The mechanical behavior of adhesives is strongly influenced by a large number of variables, relating to a complex interaction of mechanical-physical-chemical factors, such as its loading direction (shear, peel), the temperature and the environmental relative humidity (RH). These variables can have a large influence on the durability of restored art objects where thermoplastic adhesives have been used as a consolidant. This study aims to characterise the mechanical and physical behavior of some adhesives commonly used polymers by conservators as consolidants to restore cultural objects such as canvas paintings or historic wooden furniture. Twelve commercially available natural and synthetic adhesive materials were tested. The influence of RH at room temperature on the mechanical and physical properties of the adhesives was investigated. Shear and peel experiments were performed on adhesively bonded wood and canvas coupon to establish mechanical characterisation. The physical properties of the adhesives were determined by performing moisture adsorption measurements and Differential Scanning Calorimetry (DSC). The results of this study demonstrate that synthetic adhesive products are able to resist higher shear and peel loads than natural types. Moreover, the influence of important changes in RH on the mechanical properties of the adhesives was demonstrated. Reflecting on the combined data derived from shear and peel tests with the adhesive's sensitivity to moisture will help conservators to select the most suitable adhesives for their applications to achieve optimal durability and the best mechanical performance in versatile environmental conditions.

@en

Gelatins are proteinaceous natural materials that are widely used in areas such as conservation and restoration of artifacts as adhesives and consolidants, in pharmaceutics as drug delivery carriers, and in the food industry as structurants. Herein, type A porcine gelatin adhesive films are prepared via solution casting method and their physical and mechanical properties are investigated using X-ray diffraction (XRD), differential scanning calorimetry, contact angle measurement, dynamic mechanical analysis, and uniaxial tensile tests. The results demonstrate a linear correlation between microstructure of gelatin films in terms of their triple-helix content and their macroscopic mechanical properties such as tensile strength and gel (Bloom) strength. Moreover, the findings of this study can help the scientists, in, e.g., art conservation and restoration, to predict the mechanical performance of these adhesives by performing a less material demanding and nondestructive physical measurement such as XRD.

@en

The structural conservation of canvas paintings may require lining, a process in which a secondary canvas is adhered to the reverse of the damaged original canvas to provide additional support. Choosing the optimum adhesive or canvas for lining is challenging. Comprehensive data on thermal and mechanical behaviour of different adhesives to enable the conservator to make informed choices for their treatment purposes is scarce. Hence, in this study, four prevalently used adhesives for lining are chosen and their thermal and mechanical behaviour, such as the glass transition and melting temperatures, static lap shear strength and creep resistance, are compared. Thermal properties of the different adhesives are characterised using differential scanning calorimetry (DSC). Furthermore, the effect of temperature cycles (25, 35, and 45°C at a fixed relative humidity of 48%) on the creep behaviour of lined canvases is evaluated. Lap shear and creep experiments are performed on lined canvas mock-ups. The four adhesives tested are: studio formulations of an animal glue-wheat flour paste, as well as a beeswax-damar resin mixture; a patented formula based on an ethylene vinyl acetate copolymer mixture (BEVA 371 O.F.™); and a mixture of two industrially produced acrylic copolymers (Plextol™ D541 and K360). The results demonstrate the remarkable effect of temperature on the creep behaviour of lined canvases, which can be related to their thermal stability.

@en

The structural preservation of panel paintings and decorated furniture as significant parts of Dutch cultural heritage, requires comprehensive knowledge on the long term behaviour of their constituent materials namely wood and animal glues. A decorated cabinet crafted by Jan van Mekeren (1684-1744) is chosen as the case study. The environment-induced ageing of wooden artefacts is often due to failure of the glue joints between the wooden parts. This behaviour is largely not understood. @en

Rotational acceleration of the head is known to be the cause of traumatic brain injuries. It was hypothesized that by introducing anisotropy in a foam liner in head protection applications, for example, protective helmets, rotational acceleration transmitted to the head can be further mitigated. Therefore, composite foam with a cylinder/matrix configuration with anisotropy at “macro level” is proposed as a smart structural solution to replace single layer foam headliners of the same weight and thickness. In this paper, a parametric study on the cylinder/matrix configuration is performed and the results are compared with these of single layer expanded polystyrene foam. The structure is subsequently optimized for the best performance in mitigation of rotational acceleration and velocity. Oblique impact results show that the parameters such as the number of cylinders in a given structure, and the compliance of the matrix foam significantly affect the extent of rotational acceleration and velocity mitigation. Optimized composite foam configurations are subsequently proposed and they demonstrate a mitigation of rotational acceleration and velocity up to 44 and 19%, respectively. Moreover, relevant global head injury criteria such as HIC (Head Injury Criterion), RIC (Rotational Injury Criterion), HIPmax (Head Impact Power), GAMBIT (Generalised Acceleration Model for Brain Injury Threshold), and BrIC (Brain Injury Criterion) demonstrated reduction up to 27, 67, 31, 26, and 19%, respectively.@en

Polymeric foams are extensively used in applications such as packaging, sports goods and sandwich structures. Since in-service loading conditions are often multi-axial, characterisation of foams under multi-axial loading is essential. In this article, quasi-static combined shear-compression behaviour of isotropic expanded polystyrene foam and anisotropic polyethersulfone foam was studied. For this, a testing apparatus which can apply combined compression and transverse shear loads was developed. The results revealed that the shear and compression energy absorption, yield stress and stiffness of foams are dependent on deformation angle. The total energy absorption of the anisotropic polyethersulfone foam is shown to be direction dependent in contrast to isotropic expanded polystyrene. Furthermore, for similar relative density, polyethersulfone foam absorbs more energy than expanded polystyrene foam, regardless of deformation angle. This study highlights the importance of correct positioning of foam cells in anisotropic foams with respect to loading direction to maximise energy absorption capability @en

Anisotropy in foams generally originates from cell elongation in a certain direction. In this study, a composite concept is utilized to create anisotropy in foams at macro level. For this, layered composite foam is proposed by combining discrete layers of expanded polystyrene foam foam with different densities. The layers are positioned in parallel with the prime loading direction. The compression and biaxial combined shear-compression behavior of the composite foams are studied and compared with single-layer expanded polystyrene foam of equivalent density. The biaxial shear-compression test results demonstrate that the composite concept enables to decouple shear and compression properties of foam for a given overall density. In compression loading, the composite foam behavior is similar to that of single-layer foam of similar density, while in biaxial loading, the composite foam shows lower shear resistance than single-layer foam. Moreover, in biaxial loading, parameters such as the number of layers and the density difference between the high- and low-density layers affect the extent of decrease in shear resistance, while the compression stress component depends solely on the overall density of the composite foam. One of the potential applications of this behavior could be in protective helmets for mitigation of the head rotational acceleration.@en

Oblique impact is the most common accident situation that occupants in traffic accidents or athletes in professional sports experience. During oblique impact, the human head is subjected to a combination of linear and rotational accelerations. Rotational movement is known to be responsible for traumatic brain injuries. In this article, composite foam with a column/matrix composite configuration is proposed for head protection applications to replace single-layer uniform foam, to better attenuate rotational movement of the head during oblique impacts. The ability of composite foam in the mitigation of rotational head movement is studied by performing finite element (FE) simulations of oblique impact on flat and helmet shape specimens. The performance of composite foam with respect to parameters such as compliance of the matrix foam and the number, size and cross-sectional shape of the foam columns is explored in detail, and subsequently an optimized structure is proposed. The simulation results show that using composite foam instead of single-layer foam, the rotational acceleration and velocity of the headform can be significantly reduced. The parametric study indicates that using a more compliant matrix foam and by increasing the number of columns in the composite foam configuration, the rotation can be further mitigated. This was confirmed by experimental results. The simulation results were also analyzed based on global head injury criteria such as head injury criterion, rotational injury criterion, brain injury criterion and generalized acceleration model for brain injury threshold which further confirmed the superior performance of composite foam versus single-layer homogeneous expanded polystyrene foam. The findings of simulations give invaluable information for design of protective helmets or, for instance, headliners for the automotive industry.@en

Although current standard bicycle helmets protect cyclists against linear acceleration, they still lack sufficient protection against rotational acceleration during oblique impact events. Rotational acceleration is correlated with serious traumatic brain injuries such as acute subdural haematoma and thus should be minimized. This study proposes using highly anisotropic polyethersulfone foam for bicycle helmet liners in order to limit the rotational acceleration. Helmet prototypes, made of polyethersulfone foam with cell anisotropy direction perpendicular to the head, have been produced and compared to a standard commercial helmet. Standard helmets consist of expanded polystyrene foam. Oblique impact tests were performed to measure both linear and rotational accelerations and impact pulse duration. Results demonstrate that the peak rotational acceleration of the polyethersulfone prototype helmet showed a decrease of around 40% compared to the reference expanded polystyrene helmet. Moreover, the peak linear acceleration showed an average decrease of about 37%. Upon impact, the polyethersulfone helmet showed improved head injury protection when analysed based on global biomechanical head injury criteria such as HIC15 and HICrot as well as generalized acceleration model for brain injury threshold, brain injury criterion and head impact power, with a predicted sixfold decrease in likelihood of concussion.@en

Rotational acceleration experienced by the head during oblique impacts is known to cause traumatic brain injuries. It is hypothesized that shear properties of a foam layer, used for head protection (e.g., protective helmet liners, headliners in cars) can be related to the extent of rotational acceleration transmitted to the head. Furthermore, it is hypothesized that by introducing anisotropy in a foam layer, rotational acceleration can be mitigated. In this study, an anisotropic composite foam concept is proposed to mitigate head rotational acceleration, hence reducing the risk of traumatic brain injuries. The composite foam concept introduces anisotropy in a foam at the “macro level”, combining different densities of foam in layered and quasi‐fiber/matrix configurations. The performance of expanded polystyrene (EPS) composite foams in quasi‐static compression and combined shear‐compression loading and also linear and oblique impact experiments, has been compared with the performance of single layer EPS foam of similar thickness and density. The results of oblique head impact have been analyzed by global head injury criteria such as HIC, HICrot, and HIP. The composite foam concept demonstrates a great potential to be utilized in applications such as protective helmets due to the significant mitigation of brain injury risk.@en

Rotational acceleration experienced by the head during oblique impacts is known to cause traumatic brain injuries. It is hypothesized that shear properties of a foam layer, used for head protection (e.g., protective helmet liners, headliners in cars) can be related to the extent of rotational acceleration transmitted to the head. @en

n this study, different configurations of layered composite foam liners for a protective helmet were prepared by arranging layers of EPS foams with different densities in a series configuration. The performance of the layered "composite foams" in terms of peak force/accelerations and time duration in linear impact were compared with single layer homogenous EPS foam. Linear impact tests were performed for two different initial energies of 40 and 66 J. Results demonstrate that in a liner with a density gradient through the thickness, positioning the higher density close to the head can reduce the peak accelerations transferred to the head. In addition, in his paper, the effect of using different materials as a helmet shell on the performance of a helmet in linear impact has been studied. For this purpose high energy absorbing composites such as Curv® and silk/HDPE have been benchmarked against conventional shell materials such as polycarbonate. Results demonstrated the superior performance of silk/HDPE composite compared to the other materials for more localized loads.@en

In this paper, a new anisotropic material concept namely composite foam is proposed as an alternative to next generation helmet liners which can potentially reduce head rotational accelerations. The Layered Composite foam concept comprises of foam layers with different densities which are glued to each other in a parallel or series configuration. Initial experiments such as static combined shear-compression and linear impact tests have been performed. The performance of composite foams has been compared with a commercial expanded polystyrene bead foam (EPS), with nominal density of 80 kg/m3, which is currently the most used material for bicycle helmets. In this study the two types of composite foam with parallel and series configuration have been produced. Combined shear compression results indicate the parallel configuration is more suitable in terms of shear-compressive properties as well as energy absorption. Moreover, linear impact results indicate that the composite foam concept can mitigate peak forces compared to a standard EPS foam.@en

Conventional composites are susceptible to impact loading due to their low toughness. Novel annealed steel fibres possess a unique combination of high stiffness and high strain to failure. A range of composite laminates incorporating various steel fibre architectures with thermoplastic and thermoset matrices were produced and the low-velocity penetration impact resistance was characterized by falling weight impact tests, showing the high potential toughness of steel fibre composites. The effect of different parameters was determined. High matrix strain to failure allows a better exploitation of the steel fibre ductility. The higher absorbed energy up to penetration, in case of laminates with lower levels of fibre/matrix adhesion is attributed to fibre debonding, potential for more plastic deformation, and pull-out mechanisms. Thinner fibres are more sensitive to premature failure due to inclusions in the steel fibres. Cross-ply laminates show higher energy absorption, probably due to increased delamination, whereas woven fibre structures lead to more localized damage. A preliminary study shows that layer by layer (‘macro’) hybridization of carbon and steel fabrics leads to penetration impact resistance close to the pure steel fibre composite, in case the steel plies are placed on the outside surfaces, showing a significant positive effect of hybridization.@en

Shape memory polymer composites based on a blend of thermoplastic polyurethane (TPU) segmented block copolymer and poly(ε-caprolactone) (PCL) with weight ratio of 70/30 and various nanomagnetite contents (0–5 wt%) were prepared by melt blending of TPU and PCL, together with a masterbatch of TPU/nanomagnetite. The samples were compounded for 10 min at 200 °C using an internal mixer. Synthesized nanomagnetite powder was introduced to the masterbatch via a solution mixing method using a high-intensity ultrasonic horn. Subsequently, thermal, mechanical, rheological and electrical properties of the TPU/PCL/nanomagnetite shape memory composites were investigated through various tests. The degree of crystallization of the PCL component in the composite structure was inspected by differential scanning calorimetry (DSC) and X-ray diffraction measurements. The results revealed that the percentage of crystallinity and the melting temperature of the PCL component changed in the presence of magnetite nanoparticles, which was related to the nanoparticles acting as nucleants. Observing a single glass transition temperature (T g) in DSC thermograms of the samples was indicative of good compatibility of the TPU and PCL components in the composite structure. This was also confirmed by dynamic-mechanical analysis in which the loss modulus curves showed a single glass transition temperature. Moreover, the loss modulus peak at glass transition was lowered and broadened by addition of nanomagnetite, by which it was assumed that introducing nanoparticles into the system changed the mechanism of glass transition due to particle–matrix interactions. The dynamic rheological and electrical resistivity experiments verified the existence of a low percolation threshold at about 2 wt% nanomagnetite. The state of nanomagnetite dispersion in the masterbatch and the microstructure of the ternary composites were characterized by scanning electron microscopy. Finally, adding nanomagnetite led to weakening of shape recovery of the polymer blend, with shape recovery dropping to 70 % at 5 % of nanomagnetite.@en

Polymer foams are extensively used in lightweight structures, often as energy absorbers. Since most of the loading modes in real life are complex, characterization of core materials under multi-axial loading is of great importance. In this work, a new testing apparatus for measuring combined shear-compression loading of sandwich core materials has been developed. The behavior of expanded polystyrene (EPS) foams has been studied in quasi-static mode. Three different densities of EPS foam have been tested under different angles of displacement (the resultant of shear and compression displacement), particularly 0° 15°, 45°, and 60°.The results reveal that the parameters such as energy absorption in (shear and compression) up to densification, yield stress and elastic modulus of the EPS foam have a strong dependency on the angle of displacement as well as the density of the foams.@en

yclists during bicycle traffic accidents, are prone to oblique impact which leads to rotational accelerations. Rotational acceleration is known to cause significant brain injuries, and should be minimized. Foam materials inside bicycle helmets undergo a combination of shear and compression loads during oblique impact. Therefore, developing an apparatus and a test method which can apply a combination of shear and compression loads to the foam at the same time is of great importance. This testing method has a broad application which is not only limited to the foams for bicycle helmet applications but has general relevance to sandwich core materials in structural composites. In this paper, the shear-compression behavior of different types of foams under different angles, particularly 15 ͦ, 45 ͦ and 60 ͦ is investigated and compared to the standard EPS foam used in bicycle helmets. Shear stresses in anisotropic PES foams under different angles in the combined shear-compression test were lower than for standard EPS, which is favourable because they lead to high rotational acceleration. The peak rotational and translational accelerations of the PES prototype helmets were measured by a rotational impact test set-up and showed a dramatic decrease of around 40% compared to the reference EPS helmet, however at increased pulse duration.@en

lthough current standard bicycle helmets provide protection against so-called linear acceleration, they cannot deliver sufficient protection against rotational acceleration during oblique impact events. These events can cause severe head injuries and the rotational accelerations need to be minimized. We pursue this goal by developing anisotropic foams for bicycle helmets and define test methods to characterize foams under oblique loading. (1) (PDF) DEVELOPMENT OF ANISOTROPIC FOAMS AND CHARACTERIZATION METHODS FOR BICYCLE HELMETS. Available from: https://www.researchgate.net/publication/320110420_DEVELOPMENT_OF_ANISOTROPIC_FOAMS_AND_CHARACTERIZATION_METHODS_FOR_BICYCLE_HELMETS [accessed Apr 28 2020].@en

This study investigates the impact-energy absorbing potential of steel fibre reinforced composites with different matrices. The composites were subjected to low-velocity impact using the drop-weight impact test. The interfacial adhesion strength between matrices and steel fiber was characterized by a transverse three point bending test. It was found that factors such as fibre architecture, matrix strain to failure, and the level of adhesion can play a crucial role in the absorbed energy for penetration. A cross-ply non-crimp fabric showed higher energy absorption than a plain woven fabric. Absorbed energy increased with polymer matrix strain to failure and lower fibre-matrix adhesion. (1) (PDF) On the potential of fine steel fibres to create stiff but tough polymer composites. Available from: https://www.researchgate.net/publication/293222932_On_the_potential_of_fine_steel_fibres_to_create_stiff_but_tough_polymer_composites [accessed Apr 28 2020].@en

Recent studies on inorganic/polymer nanocomposites have shown enhancements in thermal, mechanical, and chemical properties over the neat polymer without compromising density, toughness, and processibility. When nanoparticles are incorporated into the polymer matrix, significant enhancements in thermal and mechanical properties of the nanocomposite are observed. The present study is focused on the preparation and characterization of nanosize magnetite-reinforced PU composites, which induces magnetic properties to a specific thermoplastic polyurethane elastomer. The nanocomposites are prepared and the effects of magnetite content on thermal, mechanical, and magnetic properties of the nanocomposites are evaluated. Ultrasonication was used to disperse the nanoparticles and break up any large clumps and aggregates and followed by mechanical mixing. The magnetic nanocomposites were characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). Characterization of the magnetic nanocomposite by FT-IR showed a successful incorporation of magnetite nanoparticles into the polymeric matrix. TGA and magnetometry of the magnetic nanocomposites revealed the amount of magnetite that was incorporated into the polymeric phase. Finally, the corresponding magnetization behavior of the nanocomposites was studied.@en