Sofia Teixeira de Freitas

Sofia Teixeira de Freitas
Delft University of Technology | TU · Aerospace Structures and Materials (ASM)

PhD

About

75
Publications
30,686
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
965
Citations

Publications

Publications (75)
Article
Full-text available
For full-document (open-access): http://www.appliedadhesionscience.com/content/pdf/s40563-015-0033-5.pdf This paper introduces a new type of peel tests dedicated to composite bonding: Composite Peel Tests. This test is inspired on the standard floating roller peel test widely used for metal bonding. The aim of this study is to investigate the pote...
Article
Full-text available
In this research, the adhesion properties of bonded composite-to-aluminium joints are evaluated using floating roller peel tests. Tests were performed using two different adhesives and different adherend lay-ups: composite-to-aluminium, composite-to-composite and aluminium-to-aluminium. The results show that floating roller peel tests, widely used...
Article
Full-text available
Two systems for reinforcing "in-service" orthotropic bridge decks (OBDs) have been researched: the bonded steel plates system and the sandwich steel plates system. The main idea of these types of reinforcements is to stiffen the existing deck plate, thereby reducing the stress at the fatigue-sensitive details, and thus extending the fatigue life of...
Article
Full-text available
Orthotropic steel bridges have experienced early fatigue cracks at several welded connections in the steel deck plate. One of the possible strengthening systems to enlarge the fatigue life of the existing decks consists of bonding a second steel plate to the existing deck. This renovation technique was for the first time applied on the orthotropic...
Article
In some industrial applications, adhesive joints are cyclically exposed to a moist environment, where cyclic moisture absorption and desorption can significantly alter the fracture energy of the bonded joints. Most previous studies are based on monotonic aging conditions, while the performance of bonded joints under cyclic aging is not well explore...
Article
The adhesive layer in the adhesive joints can experience different modes of loading. Although the fracture energy of adhesive is generally considered to be a material parameter, it is found to be a function of the joint configuration too. Thus, to accurately simulate the behaviour of bonded joints, it is recommended to obtain the fracture energy of...
Article
Full-text available
Thicker bondlines along with manufacturing-tolerant and fracture-resistant adhesives are trends visible across different industries, especially maritime. In this work, two contrasting adhesives: an elastic-brittle epoxy-based, and a nonlinear-ductile methyl methacrylate (MMA) are characterized and compared via tensile, compact tension (CT) and doub...
Article
Full-text available
Three-point bending analysis, experimental and numerical, is conducted for three different sizes, 30*30 mm, 40*40 mm and 60*60 mm, of one-sided square cross-ply TEXIPREG HS 160 RM carbon-fiber-reinforced polymer (CFRP) patches as well as intact and notched specimens. The tests are carried out with the aim to study the influence of the patch’s size...
Article
Full-text available
The aim of this research was to investigate the self-healing potential of damaged Al joints when bonded using novel eco-epoxide adhesives derived from tannic acid (TA). Two eco-epoxy components based on TA, (A) glycidyl ether and (B) glycidyl phosphate ester of TA, were produced. The effect of the eco-epoxy components on the self-healing ability wa...
Article
The aim of this paper is to study the self-healing capability of fractured Al joints bonded with novel eco-epoxide adhesives synthesized from a bio-renewable raw material (tannic acid – TA). Two synthesized eco-epoxy components based on TA, (A) glycidyl ether and (B) glycidyl phosphate ester of TA, were used as a replacement for the toxic epoxy com...
Article
Full-text available
The goal of this paper is to evaluate the strain-based partitioning method (SBM), an analytical method based on beam analysis, for the mixed-mode fracture characterization of asymmetric cracks. The fracture energy is calculated at the crack tip of mixed-mode bending (MMB) test with asymmetric geometry and asymmetric material parameters. The fractur...
Article
Full-text available
The development of new adhesives has allowed to expand the application of bonding into the most diverse industrial fields. This review article presents the commonly used experimental methods for the investigation of mechanical performance of adhesively bonded joints in the aerospace, wind energy, automotive and civil engineering sectors. In these s...
Article
Full-text available
This work investigates the effect of long-term environmental exposure on the performance of composite-to-metal bonded joints. Specimens are manufactured using a carbon-fiber reinforced polymer (CFRP) co-bonded to a steel member with epoxy adhesive and aged in a salt spray chamber. The mixed-mode fracture behavior of the non-aged and aged specimens...
Article
Adhesive bonding is one of the most suitable joining technologies in terms of weight and mechanical performance for current carbon fiber reinforced polymer aircraft fuselage structures. However, traditional joint topologies such as single overlap joints induce high peel stresses, resulting in sudden failure and low joint strength when compared to m...
Article
This paper addresses the sensitivity of the ultrasonic welding process for joining dissimilar composites to variations in either the welding force or amplitude of vibrations. For that, carbon fibre (CF)/ epoxy specimens were welded to CF/ polyetheretherketone (PEEK) specimens, through a polyetheretherimide (PEI) coupling layer co-cured with the CF/...
Article
Full-text available
This study is devoted to the use of acoustic emission technique for a comprehensive damage assessment, that is, damage detection, localization, and classification, of an aeronautical metal-to-composite bonded panel. The structure comprised a titanium panel adhesively bonded to carbon fiber-reinforced plastic omega stringers. The panel contained a s...
Article
Full-text available
This study investigates the fracture onset and crack deflection in multi-material adhesive joints with thick bond-lines (≈10 mm) under global mode I loading. The role of adherend-adhesive modulus-mismatch and pre-crack length are scrutinized. The parameters controlling the crack path directional stability are also discussed. Single-material (i.e. s...
Article
Full-text available
Two synthesized eco-epoxy components based on TA: (A) glycidyl ether and (B) glycidyl phosphate ester, are used, as a replacement for the Bisphenol A (BPA) based epoxy component, for bonding aluminum (Al) and carbon fiber reinforced polymer (CFRP). Their effect on the mode I fracture toughness (GI) is evaluated by Double Cantilever Beam (DCB) testi...
Article
Full-text available
This study aims at assessing the sensitivity of the ultrasonic welding process for joining epoxy- to thermoplastic-based composites sensitivity to the heating time. For that, carbon fibre (CF)/epoxy adherends with a co-cured PEI coupling layer were ultrasonically welded to CF/polyetheretherketone (PEEK) adherends at different heating times. Process...
Article
Nowadays, dissimilar adhesive joints are used widely in different industrial sectors. For this type of joints, the investigation of the fracture behaviour under pure mode I loading is a vital issue. In order to study mode I fracture parameters of adhesive joints, scientists have proposed standard double cantilever beam (DCB) specimens. In dissimila...
Conference Paper
Full-text available
The development of composite materials technology introduces innovative structural applications. In offshore industry, composite repairs are applied to the rehabilitation of metal structures, resulting in a bi-material bonded structure between composite and metal parts. In this work, the mechanical behavior of composite-to-metal bonded joints is ev...
Article
Full-text available
Using adhesives for connection technology has many benefits. It is cost-efficient, fast, and allows homogeneous stress distribution between the bonded surfaces. This paper gives an overview on the current state of knowledge regarding the technologically important area of adhesive materials, as well as on emergent related technologies. It is expecte...
Article
Full-text available
High performance structures require the use of different materials to meet their demanding requirements. Especially fibre reinforced polymer composites are nowadays often bonded to metals in order to take the most advantage of the materials properties and to minimize their disadvantages. However, the interface in such bi-material assemblies often r...
Article
Full-text available
In this work, the influence of a layer of glass fiber mat (GFM) inserted in a bi-material bonded joint interface is investigated as a toughening mechanism to improve the fracture performance of bonded structures. Composite-to-metal bonded specimens were manufactured by hand lay-up using two different consolidation processes: at room pressure or usi...
Article
Full-text available
The goal of this study is to explore new topologies for adhesively bonded composite overlap joints in order to improve their strength under tensile loading. Multiple stacked overlaps, also referred as finger joints, are compared with single overlap topologies. The quasi-static tensile behaviour of single lap joints with two overlap lengths 12.7 mm...
Article
Full-text available
A high-power UV-irradiation technique was proposed for the surface treatment of PPS and PEEK composites,aiming to achieve good adhesion with epoxy adhesives. The composite substrates were rapidly UV-irradiatedfor a duration of between 2–30s, and then bonded using an aerospace film adhesive to produce joints. Tensilelap-shear strength and mode-I and...
Article
Full-text available
This paper presents a new process for obtaining eco-epoxide adhesives synthesized from bio-renewable raw material (tannic acid-TA) and used for bonding lightweight materials (aluminum (Al) and carbon fiber reinforced polymer (CFRP)). Two synthesized bio-epoxy components based on TA, (A) glycidyl ether and (B) glycidyl phosphate ester of TA, were us...
Article
Full-text available
This study investigates the early fatigue damage of cross-ply carbon/epoxy laminates. The aim is to unfold the damage accumulation process, understand the interaction between different damage mechanisms, and quantify their contribution to stiffness degradation. Tension-tension fatigue tests were performed, while edge observation and DIC technique m...
Article
Full-text available
A high-power UV-irradiation technique was proposed for the surface treatment of PPS and PEEK composites, aiming to achieve good adhesion with epoxy adhesives. The composite substrates were rapidly UV-irradiated for a duration of between 2-30 s, and then bonded using an aerospace film adhesive to produce joints. Tensile lap-shear strength and mode-I...
Article
Full-text available
The aim of this study is to investigate the effect of the adherend material on the mode I fracture behaviour of bi-material composite bonded joints. Both single-material (steel-steel and composite-composite) and bi-material (steel-composite) joints bonded with a structural epoxy adhesive are studied. Additionally, two adhesive bondline thicknesses...
Article
Full-text available
Ultrasonic welding is a highly promising technique for joining thermoplastic to thermoset composites. A neat thermoplastic coupling layer is co-cured on the surface to be welded to make the thermoset composite ‘weldable’. A reliable bond is attained when miscible thermoplastic and thermoset materials are chosen. For welding carbon fibre/polyetheret...
Article
Full-text available
This study is devoted to the damage characterization of Non-Crimp Fabric (NCF), 2D plain-woven (2D-PW) and 3D orthogonal plain-woven (ORT-PW) carbon/epoxy laminates, subjected to compression after multiple-impact loading, using Acoustic Emission (AE). The ultrasonic C-scan images showed that the interlaminar damage area induced by the single and 3-...
Article
Full-text available
Mechanics of double-lap Steel-to-CFRP adhesively-bonded joints loaded in tension are investigated experimentally using Digital Image Correlation (DIC) and Acoustic Emission (AE), analytically using a one-dimensional closed-form solution and numerically with Finite Element analysis. The double-lap bi-material joints are fabricated of a steel core ad...
Article
In ultrasonic welding of thermoplastic composites an energy director (ED) (i.e. neat thermoplastic film), is used between the two adherends to be welded, to promote frictional and viscoelastic heating. For welding of thermoset composites (TSC), a thermoplastic coupling layer is co-cured on the surface to be welded as typical procedure to make the T...
Article
The aim of the present study is to characterize the damage in bi-material steel-to-composite double-lap adhesively-bonded joints using Acoustic Emission (AE). Two different structural adhesives, a ductile (Methacrylate-based) and brittle (Epoxy-based), were used to bond CFRP skins to a steel core. The fabricated joints were loaded in tension while...
Article
This paper investigates the effect of the fabric architecture and the z-binding yarns on the compression after multiple impacts behavior of composites. Four fiber architectures are investigated: non-crimp fabric (NCF), 2D plain weave (2D-PW), 3D orthogonal plain (ORT-PW) and twill (ORT-TW) weave. The specimens were subjected to single and multiple...
Article
The fracture behaviour of joints bonded with a structural epoxy adhesive and bond line thicknesses of 0.1–4.5 mm has been studied. However, limited research is found on similar joints with thicker bond lines, which are relevant for maritime applications. Therefore, the effect of the adhesive bond line thickness, varying from 0.4 to 10.1 mm, on the...
Conference Paper
Full-text available
The dissemination of composite materials introduces applications of hybrid structures with composite and metal parts. The development of reliable methodologies to evaluate the performance of these structures is required. In this work, the mixed-mode fracture behavior of a bi-material adhesively bonded joint is investigated. A new strain-based equiv...
Article
This work is intended to characterize the mechanical behavior of hybrid carbon–glass composite plates under combined loading of bending and torsion, and to determine the optimal ply fiber orientations to minimize the maximum out-of-plane displacement under such loading conditions. Hybrid composite plates were manufactured with 10 plies each and dif...
Article
The aim of this research is to study the influence of moisture absorption at low moisture contents on the creep behaviour of an epoxy adhesive in steel bonded joints. Single lap joints were manufactured using high strength steel adherends and a two-component epoxy adhesive. The single lap joints were tested at load levels corresponding to average l...
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
Full-text available
The dissemination of composite materials introduces applications of hybrid structures with composite and metal parts. The development of reliable methodologies to evaluate the performance of these structures is required. In this work, the mixed-mode fracture behaviour of a bi-material adhesively bonded joint is investigated. A new strain-based crit...
Article
Full-text available
An essential question to predict the structural integrity of bi-material bonded joints is how to obtain their fracture properties under pure mode I. From open literature, it is found that the most commonly used design criterion to test mode I fracture is matching the flexural stiffnesses of the two adherents in a DCB coupon. However, the material a...
Conference Paper
Risk prioritization is an important procedure in FMEA methodology where failure modes are prioritized using the so-called risk priority number (RPN), which prioritizes failure modes based in only three risk variables usually, severity, occurrence, and detectability. However, in some risk scenarios, more than three risk variables can improve risk pr...
Conference Paper
Full-text available
The goal of this study is to investigate new topologies of composite bonded joints in order to improve their strength under tensile loading. Multiple stacked overlaps are compared with single overlap designs. The concept of multiple stacking is well known as ply-interleaving technique for co-curing dissimilar materials. For a secondary bonding proc...
Conference Paper
Full-text available
Adhesive bonding is a highly desirable joining technique to join composites to metals. The surfaces of both composite and metal substrates have to be carefully treated before bonding them together, in order to avoid interface failure between the adherend's surface and adhesive. This paper describes the surface pretreatments on carbon fiber reinforc...
Article
Full-text available
Steel-to-glass laminated connections, which have recently been developed, limit stress intensifications on the glass and combine strength and transparency. Transparent Structural Silicone Adhesive (TSSA) connections have been used in several projects worldwide; however, the hyperelastic and viscoelastic nature of the material has to date not been f...
Article
Full-text available
The aim of this study is to assess the interlaminar adhesion of carbon-epoxy laminates under salt water condition. Carbon-epoxy laminate specimens were immersed in a salt water tank for 60 days. Some specimens were then dried at room temperature for 280 days, until recovering their initial weight. Specimens were tested using the composite peel test...
Article
This paper addresses the fracture behaviour of bonded composite plates featuring a kissing bond along the crack growth path. Double cantilever beam (DCB) experiments are carried out under a displacement controlled loading condition to acquire the load response. The experimental data are collected and analysed analytically for specimens with and wit...
Article
Full-text available
Adhesive bonding is one of the most promising joining technologies for composite aircraft. However, to comply with current aircraft certification rules, current safety-critical bonded joints, in which at least one of the interfaces requires additional surface preparation, are always used in combination with redundant mechanical fasteners, such as r...
Article
Full-text available
In this work, an experimental study has been carried out to evaluate the effect of salt water condition on the long-term adhesion of composite-to-metal bonded joints using peel tests. A new test configuration is tested via fully and partially immersed specimens with 500 mm length. Fracture surfaces of non-aged samples exhibited a cohesive failure w...
Article
Full-text available
Full-scale fatigue tests were performed on two retrofitted orthotropic bridge decks (OBDs). The retrofitting systems consist of adding a second steel plate on the top of the existing deck. The aim is to reduce the stresses at the fatigue-sensitive details and therefore extend the fatigue life of the OBD by stiffening the existing deck plate. Two re...
Article
Full-text available
Full-scale fatigue tests were performed on two retrofitted orthotropic bridge decks (OBDs). The retrofitting systems consist of adding a second steel plate on the top of the existing deck. The aim is to reduce the stresses at the fatigue-sensitive details and therefore extend the fatigue life of the OBD by stiffening the existing deck plate. Two re...
Article
Full-text available
Autoclave manufacturing of fibre metal laminates, such as GLARE, is an expensive process. Therefore, there is an increasing interest to find cost-effective out-of-autoclave manufacturing processes without diminishing the laminate quality. The aim of this study is to evaluate the quality of fibre metal laminate panels adhesively bonded and cured usi...
Article
The curing behaviour and the mechanical behaviour of susceptor-assisted induction-cured adhesively bonded joints has been investigated. Induction Heating (IH) was established by mixing Iron particles into a two component epoxy paste adhesive. The effect of different process parameters, such as particle content, coupling distance and coil current, o...
Article
The aim of this research is to analyse the failure of a Fiber Metal Laminate (FML) skin adhesively bonded to a Carbon Fiber Reinforced Polymer (CFRP) stiffener, under quasi-static loading at different environmental temperatures ( , Room Temperature RT and ) and under fatigue loading at RT. This bonded joint was tested using stiffener pull-off tests...
Article
An experimental study has been carried out to assess the adhesion quality of composite-to-metal bonded joints under salt spray ageing conditions. The tests were performed according to the ASTM standard of floating roller peel tests with a new specimen layup. The layup and geometry of the specimen was defined in order to have the Carbon Fiber Reinfo...