Strength analysis and failure prediction of glass adhesive joints

This research study seeks to evaluate the load response and failure prediction of glass/steel adhesive joints. The need for sustainable construction materials along with recent architectural trends and technological developments have made glass more accessible than ever before in the construction industry. Limited attempts have been made to compare the performance of bolted and adhesive connections for glass/steel structures, while interface characterisation studies are also lacking. Damage initiation and propagation in the adhesive layer is rarely modelled numerically, and the development of cohesive zone models has been restricted to reference values as hybrid coupon tests are difficult to test successfully. Lastly, while the degradation of glass/steel adhesive joints has been examined experimentally, a numerical tool for the prediction of the performance of the joints after exposure is currently lacking.Benchmark designs of glass/steel bolted and adhesive joints were introduced and tested experimentally in four different load cases. Adhesive joints were found to be stronger and stiffer for all load cases examined. It was also observed that lower strength ductile adhesive (in terms of bulk properties) produced joints with higher failure loads. Numerical analyses showed that ductile adhesives developed a large plastic zone and redistributed the stress concentrations more effectively from the corners of the joints. Therefore, a larger adhesive area was resisting the loading. This understanding of the synergistic property combinations of strength and ductility of the adhesives led to the development of a numerical tool for the optimum selection of adhesives based on the joint design. The identified adhesive led to a significant strength increase for every load case examined.The long term performance of glass/steel adhesive joints was evaluated by exposing the joints to conditions of high temperatures and humidity, and the degradation of the bulk properties and the interfaces was recorded. It was shown that the bulk properties and the interface properties degrade at different rates. The glass/adhesive interface degradation was shown to be more significant and controlled the failure performance of the joints.Numerically, a continuum mechanics and a cohesive zone modelling (CZM) approach were evaluated for their suitability in predicting the failure load of glass/steel adhesive joints before and after environmental exposure. Input parameters for continuum mechanics approaches are based on bulk properties only and are easier to evaluate than CZM interface parameters. An in-house heat strengthening methodology development was necessary to increase the strength of small coupon sized glass substrates for accurate interface characterisation. It was shown in this work that both numerical methods were accurate in predicting the performance of the unaged joints. After environmental exposure, the CZM approach, which allows to account for the more severe interface degradation, performed significantly better. This finding highlights the need for reliable enhanced experimental testing procedures for interface characterization for hybrid glass/steel joints

Prediction of moisture diffusion and failure in glass/steel adhesive joints

Glass/steel adhesive joints are being used increasingly in the construction industry as they offer significant structural advantages over conventional mechanical fastener approaches. However, adhesive joints are also known to be sensitive to moisture diffusion into the bondline, which reduces the interfacial bonding strength for hybrid glass/steel substrates. The effect of moisture on the performance degradation of glass/steel adhesive joints has been successfully predicted assuming adhesive property degradation but requires experimental determination of the affected moisture ingress zone. This study utilizes a multi-physics numerical approach implemented via the commercial finite element code Abaqus 2020, which firstly simulates moisture ingress into the adhesive/glass interface and subsequently couples the diffusion effects with a cohesive zone modelling approach for damage initiation and propagation. The numerical predictions are calibrated against experimental data on glass/steel Double Cantilever Beam (DCB) specimens, which are bonded with a ductile methacrylate adhesive (Araldite 2047–1). The modelling approach is then validated against the experimental response of large double lap shear joints of a significantly different bondline geometry. It is demonstrated that the numerical model successfully predicts the critical exposure time for partial to complete joint degradation enabling the development of engineering guidelines for life-time prediction of various joint geometries.</p

Abstract of: Strength evaluation and failure prediction of bolted and adhesive glass/steel joints

This paper investigates the use of bolted and brittle/ductile adhesive connections in glass structures. Two benchmark designs of shear connections are introduced and tested experimentally in quasi-static tensile tests. The designs consist oftempered glass and aluminium substrates while steel splices are used for the load application. In addition, material characterisation testing for the glass and the adhesive is performed and the outputs are used for the numerical simulation of the same joints. Pressure-sensitive, plasticity and failure models are introduced and calibrated to accurately capture the behaviour of the adhesives. Good agreement between the experimental observations and numerical predictions is achieved. The results show that both types of adhesive joints outperform bolted joints while counter-intuitively the lower strength ductile adhesive achieves consistently higher joint strength compared to the brittle adhesive. The numerical analyses highlight that while brittle adhesive joints fail once the fracture strain of the adhesive has been reached, while for ductile adhesives an extensive plastic zone develops near the areas of stress concentrations thereby delaying the damage initiation

Spreading of memes on multiplex networks

A model for the spreading of online information or ‘memes’ on multiplex networks is introduced and analyzed using branching-process methods. The model generalizes that of (Gleeson et al 2016 Phys. Rev.X) in two ways. First, even for a monoplex (single-layer) network, the model is defined for any specific network defined by its adjacency matrix, instead of being restricted to an ensemble of random networks. Second, a multiplex version of the model is introduced to capture the behavior of users who post information from one social media platform to another. In both cases the branching process analysis demonstrates that the dynamical system is, in the limit of low innovation, poised near a critical point, which is known to lead to heavy-tailed distributions of meme popularity similar to those observed in empirical data

Mechanical and interfacial characterisation of leading-edge protection materials for wind turbine blade applications

Modern wind turbine blades experience tip speeds that can exceed 110 m/s. At such speeds, water droplet impacts can cause erosion of the leading edge, which can have a detrimental effect on the performance of the wind turbine blade. More specifically, rain erosion is leading to both reduced efficiency and increased repair costs. The industry is using polymeric coatings—leading-edge protection (LEP) materials—to protect the blades but those are also prone to rain erosion. In this work, LEP materials that are currently used by the industry for the protection of wind turbine blades were selected and their performance assessed. The LEP materials were characterised in terms of mechanical properties by using different experimental methods, and they were also assessed in terms of durability by performing rain erosion testing (RET). Finally, the damage and failure mechanisms observed were further investigated using CT scanning. This paper provides an insight to the properties of LEP materials, their durability, and the damage and failure mechanisms they experienced during rain erosion.</p

Multilayer Leading Edge Protection systems of Wind Turbine Blades: A review of material technology and damage modelling

In the immediate future, wind power will provide more electricity than any other technology based on renewable and low-emission energy sources. As a result, the size of offshore wind turbines has increased to harvest more wind energy in order to achieve the 2050 EU carbon neutral targets. The use of composites opens great prospects in the design and manufacture of the wind turbine blades due to their optimization versatility but composites perform poorly under impact and are sensitive to environmental factors. To combat this, blade manufacturers employ polymer-based surface coatings, caps or tapes to protect the composite structure. However, it is the repeated impact of rain droplets combined with the high blade tip speed, which are mostly contributing to the erosion of wind turbine blades [1]. The hindering of leading-edge erosion could be obtained through its multilayer material optimization i.e. Leading Edge Protection LEP [2]. Both the surface erosion and the intra-layer adhesion are affected by the shock wave propagation through the thickness of the LEP system produced from the collapsing water droplet after impact [3]. It is necessary to increase the interfacial fracture toughness resistance of the multy-layered system from the surface to the interface boundaries to damp the surface damage and avoid subsurface delamination [4]. Therefore, validated models considering the developed multicomplex stress states and the material degradation due to environmental loads are required for design purposes toward anti-erosion protection performance. This investigation summarizes the review of the current literature conducted in the framework of the IEA Wind TCP (International Energy Agency Wind Technology Collaboration Programme) - Task 46 Erosion of wind turbine blades [5]. It focuses on two main issues: firstly, the LEP material configuration used in industry considering the blade integration technology and, secondly, the modelling techniques and numerical procedures currently used to predict both wear surface damage and interface delamination failure. This work will allow for the identification of gaps within the research that can be explored during IEA Wind Task 46

Multilayer Leading Edge Protection systems of Wind Turbine Blades: A review of material technology and damage modelling

In the immediate future, wind power will provide more electricity than any other technology based on renewable and low-emission energy sources. As a result, the size of offshore wind turbines has increased to harvest more wind energy in order to achieve the 2050 EU carbon neutral targets. The use of composites opens great prospects in the design and manufacture of the wind turbine blades due to their optimization versatility but composites perform poorly under impact and are sensitive to environmental factors. To combat this, blade manufacturers employ polymer-based surface coatings, caps or tapes to protect the composite structure. However, it is the repeated impact of rain droplets combined with the high blade tip speed, which are mostly contributing to the erosion of wind turbine blades [1]. The hindering of leading-edge erosion could be obtained through its multilayer material optimization i.e. Leading Edge Protection LEP [2]. Both the surface erosion and the intra-layer adhesion are affected by the shock wave propagation through the thickness of the LEP system produced from the collapsing water droplet after impact [3]. It is necessary to increase the interfacial fracture toughness resistance of the multy-layered system from the surface to the interface boundaries to damp the surface damage and avoid subsurface delamination [4]. Therefore, validated models considering the developed multicomplex stress states and the material degradation due to environmental loads are required for design purposes toward anti-erosion protection performance. This investigation summarizes the review of the current literature conducted in the framework of the IEA Wind TCP (International Energy Agency Wind Technology Collaboration Programme) - Task 46 Erosion of wind turbine blades [5]. It focuses on two main issues: firstly, the LEP material configuration used in industry considering the blade integration technology and, secondly, the modelling techniques and numerical procedures currently used to predict both wear surface damage and interface delamination failure. This work will allow for the identification of gaps within the research that can be explored during IEA Wind Task 46.Aerospace Manufacturing Technologie