Pedro P. Camanho

Pedro P. Camanho
University of Porto | UP · Departamento de Engenharia Mecânica

PhD

About

270
Publications
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17,467
Citations

Publications

Publications (270)
Article
A new 3D elastoplastic damage model is proposed to predict the plastic deformation and the progressive failure of unidirectional laminated composite materials at the meso-scale level. A non-associated flow rule is employed to properly define the volumetric plastic strains. The damage evolution laws are defined to account for the failure mechanisms...
Article
Full-text available
We performed in-situ tensile tests on two carbon fibre/epoxy composites with continuous scanning using synchrotron computed tomography (CT). Both composites were cross-ply laminates, and two specimens were tested for each composite. The voxel size was sufficiently small to recognize individual fibres and fibre breaks. For each test, 16-19 volumes w...
Article
Longitudinal tensile failure of unidirectional fibre-reinforced composites remains difficult to predict accurately. The key underlying mechanism is the tensile failure of individual fibres. This paper objectively measured the relevant input data and performed a detailed experimental validation of blind predictions of six state-of-the-art models usi...
Article
This work presents the results of an experimental study performed in carbon/epoxy composite materials manufactured using a ply-level hybridization technique. The aim of the study is to investigate the potential of such hybridization technique to promote pseudo-ductile failure, and to enhance fracture toughness. Two thin-ply carbon-epoxy systems and...
Article
This work represents the first step towards the application of machine learning techniques in the prediction of statistical design allowables of composite laminates. Building on data generated analytically, four machine algorithms (XGBoost, Random Forests, Gaussian Processes and Artificial Neural Networks) are used to predict the notched strength o...
Conference Paper
Full-text available
Industry statistics show that lightning strikes account for approximately 34% of all in-service damage caused to aeroplanes. Because low-conductive CFRPs are more vulnerable to lightning-induced damage than metals, their extensive use in airframes, which in new generation wide-body aeroplanes ascends to over 50% in structural weight and 90% in surf...
Article
Many models for prediction of longitudinal tensile failure of unidirectional (UD) composites have been developed in the last decades. These models require significant assumptions and simplifications, but their consequences for the predictions are often not clearly understood. This paper therefore presents a blind benchmark of seven different models...
Article
Full-text available
Four different methods to experimentally determine the J-curve of quasi-brittle materials are analysed and discussed in this work. The first two methods measure the integral of the cohesive law, J (ω), from an initial notch. However, the correct definition of the notch geometry is of critical importance for an accurate identification of the cohesiv...
Article
For the past six years, we have been benefiting from the discovery by [1] that the trace of the plane stress stiffness matrix (tr(Q)) of an orthotropic composite is a fundamental and powerful scaling property of laminated composite materials. Algebraically, tr(Q) turns out to be a measure of the summation of the moduli of the material. It is, there...
Article
The apparent crack resistance curves associated with longitudinal tensile failure of carbon fibre reinforced epoxy composite systems with ply thicknesses of 0.075 mm, 0.134 mm and 0.268 mm are determined experimentally from the size effect law of geometrically similar double edge notch tension cross-ply specimens. An increase in notched strength as...
Article
The introduction of the spread-tow thin-ply technology enabled the development of composite plies as thin as 0.020 mm. The availability of composite plies with a broader thickness range makes the understanding of the effects of ply thickness more pertinent than ever, therefore, a comprehensive literature review is presented in this paper. The micro...
Article
Aerospace-grade unidirectional carbon microfiber reinforced epoxy prepreg composite laminates were reinforced in the relatively weak interlaminar regions with high densities (>10 billion nanofibers per cm²) of uniformly-distributed vertically aligned carbon nanotubes (A-CNTs), creating a hierarchical architecture termed “nanostitch”. Such nanostitc...
Article
X-ray micro-computed tomography (μCT) is used to quantify morphology in AS4/8552 (autoclave) and IM7/M56 (Out-of-Autoclave, OoA) aerospace-grade advanced unidirectional-ply carbon fiber prepreg composites, revealing several previously unreported features. The micron-scale (1 μm voxel size) three-dimensional datasets combined with automated, objecti...
Article
Typical composite structures are characterized by having brittle failure and thus higher safety factors. Alternatively, hybrid composites with pseudo-ductile behaviour can contribute to safer and more efficient designs. The objective of this work is to achieve a “pseudo-ductile” behaviour in the response of unidirectional hybrid composites when sub...
Article
This paper presents the application of a composite damage model to predict the edge impact and compression after edge impact (CAEI) response of CFRP laminates. First, a mesh sensitivity analysis is performed showing that the mesh needs to be sufficiently fine to accurately capture the permanent out-of-plane deformation at the impact location, which...
Article
Fibres Reinforced Polymers (FRPs) are found in several applications in aeronautics, space and in the automotive industry. These applications are exposed to loading conditions, including impact, which results in a complex mechanical response that is vital to accurately predict. This is particularly important for a new generation of thermoplastic-bas...
Article
This paper presents the development and validation of a mesoscale numerical model for predicting damage and failure of bolted joints in laminated composites with different configurations and geometries. Double-shear and single-shear composite bolted joints with different widths and end distances were analyzed. The composite material model combined...
Article
The development of numerical tools to complement the experimental determination of structural design parameters is of key importance to hasten the certification process of new materials and structures. In this work, a methodology to simulate elastic and inelastic deformation of composite laminates at the subcomponent level based on finite element a...
Article
This paper presents the development and validation of a mesoscale numerical model for predicting the bearing damage and failure of composite laminates reinforced by unidirectional fibers. Firstly, half-hole pin bearing tests were carried out on composite laminates with both quasi-isotropic and soft lay-ups, as well as in specimens with variations i...
Article
A spring element model that takes into account the dynamic effects associated with fibre failure in composite materials is presented. The model is implemented in a parallel environment to allow a better performance in the prediction of the complex mechanisms associated with longitudinal tensile failure. The model is used to identify the changes in...
Article
To simplify the analysis and characterisation of composite laminates, an invariant-based approach to stiffness that takes the trace of the plane stress stiffness matrix as a material property was recently proposed. In the present work, a study based on micro-mechanical models brings new insight to this invariant-based approach. The Rule of Mixtures...
Article
Together with fiber breakage and matrix cracking, delamination is one of the common damage mechanisms occurring in laminated fiber-reinforced composite structures. Delamination initiates due to the relatively low interlaminar strength of adjacent plies. Delamination onset and propagation can be induced by various combinations of loads and usually l...
Article
In order to analyze composite structures under dynamic condition or model manufacturing processes in which high strain rates exist, it is important to develop a constitutive model that regards these effects. In this work, a phenomenological approach is used to formulate a continuum damage for composites in presence of high strain rates. Visco-plast...
Article
An optical experimental procedure for evaluating the J-Integral from full-field displacement fields under dynamic loading is proposed in this work. The methodology is applied to measure the J-integral in the dynamic compressive loading of fiber-reinforced composites and to calculate the dynamic fracture toughness associated with the propagation of...
Article
Full-text available
Single lap bonded joints with four different composite adherend stacking sequences were tested and numerically simulated. The aim was to evaluate the effect of the layups on the quasi-static tensile failure of the bonded joints. The study shows that increasing the adherends bending stiffness postpones the damage initiation in the joint. However, th...
Article
High densities (>10 billion fibers per cm ² ) of aligned carbon nanotubes (A-CNTs) are used to reinforce the interlaminar resin-rich region of aerospace-grade unidirectional carbon microfiber plies in a hierarchical carbon fiber reinforced plastic (CFRP) laminate architecture. Such nano-engineered interfaces have been shown to increase interlaminar...
Article
Full-text available
The mechanical response of IM7-8552 carbon epoxy was investigated for transverse tension and transverse tension/in-plane shear loadings at static and dynamic strain rates using transverse tension and off-axis tension specimens. The dynamic tests were carried out on a split-Hopkinson tension bar at axial strain rates from 113 to 300 s - 1. With the...
Article
This paper describes a new approach for the simulation of lightning-induced damage in carbon fibre-reinforce polymer (CFRP) composite materials. In the past, the lightning-induced damage was mainly described by thermal or thermoelectric approaches. However these approaches need to be supplemented by mechanical pressure/force concepts for describing...
Article
This paper presents an analytical model to predict the stress redistribution around broken fibres in hybrid polymer composites. The model is used under the framework of a progressive failure approach to study the load redistribution around breaks in hybrid composites. The outcomes of the model are validated by comparing it with a spring element mod...
Article
The design of composite structures relies on the accurate determination of design allowables, which are statistically based material parameters that take into account manufacturing, geometrical and microstructure variability. The accurate determination of these design parameters requires extensive experimental testing, which makes the certification...
Article
Short fiber-reinforced thermoplastics show nonlinear response under different sorts of loadings. The nonlinear behavior is referred to the plasticity-induced deformation in the short fiber reinforced materials. Proper constitutive equations are required to describe their mechanical response. These materials are considered transversely-isotropic, wh...
Article
Thick unidirectional fiber reinforced RTM6 epoxy resin specimens were processed by resin transfer molding and tested in transverse compression. Homogenized response from micromechanical analyses on representative volume elements, using a constitutive model for the matrix identified and validated on bulk RTM6 specimens, were assessed towards the exp...
Article
Micromechanics-based fracture criteria for highly cross-linked thermosets are heavily needed in the context of multiscale composite failure analysis. Fracture in an epoxy resin under quasi-static loadings was previously addressed using a two-parameter model, formulated in terms of the attainment of a critical tensile stress at the tip of internal d...
Article
This paper provides an overview of the current approaches to predict damage and failure of composite laminates at the micro-(constituent), meso-(ply), and macro-(structural) levels, and their application to understand the underlying physical phenomena that govern the mechanical response of thin-ply composites. In this context, computational micro-m...
Article
An in-depth analysis of the stress fields that surround a broken fibre in fibre reinforced composites is performed and the effects of different material properties are analysed. The stress fields obtained using a spring element model with a random distribution are compared with analytical formulations present in the literature, within a progressive...
Conference Paper
Full-text available
Bottom-up multi-scale modeling approaches of composites involve a first scale-transition from the constituents at the microscopic scale to the behavior of the yarn and the ply at the mesoscopic scale. In this contribution, finite element (FE) simulations carried out on representative volume elements (RVE) of a unidirectional composite (UD), based o...
Article
Low velocity impact events significantly reduce the mechanical performance of composite structures even though the damage might be barely visible. Numerical simulations can be used to understand and improve the damage resistance and tolerance of composite structures. However, numerical simulations are usually computationally intensive and their app...
Article
Purpose This study aims to achieve a “pseudo-ductile” behaviour in the response of hybrid fibre reinforced composites under uniaxial traction by solving properly formulated optimization problems. Design/methodology/approach The composite material model is based on the combination of different types of fibres (with different failure strains or st...
Article
The enhanced mechanical performance of thin-ply laminates results from their ability to delay the onset of damage typically observed in composite materials. However, in notched structures, subcritical damage growth causes beneficial stress redistributions in the vicinity of the notch, blunting the stress concentration. Precluding these damage mecha...
Article
Thin-ply carbon fiber laminates have exhibited superior mechanical properties and damage resistance when compared to standard thickness plies and enable greater flexibility in laminate design. However, the increased ply count in thin-ply laminates also increases the number of ply-ply interfaces, thereby increasing the number of relatively weak and...
Chapter
This chapter describes the main topics related to the use of cohesive elements in the simulation of delamination in polymer composite materials. The kinematic and constitutive idealizations used in cohesive zone models, as well as the numerical implementation of cohesive zone models in the context of the finite element methods is discussed. Guideli...
Chapter
The concept of Friction Riveting (FricRiveting) is based on the principles of mechanical fastening and friction welding, where joining energy in the form of frictional heat is supplied by the rotational movement of one of the joining partners (normally a cylindrical rivet). This technique allows for the manufacture of joints with high mechanical pe...
Article
Full-text available
An efficient computational model to simulate tensile failure of both hybrid and non-hybrid composite materials is proposed. This model is based on the spring element model, which is extended to a random 2D fibre packing. The proposed model is used to study the local stress fields around a broken fibre as well as the failure process in composite mat...
Chapter
This chapter presents the analysis models, developed at different length scales, for the prediction of inelastic deformation and fracture of polymer composite materials reinforced by unidirectional fibers. Three different length scales are covered. Micro-mechanical models are used to understand in detail the effects of the constituents on the respo...
Article
In this paper, we propose a simple 2D and 3D crack evolution algorithm which avoids the variable/DOF mapping within mesh adaptation algorithms. To this end, a new area/volume minimization algorithm for damaged elements is introduced with the goal of improving the crack path representation. In addition, the new algorithm consists of: (i) mesh-creati...
Article
Advanced non-linear Finite Element models for the strength prediction of composite laminates normally result in long computing times that are not suitable for preliminary sizing and optimisation of structural details. Macro-mechanical analytical models, in spite of providing quick predictions, are based on properties determined from tests performed...
Article
The effect of through-thickness compressive stress on mode II interlaminar fracture toughness is investigated experimentally and replicated numerically. The modified Transverse Crack Tensile specimen recently proposed by the authors is used, together with an experimental device designed to apply a constant transverse compressive stress on the surfa...
Article
This work presents an experimental method to measure the compressive crack resistance curve of fiber-reinforced polymer composites when subjected to dynamic loading. The data reduction couples the concepts of energy release rate, size effect law and R-curve. Double-edge notched specimens of four different sizes are used. Both split-Hopkinson pressu...
Article
The effect of ply thickness on the onset of intralaminar and interlaminar damage is extremely important for the structural response of laminated composite structures. This subject has gained particular interest in recent years due to the introduction in the market of spread-tow, ultra-thin carbon-fibre reinforcements with different configurations....
Article
Full-text available
This paper presents a consistent anisotropic damage model for laminated fiber-reinforced composites relying on the 3D-version of the Puck failure criterion. The current model is based on ply failure mechanisms (fiber and inter-fiber failures) incorporating energetic considerations into the progressive damage evolution. The proposed formulation is i...
Article
Full-text available
Thin ply laminates are a new class of composite materials with great potential for application in the design of thinner and highly optimized components, resulting in potential weight savings and improved mechanical performance. These new composites can stir the development of lighter structures, overcoming current design limitations as well as nota...
Article
The present paper will make a brief review on some of the most relevant through-thickness reinforcement technologies for CFRP/Metal and CFRP/CFRP joints developed so far. A distinction between the traditional (“z-pinning” and “stitching and tufting”) and novel (“COMELDTM”, “CMT”, “HYPER” and “RHEA”) 3D-reinforcement techniques will be made and the...
Article
Advanced non-linear Finite Element models for the strength prediction of composite laminates normally result in long computing times that are not suitable for preliminary sizing and optimisation of structural details. Macro-mechanical analytical models, in spite of providing quick predictions, are based on properties determined from tests performed...
Article
Full-text available
A critical parameter in a hybrid CFRP/steel composites is the shear stress between CFRP plies and steel foils.This paper presents an experimental and numerical research on the single lap shear stress in hybrid CFRP/Steel specimens in accordance with DIN EN ISO 1465. Four different types of specimens were tested: Vacuum basting surface treatment and...
Article
This work focuses on the development of methods to measure the intralaminar fracture toughness of IM7/8552 CFRP at extreme temperatures. The size effect law of scaled double-edge-notched (DEN) specimens is used to obtain the crack resistance curves associated with longitudinal failure of polymer composites. The compressive and tensile crack resista...
Article
This paper focuses on the mechanical characterization of biaxial braided composites under multiaxial stress states. Off-axis experiments in tension and compression were used to introduce multiaxial stresses in the material. The characterization was focused on nonlinear deformation and failure behavior: loading/unloading of the specimen was used to...
Conference Paper
Full-text available
Fiber rotation is an important source of nonlinearity in the fiber-reinforced composites. Fiber rotation increases the stiffness of the material, increases the apparent axial modulus and intra-ply stresses of fiber reinforced materials, while the damage propagation decreases their stiffness. This means that there is a competing effect between fiber...
Article
The authors regret to inform that one of the modifications proposed in the article “High-fidelity micro-scale modeling of the thermo-visco-plastic behavior of carbon fiber polymer matrix composites” [1] was found to be unnecessary: the paraboloid yield criterion is sufficient to describe the shear behavior of the epoxy matrix considered (Epoxy 3501...
Conference Paper
Full-text available
A continuum damage model for the prediction of the onset, evolution of intra-laminar failure mechanisms and the collapse of structures manufactured in fiber-reinforced plastic laminates was proposed by Maimi et al. based on LARC failure criteria. An extended model is proposed to incorporate finite fiber rotation in fiber reinforced plastic laminate...
Conference Paper
Full-text available
Thick RTM-processed unidirectional (UD) samples were produced and tested under transverse compression. The experimental results were confronted to micro-mechanical analyses on representative volume elements (RVEs) with random fiber distributions and periodic boundary conditions. The matrix used is the RTM6 epoxy resin, whose curing cycle was used f...
Article
This work presents an experimental study on the effect of ply-level hybridisation on the tensile unnotched and notched response of composite laminates. In a first assessment, notched tests were performed on laminates with nominal ply thicknesses between 0.03 mm and 0.30 mm. From the understanding of the effect of ply thickness on the damage mechani...
Article
A new fracture criterion for semi brittle epoxy materials is developed, expressed in terms of the attainment of a local critical value of the maximum principal stress at the tip of small internal defects. The criterion is assessed on the highly cross-linked structural epoxy resin RTM6 used as matrix in fiber reinforced composites. The criterion rel...
Article
Full-text available
Three different models with increased complexity to study the effects of hybridization on the tensile failure of hybrid composites are proposed. The first model is a model for dry bundles of fibres based on the statistics of fibre strength. The second is a model for composite materials based on the multiple fragmentation phenomenon. Lastly, a micro...
Article
The present work addresses the damage mechanisms of polymer-based laminated composite materials under different hygrothermal conditions by means of the translaminar fracture toughness using Double Edge Notched Tensile tests of a cross-ply laminate manufactured with T800S/M21 carbon/epoxy material. Three different conditions were considered: as rec...
Article
Full-text available
Hybrid CFRP-steel composites are a very promising solution to increase bolt bearing strength in composite aerospace structures. This paper reports the findings on the static and fatigue tests performed in composite specimens made of CFRP and steel foils and compares these results with conventional CFRP specimens. A servo-hydraulic machine was used...