Size-effect independence of hybrid fiber-reinforced roller-compacted concrete fracture toughness

The present paper aims to prove the size-effect independence of Hybrid Fiber-Reinforced RCC (HyFR-RCC) fracture toughness determined through the Modified Two-Parameter Model (MTPM). A micromechanical numerical model is applied to simulate the fracture behavior of seven series of single edge-notched specimens, made of both plain-RCCs and FR-RCCs (single and hybrid reinforcements), subjected to three-point bending. The MTPM is applied to the numerical load vs CMOD curves to compute the fracture toughness. A comparison with experimental values, available in the literature, is performed. Therefore, RCC specimens with different sizes are numerically simulated and the fracture toughness is analytically determined through the MTPM, proving the size-effect independence

A novel methodology for fatigue assessment of Ductile Cast Iron (DCI) with solidification defects

In the present research work, the fatigue strength assessment of a DCI containing solidification defects is theoretically carried out by means of a procedure implementing: (i) a defect content analysis, (ii) the varea-parameter model, and (iii) the multiaxial critical plane-based criterion by Carpinteri at al. An experimental campaign available in the literature, performed on DCI specimens under multiaxial fatigue loading, is analysed. The comparison between the obtained results and the experimental data shows a quite satisfactory agreement, highlighting the criterion accuracy

Experimental and numerical study on the fatigue behaviour of the shot-earth 772

The present research work is devoted to the mechanical, fracture and fatigue experimental characterization of the shot-earth 772, with a particular attention to its fatigue behaviour. To such an aim, an extensive experimental program has been carried out, consisting of: (i) flexural and compression tests, (ii) three-point bending fracture tests, and (iii) bending and compression cyclic tests. Moreover, a FE numerical model is employed to simulate both the above bending and compression cyclic tests, after the input data validation performed by simulating the above fracture tests. The numerical fatigue lifetimes are compared with the corresponding experimental ones for both pulsating bending and compression, highlighting the model accuracy. Finally, the contours of both the damage parameter and the reduced Young modulus are plotted showing the evolution of fatigue damage

Crack path estimation in the shot-earth 772 by a discrete element method

In the present paper, the fracture behaviour of the shot-earth 772, in terms of crack path, is numerically investigated. To such an aim, a version of the lattice discrete element method is used to numerically simulate fracture toughness testing performed, on the shot-earth 772, by employing the Modified Two-Parameter model. A comparison between the numerical crack path and the experimental ones is performed, highlighting as the lattice discrete element method is able to capture the kinked crack shape, typical of quasi-brittle material

Flexural and fracture behaviour of a cement-based material reinforced with GO nanoplates

In the present research work, the mechanical properties of a cement-based material reinforced with Graphene Oxide (GO) nanoplates are experimentally investigated. In particular, a detail experimental campaign, consisting of three-point bending tests on both unnotched and edge-notched specimens, is performed in order to determine flexural strength and fracture toughness. More precisely, the flexural strength is computed as a function of the experimental values of the peak load according to UNI EN Recommendation, whereas the fracture toughness is analytically determined according to the Modified Two-Parameter Mode

Lifetime estimation for 316 stainless steel specimens by using a critical plane approach

The lifetimes of 316 stainless steel specimens are herein evaluated using the multiaxial critical plane-based criterion by Carpinteri et al. for high-cycle fatigue (HCF) loading with constant amplitude. In the present paper, the stress-based version of such a criterion is applied to assess the results of experimental tests under HCF triaxial loading, the hollow cylindrical dog-bone specimens being subjected to a quenching heat treatment. The analytical results of fatigue life and initial crack plane orientation are compared with the experimental data

In Vivo Imaging of Transiently Transgenized Mice with a Bovine Interleukin 8 (CXCL8) Promoter/Luciferase Reporter Construct

One of the most remarkable properties of interleukin 8 (CXCL8/IL-8), a chemokine with known additional functions also in angiogenesis and tissue remodeling, is the variation of its expression levels. In healthy tissues, IL-8 is barely detectable, but it is rapidly induced by several folds in response to proinflammatory cytokines, bacterial or viral products, and cellular stress. Although mouse cells do not bear a clear homologous IL-8 gene, the murine transcriptional apparatus may well be capable of activating or repressing a heterologous IL-8 gene promoter driving a reporter gene. In order to induce a transient transgenic expression, mice were systemically injected with a bovine IL-8 promoter–luciferase construct. Subsequently mice were monitored for luciferase expression in the lung by in vivo bioluminescent image analysis over an extended period of time (up to 60 days). We demonstrate that the bovine IL-8 promoter–luciferase construct is transiently and robustly activated 3–5 hours after LPS and TNF-α instillation into the lung, peaking at 35 days after construct delivery. Bovine IL-8 promoter–luciferase activation correlates with white blood cell and neutrophil infiltration into the lung. This study demonstrates that a small experimental rodent model can be utilized for non-invasively monitoring, through a reporter gene system, the activation of an IL-8 promoter region derived from a larger size animal (bovine). This proof of principle study has the potential to be utilized also for studying primate IL-8 promoter regions

Fatigue lifetime assessment of AM metallic components according to a strain-based criterion

Over the last few years, the fatigue behaviour of Additive Manufacturing (AM) metallic components has been extensively investigated from an experimental point of view, whereas only few theoretical works are available in the literature. In such a context, the fatigue behaviour of AM metallic specimens under cyclic loading is theoretically investigated herein. More precisely, fatigue tests available in the literature are simulated by means of a strain-based fatigue criterion proposed by Carpinteri and co-workers. In order to assess the validity of the present criterion, theoretical results are compared with both experimental ones and those derived through the Fatemi-Socie fatigue criterion

Influence of hot-spot on crack path and lifetime estimation of fretting-affected steel components

The crack nucleation orientation of fretting-affected components made of AISI1034 steel and 35NCD16 steel is analysed in the present paper. In particular, both cylinder-to-flat and sphere-to-flat contact configurations in partial slip regime are simulated by means of an analytical methodology based on elastic assumptions. Different crack nucleation locations on the contact surface are considered in order to estimate both the crack nucleation orientation and the lifetime. Satisfactory results are obtained by employing such a methodology, especially when both the stress state within the specimen and the relative slip between the specimen and the pad are taken into account in the fretting assessment procedure