arXiv subjects

Marco Salviato

Publications and source records attributed to Marco Salviato.

At least 19 recordsLinked to original sources

arXiv2026

Experimental characterization of cohesive laws for mode-II interlaminar fracture in geometrically scaled composites using through-thickness deformation analysis

This work proposes an experimental framework to characterize a cohesive law for mode-II interlaminar fracture and demonstrates its implementation. For a size effect study, geometrically scaled end-notched flexure specimens were tested using microscopic and macroscopic digital image correlation (DIC) systems. The fracture energy was characterized using a compliance calibration method and Bažant's type-II size effect law for comparison. In the proposed experimental framework, the DIC data were post-processed using three steps: coordinate transformation, curve fitting, and through-thickness deformation analysis. Different magnitudes of separation values were measured from different sizes at fracture loads, implying size effect and partial development of cohesive laws. Modeling and simulations were intended to validate the proposed method and demonstrate the utilization of the experimental data. Additionally, challenges related to finding a single cohesive law for geometrically scaled specimens of a single material were exposed. A single cohesive law for the scaled specimens was developed and proposed as a material property of the specimen material. The fracture energy of the single law was smaller than the energy obtained from the size effect analysis, while the sizes of fracture process zones at fracture loads were smaller than the experimental measurements. However, the global fracture behaviors of the models showed good agreement with the experimental data of the mid-size specimen while showing reasonable agreement with the other sizes. Furthermore, the single law successfully captured local fracture behaviors by showing partial cohesive zone development at the fracture loads and matching the microscopic measurement of the separation values.

physics.app-ph↗

arXiv2023

Rethinking Ductility -- A Study Into the Size-Affected Fracture of Polymers

Ductility quantifies a material's capacity for plastic deformation, and it is a key property for preventing fracture driven failure in engineering parts. While some brittle materials exhibit improved ductility at small scales, the processes underlying this phenomenon are not well understood. This work establishes a mechanism for the origin of ductility via an investigation of size-affected fracture processes and polymer degree of conversion (DC) in two-photon lithography (TPL) fabricated materials. Microscale single edge notch bend ($μ$SENB) specimens were written with widths from 8 to 26 $μ$m and with different laser powers and post-write thermal annealing to control the DC between 17\% and 80\%. We find that shifting from low to high DC predictably causes a $\sim$3x and $\sim$4x increase in strength and bending stiffness, respectively, but that there is a corresponding $\sim$6x decrease in fracture energy from 180 $J/m^2$ to 30 $J/m^2$. Notably, this reduced fracture energy is accompanied by a ductile-to-brittle transition (DBT) in the failure behavior. Using finite element analysis, we demonstrate that the DBT occurs when the fracture yielding zone size ($r_p$) approaches the sample width, corresponding with a known fracture size-affected transition from flaw-based to strength-based failure. This finding provides a crucial insight that ductility is a size-induced property that occurs when features are reduced below a characteristic fracture length scale and that strength, stiffness, and toughness alone are insufficient predictors of ductility.

cond-mat.soft↗

arXiv2023

Effects of Thermal Modification on the Flexure Properties, Fracture Energy, and Hardness of Western Hemlock

This study investigates the effect of thermal modification on the flexural properties, transverse fracture energy, and hardness of western hemlock, a material which is finding increasing applications in construction. Flexure tests on specimens featuring longitudinal and transverse grains showed that thermal modification at 167C slightly improves the flexural modulus and strength and leads to less statistical variability compared to unmodified samples. On the other hand, the fracture and Janka hardness tests revealed a more pronounced brittleness of the thermally modified samples. In fact, the total mode I fracture energy of modified Single Edge Notch Bending (SENB) samples was about 47% lower for radial-longitudinal systems and 60% lower for tangential-longitudinal systems. Similarly, the average Janka hardness in the tangential, radial, and transverse planes was 8.5%, 3.9%, and 9.4% lower in the modified specimens, respectively. The results presented in this work show that thermal modification can have a significant effect on the fracturing behavior of western hemlock and its energy dissipation capabilities. For design, this must be taken into serious consideration as these properties significantly influence the damage tolerance of this wood in the presence of stress concentrations such as e.g., those induced in bolted joints and cut outs. Fracture energy and hardness are also strongly correlated to ballistic performance.

cond-mat.soft↗

arXiv2023

Size Effect and Scaling in Quasi-static and Fatigue Fracture of Graphene Polymer Nanocomposites

This work investigated how the structure size affects the quasi-static and fatigue behaviors of graphene polymer nanocomposites, a topic that has been often overlooked. The results showed that both quasi-static and fatigue failure of these materials scale nonlinearly with the structure size due to the presence of a significant Fracture Process Zone (FPZ) ahead of the crack tip induced by graphene nanomodification. Such a complicated size effect and scaling in either quasi-static or fatigue scenario cannot be described by the Linear Elastic Fracture Mechanics (LEFM), but can be well captured by the Size Effect Law (SEL) which considers the FPZ. Thanks to the SEL, the enhanced quasi-static and fatigue fracture properties were properly characterized and shown to be independent of the structure size. In addition, the differences on the morphological and mechanical behaviors between quasi-static fracture and fatigue fracture were also identified and clarified in this work. The experimental data and analytical analyses reported in this paper are important to deeply understand the mechanics of polymer-based nanocomposite materials and even other quasi-brittle materials (e.g., fiber-reinforced polymers or its hybrid with nanoparticles, etc.), and further advance the development of computational models capable of capturing size-dependent fracture of materials in various loading conditions.

physics.app-ph↗

arXiv2023

Effects of Average Number of Platelets Through the Thickness and Platelet Width on the Mechanical Properties of Discontinuous Fiber Composites

In this study, we experimentally and numerically investigate the evolution of the tensile material properties of Discontinuous Fiber Composites (DFCs) with an increasing average number of platelets through the thickness for two different platelet widths. The results show that both the number of platelets and the platelet width have significant effects on the tensile modulus and strength. We find that not only the average mechanical properties but also their coefficients of variation change according to the different DFC mesostructures. To understand the relationship between material morphology at the mesoscale and corresponding material properties, we developed a random platelet mesostructure generation algorithm combined with explicit finite element models. Leveraging the computational tools, we find that moduli and strength increase with increasing average number of platelets through the thickness. The increasing trend continues until reaching an asymptotic limit at about 45 layers through the thickness for the narrow platelets and 27 layers for the square platelets. In the study, we address the importance of having accurate simulations of the mesostructure to match not only the average modulus and strength but also their associated coefficients of variation. We show that it is possible to accurately predict the tensile material properties of DFCs, including their B-basis design values. This is a quintessential condition for the adoption of DFCs in structural applications.

cond-mat.soft↗

arXiv2022

The Gap Test: Effects of Crack Parallel Compression on Fracture in Carbon Fiber Composites

This paper explores the global Mode I fracture energy of a carbon fiber composite subject to a biaxial stress state at a crack tip, specifically in which one stress component is compressive and parallel to the crack. Based on an experimental technique previously coined as The Gap Test and Bazant's Type II Size Effect Law, it is found that there is a monotonic decrease in the Mode I fracture energy as the crack parallel compressive stress increases. Compared to the nominal value of fracture energy, where no crack parallel compression is applied, the fracture energy is observed to decrease by up to 37% for a compressive stress equal to 44% of the compressive failure limit of the composite. This weakening effect is attributed to splitting cracks that are induced at the crack tip due to the crack parallel compression, which are identified via crack tip photomicroscopy. This is a novel result that challenges the century old hypothesis of fracture energy being a constant material property and further, shows for the first time that crack parallel compression leads to a composite structure being dangerously weaker than expected. The experimental campaign is also buttressed with a computational campaign that provides a framework capable of capturing the effects of crack parallel compression. Through the use of the crack band model, which correctly characterizes the fracture process zone tensorially, coupled with a fully tensorial damage law, the simulated results provide satisfactory agreement with the experimental data. Conversely, when a reduced tensorial damage law defines the crack band it is shown that the structural strength and fracture energy are dangerously overpredicted. This emphasizes the importance of using a crack band model coupled with a fully tensorial damage law to accurately predict fracture in composites.

cond-mat.mtrl-sci↗

arXiv2021

Stress Distributions and Notch Stress Intensity Factors in Multimaterial V-notches Under Antiplane Shear and Torsion

This study investigates how the insertion of multimaterial circular regions embracing the tip of a finite V-notch can be used to reduce the Notch Stress Intensity Factors (NSIFs) in structures subjected to antiplane shear or torsion. Towards this goal, this work presents a novel theoretical framework to calculate stress distributions and NSIFs in closed-form. Thanks to the new solution, it is shown that by tuning multimaterial region radii and elastic properties it is possible to significantly reduce the NSIFs and stress concentrations at the material interfaces. To investigate whether the proposed multimaterial system translates into increased structural capacity even in the presence of significant nonlinear deformations, computational simulations were conducted using nonlinear hyperelastic-damage and elasto-plastic-damage models. The preliminary results show increases of structural capacity up to 46% and of nominal strain at failure of up to 86% at the expenses of only a 8% reduction in structural stiffness. It is expected that a similar approach can be extended to other loading conditions (e.g. mode I and mode II, and fatigue) and that even larger gains can be obtained by performing thorough optimization studies.

cond-mat.mtrl-sci↗

arXiv2021

Effects of Out Time on the Mechanical and Fracture Properties of Chopped Fiber Composites Made From Repurposed Aerospace Prepreg Scrap and Waste

In this study, the effects of prepreg out time on the mechanical and fracture properties of Discontinuous Fiber Composites (DFCs) are investigated. Carbon fiber prepregs are aged at 0x, 1x, 2x, and 3x the out life in an environmental chamber at constant temperature and humidity. Degree of cure is measured via Differential Scanning Calorimetry (DSC) while tension, compression, and shear tests are performed to investigate the effects that aging has on these mechanical properties. For the first time, Mode I intra-laminar fracture and its size effect are also investigated by means of fracture tests on geometrically-scaled Single Edge Notch Tension (SENT) specimens. From the tension, compression, and shear experiments it is seen that the out time has no effect on the elastic moduli. However, the strength increases with increasing age of the specimens for all the loading conditions. The percent increase compared to the non-aged material ranges from 15% to 33%. This is likely caused by plasticization of the matrix with age, allowing for higher energy absorption. More complex trends are reported for the SENT specimens for all the sizes. It is found that the fracture energy and characteristic length initially decrease with age, and then finally increase for the longest out time. This trend is owed to two factors with countering effects on the fracture behavior: 1) the increase of the average number of platelets with increasing aging due to increase in resin viscosity, and 2) the plasticization of the matrix with aging. The results from this study suggest that Discontinuous Fiber Composites (DFCs) made from reused materials can have equal, if not better, performance than non-aged DFCs. The experimental data presented in this work can be used as a baseline to design DFC composite components made from repurposed prepreg scrap and waste.

cond-mat.mtrl-sci↗

arXiv2021

Effect of Temperature History During Additive Manufacturing on Crystalline Morphology of Polyether Ether Ketone

Additive manufacturing parameters of high-performance polymers greatly affect the thermal history and consequently quality of the end-part. For fused deposition modeling (FDM), this may include printing speed, filament size, nozzle, and chamber temperatures, as well as build plate temperature. In this study, the effect of thermal convection inside a commercial 3D printer on thermal history and crystalline morphology of polyetheretherketone (PEEK) was investigated using a combined experimental and numerical approach. Using digital scanning calorimetry (DSC) and polarized optical microscopy (POM), crystallinity of PEEK samples was studied as a function of thermal history. In addition, using finite element (FE) simulations of heat transfer, which were calibrated using thermocouple measurements, thermal history of parts during virtual 3D printing was evaluated. By correlating the experimental and numerical results, the effect of printing parameters and convection on thermal history and PEEK crystalline morphology was established. It was found that the high melting temperature of PEEK, results in fast melt cooling rates followed by short annealing times during printing, leading to relatively low degree of crystallinity (DOC) and small crystalline morphology.

physics.app-ph↗

arXiv2020

Elastic and Fracture Behavior of Three-Dimensional Ply-to-Ply Angle Interlock Woven Composites: Through-Thickness, Size Effect, and Multiaxial Tests

This work presents a comprehensive investigation of the elastic and fracture behavior of ply-to-ply angle interlock three-dimensional woven composites. The research investigated novel splitting and wedge-driven out-of-plane fracture tests to shed light on the tensile fracture behavior in the thickness direction and to provide estimates of the out-of-plane tensile strength and fracture energy. In addition, size effect tests on geometrically-scaled Single Edge Notch Tension (SENT) specimens were performed to fully characterize the intra-laminar fracture energy of the material and to study the scaling of structural strength in this type of three-dimensional composites. The results confirmed that size effect in the structural strength of these materials is significant. In fact, even if the range of sizes investigated was broader than in any previous size effect study on traditional laminated composites and two-dimensional textile composites, all the experimental data fell in the transition zone between quasi-ductile and brittle behavior. This implies strong damage tolerance of the investigated three-dimensional composites. The analysis of the data via Bazant's Type II Size Effect Law (SEL) enabled the objective characterization of the intra-laminar fracture energy of three-dimensional composites for the first time. Finally, Arcan rig tests combined with X-ray micro-computed tomography allowed unprecedented insights on the different damage mechanisms under multi-axial nominal loading conditions, particularly tension-dominated and shear-dominated conditions.

cond-mat.mtrl-sci↗

arXiv2020

REPORT: Investigation on Curvilinear Anisotropy via Isogeometric Analysis (IGA)

The advent of multi-material additive manufacturing and automated composite manufacturing has enabled the design of structures featuring complex curvilinear anisotropy. To take advantage of the new design space, efficient computational approaches are quintessential. In this study, we explored a new NURBS-based Isogeometric Analysis (IGA) framework for the simulation of curvilinear fiber composites and we compared it to standard Finite Element Analysis (FEA). A plate featuring a semi-circular notch under tensile loading with different fiber configurations served as a case study. We showed that, thanks to the exact geometric representation and the enriched continuity between elements, NURBS-based IGA outperforms classical FEA in terms of computational efficiency, time-consumption, and estimation quality of field variables for same number of degrees-of-freedom. To further demonstrate the use of the IGA framework, we performed optimization studies aimed at identifying the fiber paths minimizing stress concentration and Tsai-Wu failure index. The model showed that curvilinear anisotropy can be effectively harnessed to reduce the stress concentration of up to 82 % compared to unidirectional composites without affecting the overall plate stiffness significantly.

physics.app-ph↗

arXiv2020

Ply-drop design of non-conventional composites using Bayesian optimization

Automated Fiber Placement (AFP) technology provides a great ability to efficiently produce large carbon fiber reinforced composite structures with complex surfaces. AFP has a wide range of tow placement angles, and the users can design layup angles so that they can tailor the performance of the structure. However, despite the design freedom, the industry generally adopts a layering of 0 deg, 90 deg, and plus-minus 45 deg ply-drop angles. Here, we demonstrate the optimization of ply-drop angles of non-conventional composites. Specifically, we use classical laminate theory and Bayesian optimization to achieve better layup angles in terms of stiffness, Tsai-Wu failure criteria, and manufacturing time. Our approach shows its effectiveness in designing carbon fiber composite structures using unconventional angles in terms of both mechanical properties and production efficiency. Our method has the potential to be used for more complex scenarios, such as the production of curved surfaces and the utilization of finite element analysis.

physics.app-ph↗

arXiv2020

Molecular dynamics simulation for cross-linking processes and material properties of epoxy resins with the first principle calculation combined with global reaction route mapping algorithms

Herein, epoxy resin is cured by coupling quantum chemical (QC) calculations with molecular dynamics (MD) simulations that enable parameter-free prediction of material characteristics. A polymer network is formed by the reaction between base resin and curing agent. The reaction uses activation energy and heat of formation data obtained by first-principle calculations coupled with global reaction route mapping (GRRM) algorithms. Density, glass transition temperature, Young's modulus, and curing conversion is used to validate the procedure. Experimental and simulation results indicate that base resin with multi-functional reaction groups increases glass-transition temperature and Young's modulus because of cross-linked formations at the molecular scale.

cond-mat.soft↗

arXiv2019

Aerogami: Composite Origami Structures as Active Aerodynamic Control

This study explores the use of origami composite structures as active aerodynamic control surfaces. Towards this goal, two origami concepts were designed leveraging a combination of analytical and finite element modeling, and computational fluid dynamics simulations. Wind tunnel tests were performed at different dynamic pressures in conjunction with two different active control laws to test the capability of obtaining desired drag values. The experiments revealed excellent structural rigidity and folding characteristics under aerodynamic loading. Future work will focus on developing advanced origami designs that allow for more deterministic folding as well as improved weight, stiffness, and fatigue characteristics in the use of materials. Upon completion of these improvements, it is anticipated that full-scale testing on a vehicle could be meaningfully conducted.

physics.app-ph↗

arXiv2019

Micro-Computed Tomography Analysis of Damage in Notched Composite Laminates Under Multi-Axial Fatigue

The broad application of polymer composites in engineering demands the deep understanding of the main damage mechanisms under realistic loading conditions and the development of proper physics-based models. Towards this goal, this study presents a comprehensive characterization of the main damage mechanisms in a selection of notched composite structures under multiaxial fatigue loading. Thanks to a synergistic combination of X-ray micro-computed tomography ($μ$-CT) and Digital Image Correlation (DIC), the main failure modes are identified while the crack volume associated to each mechanism is characterized. This study provides unprecedented quantitative data for the development and validation of computational models to capture the fatigue behavior of polymer composite structures.

physics.app-ph↗

arXiv2019

A Study on the Multi-axial Fatigue Failure Behavior of Notched Composite Laminates

Composite structures must endure a great variety of multi-axial stress states during their lifespan while guaranteeing their structural integrity and functional performance. Understanding the fatigue behavior of these materials, especially in the presence of notches that are ubiquitous in structural design, lies at the hearth of this study which presents a comprehensive investigation of the fracturing behavior of notched quasi-isotropic [+45/90/$-$45/0]$_{s}$ and cross-ply [0/90]$_{2s}$ laminates under multi-axial quasi-static and fatigue loading. The investigation of the S-N curves and stiffness degradation, and the analysis of the damage mechanisms via micro-computed tomography clarified the effects of the multi-axiality ratio and the notch configuration. Furthermore, it allowed to conclude that damage progression under fatigue loading can be substantially different compared to the quasi-static case. Future efforts in the formulation of efficient fatigue models will need to account for the transition in damaging behavior in the context of the type of applied load, the evolution of the local multi-axiality ratio, the structure size and geometry, and stacking sequence. By providing important data for model calibration and validation, this study represents a first step towards this important goal.

physics.app-ph↗

arXiv2019

Mode I and II Interlaminar Fracture in Laminated Composites: A Size Effect Study

This work investigates the mode I and II interlaminar fracturing behavior of laminated composites and the related size effects. Fracture tests on geometrically scaled Double Cantilever Beam (DCB) and End Notch Flexure (ENF) specimens were conducted to understand the nonlinear effects of the cohesive stresses in the Fracture Process Zone (FPZ). The results show a significant difference between the mode I and mode II fracturing behaviors. It is shown that, while the strength of the DCB specimens scales according to the Linear Elastic Fracture Mechanics (LEFM), this is not the case for the ENF specimens. Small specimens exhibit a pronounced pseudo-ductility with limited size effect and a significant deviation from LEFM, whereas larger specimens behave in a more brittle way, with the size effect on nominal strength closer to that predicted by LEFM. This behavior, due to the significant size of the Fracture Process Zone (FPZ) compared to the specimen size, needs to be taken into serious consideration. It is shown that, for the specimen sizes investigated in this work, neglecting the non-linear effects of the FPZ can lead to an underestimation of the fracture energy by as much as 55%, with an error decreasing for increasing specimen sizes. Both the mode I and II test data can be captured very accurately by Bažant's type II Size Effect Law (SEL).

cond-mat.mtrl-sci↗

arXiv2019

Effect of the Thickness on the Fracturing Behavior of Discontinuous Fiber Composite Structures

In this study, we investigate experimentally and numerically the mode I intra-laminar fracture and size effect of Discontinuous Fiber Composites (DFCs) as a function of the structure thicknesses. By testing geometrically-scaled Single Edge Notch Tension (SENT) specimens a notable structure size effect on the nominal strength of DFCs is identified. As the specimen size increases, the nominal strength decreases. For small specimens, we find a limited size effect with enhanced pseudo-ductility and a strong divergence from Linear Elastic Fracture Mechanics (LEFM). For sufficiently large specimen sizes, the scaling of the nominal strength follows closely LEFM with a strong brittle failure. As the thickness increases, the size effect decreases. We identify the fracture energy and the effective size of the fracture process zone as a function of the thickness of the structure. To do so, we integrate equivalent fracture mechanics and stochastic finite element modeling. Experimentally, we collect the nominal strength of geometrically-scaled Single Edge Notch Tension (SENT) specimens. The numerical stochastic model captures the complex, inhomogeneous mesostructure of DFCs by explicitly generating the platelets. From the integrated analysis, it is found that the fracture energy depends significantly on the structure thickness. It is shown to increase gradually up to 2 mm and saturates after 3 mm to a value of 57.77 N/mm, which is 4.81 times larger than a typical aluminum alloy.

physics.app-ph↗