The present work aims at understanding the stochastic matrix crack evolution in CFRP cross-ply laminates under tension–tension fatigue loading. An experimental campaign was carried out on twenty-three specimens at different stress levels, while two optical techniques were used for the in-situ monitoring of the accumulation of transverse matrix cracks. The results showed a significant scatter in crack evolution among specimens. This stochastic behaviour was further investigated using image analysis and numerical modelling. It was found that transverse matrix cracks can be classified into the independent and dependent cracks based on a critical crack spacing. Furthermore, the severity of interaction among cracks was quantified by introducing a dependent crack ratio. Finally, a strength-based probabilistic model was proposed to describe the scattering regime of the crack evolution. The agreement between model and test results indicates that local strength variations of 90 plies are the dominant scattering source governing the initial fatigue resistance to cracking and determining the accumulation of transverse matrix cracks among specimens. These results may provide a new insight into the stochastic nature of matrix cracking in composite laminates and aid in the design of fatigue resistance properties.

This paper presents the results of an experimental campaign carried out to characterise the mechanical properties of multi-wythe masonry infrastructure in the city of Amsterdam. Samples were extracted from a 1.2 m thick bridge’s pillar constructed in 1882. For the characterisation of shear and compressive properties of masonry, tests on cores with a 100 mm diameter were performed at the Stevinlaboratorium of Delft University of Technology. Samples were extracted along different locations in the wall thickness to evaluate the effect of exposure to environment conditions. Overall, the study provides a first insight on the mechanical properties of multi-wythe masonry city infrastructure and knowledge regarding the sampling and testing strategy for these structures. In turn, this will increase the knowledge on multi-wythe masonry, which is limited in literature, and will support the assessment of many infrastructures in typical Dutch canal cities.

Ice impact is quite common and may become critical especially if it involves the transportation sector. Simulation tools may help in the structural design phase to increase the ability to withstand this kind of impact and/or to analyse the effect under extreme weather conditions. Such tools require an accurate description of the mechanical behaviour and therefore a detailed investigation about the dynamic mechanical properties of ice is of great interest. In the present work, material characterizations of ice, including tensile and compressive tests, were carried out under different strain rates. Two different material models (i.e., the modified Johnson-Cook model and Johnson-Holmquist II model) were calibrated. Then, impact tests using ice as a projectile with aluminium panels as a target were conducted to validate the material models of ice under impact loading. Furthermore, the replication effect of ice projectiles was investigated under different impact energies based on the mechanical responses and damage phenomena of ice for both models. Results showed that while both models are able to provide reliable predictions of the impact behaviour of ice projectiles, the Johnson-Holmquist II model presents a better performance as impact energy increases.

Foamed concrete is an essential material in engineering that can be categorized into two types based on density distribution, namely uniform foamed concrete (UFC) and gradient foamed concrete (GFC). However, there exists a research gap concerning the mesoscopic deformation mechanism of UFC and GFC. The objective of this research is to bridge this gap by examining the quasi-static compression characteristics of UFCs with three distinct densities and GFCs with different density sequences. The results reveal that the strength of pore walls significantly influences the failure mechanism of UFCs with varying densities. Specifically, UFCs with low density exhibit weak pore-wall strength, leading to stress concentration at the pore-wall junction. During compression, these weak pore walls are widely dispersed within the specimen, resulting in a powdering failure mode. Conversely, UFCs with high density possess stronger pore walls, which prevent the powdering failure mode by maintaining adequate pore-wall strength. Nevertheless, the existence of a dominant crack within the specimen results in a splitting failure mode. In the context of GFCs, deformation occurs in a sequence from low to high density, with each layer exhibiting a failure mode corresponding to its density. Note that the last-deforming layer in this brittle gradient foam cannot attain the strength of the corresponding uniform foam. This is due to the failure of the second layer, which results in uneven contact surfaces and prompts the third layer to crack simultaneously. Finally, a statistical model is developed to forecast the compressive Stress–strain curve of foamed concrete, demonstrating remarkable agreement with experimental data.

The present work aims at providing insights on the material characterization of multi-wythe masonry infrastructure, in particular exploring a through-thickness effect of mechanical properties and benchmarking the core testing as an efficient slightly-destructive testing method. An experimental campaign was carried out to characterize shear, compressive and bond properties of a 1.2-m thick bridge's pillar constructed in 1882 in the city of Amsterdam (the Netherlands). Both cores and rectangular samples (e.g. prisms, triplets, couplets) were extracted across different locations in the wall thickness to evaluate the effect of exposure to environment conditions and to verify the capability of core testing methods. Results show that the masonry close to the water side (external) showed higher values of elastic modulus and lower values of flexural bond properties with respect to masonry inside the pillar. As for the capability of core testing on multi-wythe masonry, generally cores would present similar compressive/shear properties compared with rectangular samples. Besides, bond patterns and dimensions of cores showed negligible effect on compressive properties; However, this needs to be extensively verified by considering other masonry typologies. Overall, the study provides a first insight on the mechanical properties of multi-wythe masonry urban infrastructure and knowledge regarding the sampling and testing strategy for these structures. In turn, this will increase the knowledge on multi-wythe masonry, which is limited in literature, and will support the assessment of many infrastructure in typical Dutch canal cities by providing input for calculation methods.

Rain erosion may cause substantial damage to aircrafts during supersonic flight. Such event is investigated here via high-speed waterjet impact on composite laminates. An experimental setup is developed to produce waterjets with the speed up to 700m/s and a finite element model of the waterjet-composite impact event is established. The consistency of experiment and simulation results validates the adopted numerical methods. The distribution of the water-hammer pressure is non-uniform and the maximum pressure occurs near the contact periphery when the water is about to eject laterally. After a high-speed (300∼560m/s) waterjet impacts a composite laminate, the impacted surface depression is observed, and the typical surface damage presents a central region with no visible surface damage surrounded by a faded “failure ring” with resin removal, matrix cracking and minor fiber fracture. Delamination occurs at the interfaces of adjacent layers with unequal dimensions and longitudinal matrix cracking appears on the back surface. Both the velocity and the diameter of waterjets are crucial factors on CFRP damage extents. Water-hammer pressure, the stagnation pressure and propagation of stress waves are failure mechanisms for most matrix damage in CFRP impacted by waterjets.

Ply-block size and stress level effect on accumulation of transverse cracks and delamination are investigated during early fatigue life of CFRP laminates. Tension-tension fatigue tests under different stress levels were performed for two cross-ply configurations. Edge observation with digital cameras, digital image correlation and acoustic emission were employed for in-situ damage monitoring. Transverse cracks were dominant for [0/90₂]_s laminates with almost non-existent delamination, while different interactive levels between both damage mechanisms occurred for [0₂/90₄]_s laminates. Poisson's ratio identifies whether early fatigue damage is dominant by transverse cracks or involves delamination. Cumulative AE energy is a helpful indicator of crack density.

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 monitored the damage evolution. It was found that different accumulation process and interactive levels between transverse matrix cracks and delamination exist for specimens with similar stiffness degradation. A linear increase of stiffness degradation was observed with the increase of matrix crack density, while the growing trend of stiffness degradation converged with the increase of delamination.

Carbon fiber-reinforced composite materials are widely employed in aircraft structures due to their high specific strength and high specific modulus. However, the poor impact resistance of carbon fiber reinforced composites creates challenges for aircraft design and maintenance. The introduction of a layer of glass fibers in the hybrid composites can effectively improve the impact performance of the composite laminate. In this work, finite element models for low-velocity impact of carbon fiber laminate and glass fiber laminate are established and validated. A VUMAT subroutine in Abaqus is implemented to evaluate the progressive damage of the composite materials, and a cohesive-zone model is employed to simulate the interface failure behavior. The impact resistance of hybrid composite laminates is systematically studied based on the results of the finite element simulation. Ten different hybrid configurations are studied and compared with a composite laminate having a single type of fiber reinforcement. The numerical results for the global mechanical response, damage modes and characteristics are extracted and systematically discussed. The results suggest that laminates having carbon fiber layers on the top and bottom surfaces with glass fiber layers between them perform the best in terms of energy absorption. When the glass fiber layers are used for the top and bottom surfaces with carbon fiber layers as the core, the presence of a carbon fiber layer with a ±45 ° orientation can help to reduce the damage area.

The mechanical characterization of textile composites is a challenging task, due to their nonuniform deformation and complicated failure phenomena. This article introduces a three-dimensional mesoscale finite element model to investigate the progressive damage behavior of a notched single-layer triaxially-braided composite subjected to axial tension. The damage initiation and propagation in fiber bundles are simulated using three-dimensional failure criteria and damage evolution law. A traction-separation law has been applied to predict the interfacial damage of fiber bundles. The proposed model is correlated and validated by the experimentally measured full field strain distributions and effective strength of the notched specimen. The progressive damage behavior of the fiber bundles is studied by examining the damage and stress contours at different loading stages. Parametric numerical studies are conducted to explore the role of modeling parameters and geometric characteristics on the internal damage behavior and global measured properties of the notched specimen. Moreover, the correlations of damage behavior, global stress-strain response, and the efficiency of the notched specimen are discussed in detail. The results of this paper deliver a throughout understanding of the damage behavior of braided composites and can help the specimen design of textile composites.