A study on fiber-arrangement close to the root of a sharp notch, for short fiber-reinforced thermoplastics

An approach, which aims at the morphological characterization near the sharp notch of specimens, has been developed for Short Fiber-Reinforced Thermoplastics. This work is directly related to the fa- tigue behavior of such materials, since the early stages of the cyclic damage are strictly influenced by the local microstructure at the stress concentration sites. Therefore, a comprehensive description of fi- bers\u2019 arrangement is needed in order to proceed with a modeling activity for the lifetime duration esti- mation. To this end, a semi-automatic tool has been developed, which is capable of evaluating fiber- arrangements through statistical descriptors, after submitting 2D pictures of the notch-tip area. Particu- larly, the attention was focused onto the nearest neighbor distance distribution function and onto a new formulation, which gives information about the level of the fiber-clustering phenomenon. On this basis, the repeatability of results has been evaluated with the goal of stating whether such information can be inherited by lifetime estimating models

fatigue damage and stiffness evolution in composite laminates a damage based framework

Abstract A damage-based design procedure has been developed by the authors to predict the damage evolution and the stiffness degradation in polymeric composite laminates under fatigue loading. For a safe and reliable design against fatigue degradation and failure, the initiation of the main damage mechanisms (off-axis cracks, delamination and fiber failure) as well as their evolution are considered and suitable models are proposed for the quantitative assessment of the lifetime associated to each mechanism. In parallel, the stiffness degradation deriving from the damage evolution over the fatigue life is properly described. After the illustration of the overall damage-based strategy, the paper discusses in details the analysis and modelling of the off-axis crack initiation and propagation. The initiation of cracks in the off axis plies has been proved to be the consequence of a damage process occurring at the microscopic scale since the early stages of fatigue. On this basis, crack initiation prediction is based on the use of local stress parameters: Local Hydrostatic Stress, LHS, and Local Maximum Principal Stress, LMPS, depending on the local degree of multiaxiality of the stress state and accounting for the statistical distribution of the local laminate strength. The propagation phase is then quantified by using a conventional fracture mechanics approach. The model has been implemented in a Matlab procedure for the quantitative evaluation of the crack density in each ply of a laminate during its entire fatigue life. The knowledge of the crack density trend allows the description of the laminate stiffness evolution taking advantage of another model recently developed by the authors, valid for a generic laminate configuration and accounting for the interaction between cracks in the neighbouring plies

Plastic Yielding Around Nanovoids

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Assessment of Debonding-Induced Toughening in Nanocomposites

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Functional characterization of peach GOLVEN-like peptides in model systems

Peach (Prunus persica L. Batsch) produces climacteric fleshy fruits; their ripening is strictly regulated and relies mainly on the action of two hormones, auxin and ethylene. A peptide belonging to GOLVEN family, CTG134, was identified some years ago as a possible candidate to regulate the interaction between the two hormones. CTG134 was previously characterized in model systems Arabidopsis thaliana and Nicotiana tabacum, where it demonstrated to influence regulative processes in which above-mentioned hormones are involved. The goal of my PhD project was to test the function of GOLVEN peptides in the regulation of peach fruit ripening. During this thesis work, genes belonging to GOLVEN family were identified, through the use of bioinformatic tools. Among them, genes transcribed during ripening stages, crucial for fruit development, were determined. Another peptide shared the CTG134 expression profile, CTG512. Both were transcribed during climacteric stage and were induced by auxin and not by ethylene. To complete its functional characterization, CTG134 was expressed in Solanum lycopersicum under the control of a fruit specific promoter. Despite no evident phenotype was detected, fruit sampling allowed to test the expression system used by reporter gene GUS, and transcriptomic analysis allowed to verify that CTG134 influences transcription of ethylene related genes possibly inducing its synthesis by inducing expression on an involved gene and increasing tissue sensitivity by partial inhibition of a receptor transcription. To perform preliminary functional characterization, CTG512 was expressed in Arabidopsis e tobacco. Siliques presented ovule and embryo abortion, correlated to transgene expression level. This phenotype is associated to auxin and ethylene action, which are necessary for ovule and embryo development. Results obtained uphold the hypothesis that GOLVEN peptides act as hormone peptides, and together with auxin and ethylene, they participate to regulate fruit developmental steps fundamental for its quality

Energy absorption capability of nanomodified glass/epoxy laminates

Abstract The impact response of standard and clay-modified vacuum-infused glass/epoxy laminates was investigated. The activity was oriented to evaluate the enhancements in the energy absorption capability of the laminates due to the nanomodification. Nanomodification was achieved by using Cloisite 30B nanoclays by Southern Clay. Low velocity impact tests were carried out on flat samples of about 4 mm thicknessby a drop-weight tower. The results clearly indicate that the nanomodified laminates have a greater capability to absorb the impact energy (with up to 30% increases in dissipated energy) with respect to the standard laminates, also in combination with a decrease of the peak impact force (from 10 to 15%). In some ways, this behaviour can be partly justified by the larger damage exhibited by nanomodified laminates, with projected damage areas more than double the damage areas of standard panels, for the same impact energy

Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy

The final slip of about 450 m at about 30 m/s of the 1963 Vaiont landslide (Italy) was preceded by >3 year long creeping phase which was localized in centimeter-thick clay-rich layers (60–70% smectites, 20–30% calcite and quartz). Here we investigate the frictional properties of the clay-rich layers under similar deformation conditions as during the landslide: 1–5 MPa normal stress, 2 × 10^(−7) to 1.31 m/s slip rate and displacements up to 34 m. Experiments were performed at room humidity and wet conditions with biaxial, torsion and rotary shear apparatus. The clay-rich gouge was velocity-independent to velocity-weakening in both room humidity and wet conditions. In room humidity experiments, the coefficient of friction decreased from 0.47 at v 0.70 m/s: full lubrication results from the formation of a continuous water film in the gouge. The Vaiont landslide occurred under wet to saturated conditions. The unstable behavior of the landslide is explained by the velocity-weakening behavior of the Vaiont clay-rich gouges. The formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero, even without invoking the activation of thermal pressurization. This explains the extraordinary high velocity achieved by the slide during the final collapse

The Peach RGF/GLV Signaling Peptide pCTG134 Is Involved in a Regulatory Circuit That Sustains Auxin and Ethylene Actions

In vascular plants the cell-to-cell interactions coordinating morphogenetic and physiological processes are mediated, among others, by the action of hormones, among which also short mobile peptides were recognized to have roles as signals. Such peptide hormones (PHs) are involved in defense responses, shoot and root growth, meristem homeostasis, organ abscission, nutrient signaling, hormone crosstalk and other developmental processes and act as both short and long distant ligands. In this work, the function of CTG134, a peach gene encoding a ROOT GROWTH FACTOR/GOLVEN-like PH expressed in mesocarp at the onset of ripening, was investigated for its role in mediating an auxin-ethylene crosstalk. In peach fruit, where an auxin-ethylene crosstalk mechanism is necessary to support climacteric ethylene synthesis, CTG134 expression peaked before that of ACS1 and was induced by auxin and 1-methylcyclopropene (1-MCP) treatments, whereas it was minimally affected by ethylene. In addition, the promoter of CTG134 fused with the GUS reporter highlighted activity in plant parts in which the auxin-ethylene interplay is known to occur. Arabidopsis and tobacco plants overexpressing CTG134 showed abnormal root hair growth, similar to wild-type plants treated with a synthetic form of the sulfated peptide. Moreover, in tobacco, lateral root emergence and capsule size were also affected. In Arabidopsis overexpressing lines, molecular surveys demonstrated an impaired hormonal crosstalk, resulting in a re-modulated expression of a set of genes involved in both ethylene and auxin synthesis, transport and perception. These data support the role of pCTG134 as a mediator in an auxin-ethylene regulatory circuit and open the possibility to exploit this class of ligands for the rational design of new and environmental friendly agrochemicals able to cope with a rapidly changing environment