Pull-out behavior of CFRP ground anchors with two-strap ends

Pull-out experiments were performed on three carbon fiber-reinforced polymer (CFRP) ground anchors simulating their applications in different rock types which provided different confinement levels. The CFRP tendons comprised, on the ground side, a prefabricated conical anchor body of high-strength grout in which two CFRP straps were embedded. The anchors reached an average load-bearing capacity of 1384 kN with final failure occurring in the CFRP straps. Grout failure was successfully prevented by an adequate grout selection and installation of CFRP confinement rings to balance spreading forces at the strap ends. The confinement level provided by the surrounding media influenced the activation of the CFRP components in the anchor body by influencing the friction at the CFRP/grout interfaces

The statistical variability and length effects in the tensile transverse behavior of clear timber

In this work, clear timber specimens of different lengths with a small cross-sectional area were cut in the transverse direction of timber boards and tested under tensile loading. Regularly positioned and randomly positioned specimens were cut from different timber boards. Local deformations in each specimen were measured during the tests and the mechanical behavior of specimens of different lengths was compared. Statistics and size effects concerning the elastic modulus and strength were studied. The transverse tensile behavior was approximately linear. The results show very significant variability in the transverse elastic modulus, as high as 1000% between some specimens. The transverse tensile strength decreases linearly with specimen length increase on logarithmic scales

Testing mechanical performance of adhesively bonded composite joints in engineering applications: an overview

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 sectors, due to their excellent intrinsic properties, composite materials are often used along with conventional materials such as steel, concrete and aluminium. In this context, and due to the limitations that the traditional joining techniques present, adhesive joints are an excellent alternative. However, standardized experimental procedures are not always applicable for testing representative adhesive joints in these industries. Lack of relevant regulations across the different fields is often overcome by the academia and companies’ own regulations and standards. Additional costs are thus mitigated to the industrial sectors in relation with the certification process which effectively can deprive even the biggest companies from promoting adhesive bonding. To ensure continuous growth of the adhesive bonding field the new international standards, focusing on actual adhesive joints’ performance rather than on specific application of adhesive joints are necessary.This work was supported by the European Cooperation in Science and Technology [CA 18120]

Fatigue life prediction of wind turbine blade composite materials

Fatigue life prediction of wind turbine rotor blades is a very challenging task, as blade failure is led by different failure types that act synergistically. Inherent defects like wrinkles, fiber misalignments and voids, that can be introduced during fabrication, can constitute potential damage initiation points and rapidly develop to failure mechanisms like matrix cracking, transverse-ply cracking, interface cracking, debonding, fiber breakage, etc. Different methods have been established to address this problem, some based on phenomenological and others on actual damage mechanics modeling. This chapter aims to provide an overview of fatigue life modeling and prediction methodologies for the composite materials and structural composite elements that compose a wind turbine rotor blade under complex loading condition

Review of fatigue of bulk structural adhesives and thick adhesive joints

Fatigue of structural adhesives has been investigated through joints and a little number of works investigate bulk adhesive behaviour itself. Aerospace and automotive engineering focuses more on joint configuration studies, which are correlated with practical applications. Previous works showed that for thin adhesive joints, material properties measured by bulk adhesive testing and joint testing are similar despite the triaxial stress states developing in the adhesive bondlines. However, with the introduction of structural adhesives in construction industry, thicker bondlines have emerged where the bulk adhesive material dominates the joint behaviour. This review work summarises works on the fatigue of bulk structural adhesives used mainly in the construction industry investigating structural adhesives fatigue behaviour either through experiment on joints or on bulk adhesive specimens. The work focuses on thick adhesive bondlines in joints, and discusses the controversy that is over whether adhesive properties from joints or from bulk material should be used

Fatigue dataset of hybrid non-toughened and toughened epoxy adhesives

In this article, four different structural epoxy adhesives such as SPABOND™ 820HTA (non-toughened), SPABOND™ 840HTA (toughened) adhesives, and their two hybrid combinations are fabricated using a manual mixing method. Quasi-static tensile experiments are conducted at standardized and high strain rates using ASTM D638-22 Type II specimens to investigate the strain rate effects on the tensile properties. Tensile-tensile fatigue experiments are performed using ASTM D638-22 Type I and Type II specimens to evaluate the impact of specimen geometry and toughening on fatigue life. The digital image correlation technique is utilized to obtain full-field strain data in these experiments. Technical data analysis, plotting, smoothing, filtering, and averaging are carried out using Origin ProⓇ and MATLAB R2021bⓇ. The obtained S-N curve data can be used to develop fatigue failure criteria and predict the behavior of wind turbine blade adhesive joints through finite element modeling

Dataset for the hybrid non-toughened and toughened epoxy adhesive properties

In this article, the manufacturing and toughening effects on the material properties of epoxy adhesives used in wind turbine rotor blades are presented. Different adhesive materials are developed by combining SPABOND™ 820HTA (non-toughened) and SPABOND™ 840HTA (toughened) adhesives with the machine and manual mixing methods. Firstly, the manufacturing quality are compared between the two methods, in terms of void percentage and void volume using micro-computed tomography. Dynamical Mechanical analysis, uniaxial tensile testing, V-notch shear testing and single-edge-notch beam testing are carried out to evaluate the manufacturing and toughening effects. In these experiments, the digital image correlation technique is exploited to obtain the displacement and strain data. Origin ProⓇ and MATLAB R2021bⓇ are utilized for technical data analysis, plotting, smoothing, filtering, and averaging. The obtained data could be used to select the adhesive material based on the strength and stiffness requirements, develop failure criteria, and predict the thick adhesive joint behavior by finite element modeling

Manufacturing and toughening effects on the material properties of wind turbine blade adhesives

Hybrid adhesives can be developed using commercially available adhesive materials and customized to the required loading conditions. In this paper, SPABONDTM 820HTA (non-toughened) and SPABONDTM 840HTA (toughened) adhesives are hybridized by two strategies and fabricated by machine and manual mixing methods. The manufacturing and hybridization effects on the bulk adhesive properties are evaluated by dynamic me-chanical analysis, quasi-static tensile, V-notch shear and single-edge-notch bending tests. X-ray micro-computed tomography, digital image correlation technique, high speed camera and scanning electron microscopic images are used for assessing the manufacturing quality, computing the full-field displacement and strain, and failure analysis. By considering the manufacturing methods, the measured properties are less influenced by the presence of voids but dependent on the glass fiber filler orientation. The adhesive toughening method improves the strain to failure and tensile toughness, decreases the strength and modulus and no significant effect on the glass transition temperature