correlation (DIC), are converted to h. The uniaxial tension case reveals that only the anisotropic yield criteria can predict the expected η = 1/3. The ramifications associated with anisotropy become apparent for notched specimens, where η differences are highest; for shear specimens, the yield criterion and material-dependence is relatively moderate. This necessitates η and, consequently, the triaxiality failure diagram (TFD) being accompanied by the underlying yield criterion and anisotropy parameters. As the TFD becomes difficult to interpret, it seems more advantageous to provide pairs of principal strain ratio β and failure strain. Suggestions for deriving representative β and η are made. Full article

Short-fiber reinforced composites are widely used for the mass production of high-resistance products with complex shapes. Efficient structural design requires consideration of plasticity and anisotropy. This paper presents a method for the calibration of a general material model for stress–strain curve prediction for short-fiber reinforced composites with different fiber mass fractions. A Mori–Tanaka homogenization scheme and the J2 plasticity model with layered defined fiber orientation were used. The hardening laws: power, exponential, and exponential and linear were compared. The models were calibrated using experimental results for melt front, orientation tensor analysis, fiber length, and diameter and tension according to ISO 527-2, for samples of PA6 which were either non-reinforced, or reinforced with 10%, 15%, 20%, and 30% carbon fiber mass fractions. The novelty of this study lies in the transition from the strain–stress space to the strain–stress–fiber fraction space in the approximation of the material model parameters. We found it necessary to significantly reduce the fiber aspect ratio for the correct prediction of the mechanical characteristics of a composite using the Mori–Tanaka scheme. This deviation was caused by the ideal solution of ellipsoidal inclusion in this homogenization scheme. The calculated strength limits using Tsai–Hill failure criteria, based on strain, could be used as a first approximation for failure prediction. Full article

In composite materials, the use of failure criteria is necessary to determine the failure forces. Various failure criteria are known, from the simplest ones that compare individual stresses with the corresponding strength, to more complex ones that take into account the sign and direction of the stress, as well as mutual interactions of the acting stresses. This study investigates the application of the maximum stress, Tsai-Hill, Tsai-Wu, Puck, Hoffman and Hashin criteria to beech plywood made from a series of plies of differently oriented beech veneers. Specimens were cut from the manufactured boards at various angles and loaded by bending to failure. The mechanical properties of the beech veneer were also determined. The specimens were modelled using the finite element method with a composite modulus and considering the different failure criteria where the failure forces were calculated and compared with the measured values. It was found that the calculated forces based on all failure criteria were lower than those measured experimentally. The forces determined using the maximum stress criterion showed the best agreement between the calculated and measured forces. Full article

Determining the appropriate boundary conditions of a structure is a very important aspect in the failure analysis. In experimental tests, the method of compressing composite samples significantly influences the obtained results. In numerical studies, there is a problem of correctly defining the boundary conditions applied in real object. Therefore, many numerical tests on samples should be undertaken to observe their behavior and to determine ultimate load. The present work includes study to determine the impact of boundary conditions on the thin-walled laminated angle column under compression. The phenomenon of buckling and the post-buckling bahavior of columns were investigated experimentally and numerically. First, the real simply supported angle columns subjected to uniform shortening are tested. Due to the stress concentration between the real sample and the grips, a flexible pads were used. Experimental tests are carried out on the universal testing machine. The deformations of columns were measured using the non-contact Aramis System. The composite material condition was monitored by acoustic emission using the Vallen Systeme with piezoelectric sensors. Next, the numerical calculations in Abaqus software based on the finite element method are performed to validate the empirical results. To determine the influence of the boundary conditions, two numerical models of the system with and without flexible pads are developed. To estimate damage initiation load in numerical models a different damage criteria ( Tsai-Hill, Tsai-Wu, Azzi-Tsai-Hill, Hashin) are used. Based on the results specified that the model with elastic pads more accurately reflects the actual behavior of the L-profile element under compression. It was supported, i.e., by good agreement of flanges deflection (the equilibrium paths) with experimental results. Furthermore, a qualitative and quantitative agreement of damage initiation load were obtained using Hashin criteria (error 4.61%). Full article

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is still an ongoing global health crisis. Immediately after the inhalation of SARS-CoV-2 viral particles, alveolar type II epithelial cells harbor and initiate local innate immunity. These particles can infect circulating macrophages, which then present the coronavirus antigens to T cells. Subsequently, the activation and differentiation of various types of T cells, as well as uncontrollable cytokine release (also known as cytokine storms), result in tissue destruction and amplification of the immune response. Vitamin D enhances the innate immunity required for combating COVID-19 by activating toll-like receptor 2. It also enhances antimicrobial peptide synthesis, such as through the promotion of the expression and secretion of cathelicidin and β-defensin; promotes autophagy through autophagosome formation; and increases the synthesis of lysosomal degradation enzymes within macrophages. Regarding adaptive immunity, vitamin D enhances CD4⁺ T cells, suppresses T helper 17 cells, and promotes the production of virus-specific antibodies by activating T cell-dependent B cells. Moreover, vitamin D attenuates the release of pro-inflammatory cytokines by CD4⁺ T cells through nuclear factor κB signaling, thereby inhibiting the development of a cytokine storm. SARS-CoV-2 enters cells after its spike proteins are bound to angiotensin-converting enzyme 2 (ACE2) receptors. Vitamin D increases the bioavailability and expression of ACE2, which may be responsible for trapping and inactivating the virus. Activation of the renin–angiotensin–aldosterone system (RAS) is responsible for tissue destruction, inflammation, and organ failure related to SARS-CoV-2. Vitamin D inhibits renin expression and serves as a negative RAS regulator. In conclusion, vitamin D defends the body against SARS-CoV-2 through a novel complex mechanism that operates through interactions between the activation of both innate and adaptive immunity, ACE2 expression, and inhibition of the RAS system. Multiple observation studies have shown that serum concentrations of 25 hydroxyvitamin D are inversely correlated with the incidence or severity of COVID-19. The evidence gathered thus far, generally meets Hill’s causality criteria in a biological system, although experimental verification is not sufficient. We speculated that adequate vitamin D supplementation may be essential for mitigating the progression and severity of COVID-19. Future studies are warranted to determine the dosage and effectiveness of vitamin D supplementation among different populations of individuals with COVID-19. Full article

Steel reinforcements in concrete tend to corrode and this process can lead to structural damage. Fiber-reinforced polymer (FRP) reinforcements represent a viable alternative for structures exposed to aggressive environments and have many possible applications where superior corrosion resistance properties are required. The use of FRP rebars as internal reinforcements for concrete, however, is limited to specific structural elements and does not yet extend to the whole structure. The reason for this relates to the limited availability of curved or shaped reinforcing FRP elements on the market, as well as their reduced structural performance. This article presents a state-of-the art review on the strength degradation of curved FRP composites, and also assesses the performance of existing predictive models for the bend capacity of FRP reinforcements. Previous research has shown that the mechanical performance of bent portions of FRP bars significantly reduces under a multiaxial combination of stresses. Indeed, the tensile strength of bent FRP bars can be as low as 25% of the maximum tensile strength developed in a straight counterpart. In a significant number of cases, the current design recommendations for concrete structures reinforced with FRP were found to overestimate the bend capacity of FRP bars. A more accurate and practical predictive model based on the Tsai–Hill failure criteria is also discussed. This review article also identifies potential challenges and future directions of research for exploring the use of curved/shaped FRP composites in civil engineering applications. Full article

This paper describes an optimization study of a spherical composite submersible pressure hull employing a genetic algorithm (GA) in ANSYS. A total of five lay-up arrangements were optimized for three unidirectional composites carbon/epoxy, glass/epoxy, and boron/epoxy. The minimization of the buoyancy factor $\left(B.F\right)$ was selected as the design optimization objective. The Tsai-Wu and Tsai-Hill failure criteria and buckling strength factor $\left(\lambda \right)$ were used as the material failure and instability constraints. To determine the effect of geometric non-linearity and imperfections on the optimized design, a non-linear buckling analysis was also carried out for one selected optimized design in ABAQUS. The non-linear buckling analysis was carried out using the modified RIKS procedure, in which the imperfection size changed from 1 to 10 mm. A maximum decrease of 65.937% in buoyancy factor $\left(B.F\right)$ over an equivalent spherical steel pressure hull was computed for carbon/epoxy. Moreover, carbon/epoxy displayed larger decreases in buoyancy factor $\left(B.F\right)$ in the case of 4 out of a total of 5 lay-up arrangements. The collapse depth decreased from 517.95 m to 412.596 m for a 5 mm lowest mode imperfection. Similarly, the collapse depth decreased from 522.39 m to 315.6018 for a 5 mm worst mode imperfection. Full article

A precise characterization of material behavior is necessary to identify yield criteria or hardening laws for an accurate numerical design of sheet metal forming processes. Current models like Yld2000-2d or Hill’48 do not consider the plane strain state, though this condition is primary cause of failure in deep drawing. It is anticipated that an improved yield locus contour which considers the stress under plane strain conditions leads to better results in numerical simulations of a deep drawing process. Within this contribution, a new experimental setup to characterize both principal stress components under plane strain as additional input data for material modelling is presented. Therefore, hydraulic bulge tests are carried out with a novel elliptical die, which implements a plane strain condition. Moreover, the improvement of the material model is investigated exemplarily for the three sheet metal alloys DC06, DP600 and AA5182. The resulting material parameters are used to identify the yield locus for plane strain by varying the yield locus exponent of Yld2000-2d. The results prove that considering plane strain yield locus results in a better sheet thickness distribution in comparison to conventional modelling of the deep drawing process. Full article

The maximum force criteria and their derivatives, the Swift and Hill criteria, have been extensively used in the past to study sheet formability. Many extensions or modifications of these criteria have been proposed to improve necking predictions under only stretching conditions. This work analyses the maximum force principle under stretch-bending conditions and develops two different approaches to predict necking. The first is a generalisation of classical maximum force criteria to stretch-bending processes. The second approach is an extension of a previous work of the authors based on critical distance concepts, suggesting that necking of the sheet is controlled by the damage of a critical material volume located at the inner side of the sheet. An analytical deformation model is proposed to characterise the stretch-bending process under plane-strain conditions. Different parameters are considered, such as the thickness reduction, the gradient of variables through the sheet thickness, the thickness stress and the anisotropy of the material. The proposed necking models have been successfully applied to predict the failure in different materials, such as steel, brass and aluminium. Full article