Abstract

Abstract

Abstract

The New Zealand Building Code is unique in the world in requiring evidence of a minimum durability of 50 years for all structural building elements. This prescriptive durability requirement equally applies to the adhesives used in structural applications such as engineered wood products (EWPs), including glulam, CLT and LVL. Conventional resorcinol-based structural adhesives have a long history of use in New Zealand, providing evidence of their ability to meet stringent durability requirements. Structural adhesives based on polyurethanes (PURs) are used extensively in other parts of the world and are rapidly gaining increasing interest in New Zealand due to their perceived environmental and production advantages. However, without a sufficiently long history of use, and a lack of data around their performance in the preservative treated pine EWPs typically manufactured in New Zealand, it is difficult to provide evidence of long-term durability for PURs in our domestic building industry. In this work, attenuated total reflectance Fourier transform infrared (ATR FTIR) spectroscopy in conjunction with multi-component analysis (chemometrics) was used to understand the changes that accelerated ageing cause in the chemistry of five PUR-based adhesives. The effect of hygrothermal stress was investigated through exposure of samples to accelerated ageing cycles of varying temperatures and humidities for up to 3 years’ duration. Different samples were affected to different extents by each cycle. Spectroscopic data were also used to build predictive models which have the potential to be used in long-term durability assessment. Spectroscopic investigation in conjunction with mechanical testing offers the opportunity to provide a robust, fit-for-purpose test methodology for assessing the long-term durability of PUR-based structural adhesives.

Abstract

Finite element modelling of adhesive joints has been analysed in this work, applying the results and conclusions of the design process of a multi-material base of an elevator. The main approach of the study has been the modelling of the adhesive joint, different parameters and its application in complex models. For that purpose, a case study has been carried out in a simply supported plate model. Several modelling techniques have been analysed and design recommendations have been proposed. Characterization of composite materials and adhesives has also been studied, given the fact that the anisotropy of the composites is an additional difficulty in the Finite Element Analysis. Having the real properties of these materials is a very important factor for efectiveness in terms of economical and computational cost. The correlation of simulation and experimental results has been analysed in the practical case study and the contribution of the adhesive modelling has been studied. To conclude, the importance of the material characterization and the sensitiveness to the variation of their properties are to be mentioned. The work offers the designer several recommendations on adhesive joint modelling as well as parameters that might affect the analysis of a structure that contains adhesive bonding.

Abstract

One of the main "drivers" in the development of aeronautical structures in composite material is the development of more integrated structures that are manufactured in a single step ("One-Shot") to optimize times. The adhesive materials in film format are one of the main variables to take into consideration to achieve the aforementioned integration. This need has promoted creativity at the level of use / parameterization of new adhesives in the form of a film.

Film adhesives are used in the integration of composite, sandwich or monolithic structures. Regarding sandwich structures, the adhesive film is used to ensure a good adhesion between the core and the prepreg, through the formation of a meniscus of adhesive material in the core cell. This function is fulfilled depending on the type of "carrier". For Monolithic structures, the adhesive film is used to ensure a good adhesion in co-bonding processes (bonding of cured laminate with fresh prepreg) and secondary bonding (bonding between 2 previously cured laminates), interleaved between materials to achieve optimum thickness, guaranteeing the best mechanical properties of the element at interlaminar level. This, without forgetting, the repair processes that are within the processes of co-bonding, with all its specificities and operational limitations, either in manufacturing or in service.

The market options, qualified by OEMs or not, are wide, having developed different support materials, or variants of the same material, with the aim of achieving the best mechanical properties of the elements where they are used.

Abstract

This study experimentally analyses the phenomenon of delamination under static and fatigue loading in mode II using the standardized End-Notched Flexure (ENF) test. Adhesive joints made of two epoxy matrix laminates reinforced with unidirectional carbon fiber are studied, bonded with an epoxy adhesive, and subjected to environmental degradation in a saline environment for exposure periods of 1, 2, 4, and 12 weeks.

By conducting initial static tests on the joints, we identified crucial values for the rate at which energy is released under mode II conditions. These values served as a benchmark to establish the approach for dynamic fatigue testing. Our objective was to generate characteristic curves that illustrate how these adhesive joints behave when fatigue delamination begins, while also assessing the impact of varying exposure periods on their performance. To enhance result interpretation, we employed a probabilistic model rooted in the Weibull distribution to analyse the experimental data.

The results show that adhesive joints experience a decrease in their delamination resistance when exposed to a saline environment.