Investigation of fiber/matrix adhesion: test speed and specimen shape effects in the cylinder test

The cylinder test, developed from the microdroplet test, was adapted to assess the interfacial adhesion strength between fiber and matrix. The sensitivity of cylinder test to pull-out speed and specimen geometry was measured. It was established that the effect of test speed can be described as a superposition of two opposite, simultaneous effects which have been modeled mathematically by fitting two parameter Weibull curves on the measured datas. Effects of the cylinder size and its geometrical relation on the measured strength values have been analyzed by finite element method. It was concluded that the geometry has a direct influence on the stress formation. Based on the results achieved, recommendations were given on how to perform the novel single fiber cylinder test

TECNICA ESTRATTIVA E STORIA NELLA CAVA MADRE DI CANDOGLIA

La nota presenta una sintesi storico tecnica delle coltivazioni di marmo rosa destinato alla costruzione e manutenzione del Duomo di Milano. Le cave a ciò destinate si trovano all’imbocco della Val d’Ossola e, in particolare negli ultimi 40 anni, hanno visto lo sviluppo della principale di esse, la Cava Madre, una caverna sotterranea di ragguardevoli dimensioni. L’aspetto storico della coltivazione riguarda le modalità con cui venne riservato a tale contesto estrattivo la prerogativa di fornitore della Veneranda Fabbrica del Duomo, nonché le tecniche estrattive, di trasporto e di lavorazione per strutture e fregi del duomo. Negli ultimi 15 anni, l’estrazione si è concentrata sull’imbocco della caverna, sviluppando la tecnica del taglio con filo e con tagliatrice a nastro, dopo aver realizzato un’approfondita modellazione numerica degli scavi, una caratterizzazione geomeccanica dei materiali ed aver approntato un articolato sistema di monitoraggio geotecnico, tuttora attivo ed aggiornato, tale da poter seguire lo sviluppo tenso deformativo della caverna

Interfacial shear strength of Polylactic Acid-Kenaf fibre biocomposites

This paper reported the interfacial shear strength (IFSS) between kenaf fibre (KF) and polylactic acid (PLA) matrix which was measured using microbond tests device. The value of IFSS obtained in PLA-KF is comparable to other polymer with natural fibre reinforcements. The properties of single kenaf fibre was determined from tensile tests and also described in this paper. From single kenaf fibre properties, various mechanical properties can be estimated for various applications

Critical measurement issues in the use of wire potentiometers for the structural health monitoring of slender structures: the case of the Duomo di Milano main spire

During the restoration of the Duomo di Milano main spire, a monitoring system has been set up in order to have an early detection of potential risks of the spire. A scaffolding for the restoration activities was mounted around the spire, and it had a section exposed to the wind actions much wider than the spire itself. Any possible contact between the spire and the scaffolding had to be prevented, even under the strongest winds expected in Milan, since the stability of the extremely slender marble spire could be compromised in case of contact. A safety gap between the two substructures was granted during the construction phase; however, the deflection of the spire could not be reliably predicted by numerical models. Therefore, it was decided to continuously monitor the actual gap value, together with other measurements, helping in a thorough understanding of the spire and scaffolding movements. The gap monitoring was measured by three-wire potentiometers, mounted to measure the relative position between the scaffolding and the spire in the section where the gap was the narrowest: the top balcony. This measurement was considered one of the most critical for the safety of the spire; therefore, every choice has been aimed at redundancy and safety. Moreover, any systematic effect has to be compensated for. A main issue related to the use of wire potentiometers is that these sensors estimate the amplitude of the displacement but does not provide any information on its direction. Since the horizontal displacement of slender structures can be in any direction, according to the wind and sun radiation conditions, the output of a wire potentiometer is also affected by displacements in the direction normal to its sensitivity axis, leading to a systematic effect in the measurements (cross-talk effect). This aspect hardly finds literature attention, but it can play a major role if the safety of the structure is monitored with wire potentiometers. This paper focuses on the estimation and compensation of this cross-talk effect, to provide reliable measurements in the monitoring of slender structures. Numerical and experimental validation of the proposed approach demonstrates the need to compensate for the cross-talk effects for a proper uncertainty estimation and then the validity of the proposed method

Una grande caverna per l'estrazione di pietra ornamentale: il caso della Cava Madre del Duomo di Milano a Candoglia (VCO)

The geological, geo-mechanical and numerical studies carried out for the static design of the underground exploitation cavern of the Cava Madre of Candoglia (VCO, Italy) are presented and discussed in the paper. This underground cavern was constructed for the mining exploitation of a large sub-vertical vein of pink marble that was necessary for the construction of Milan Cathedral. This marble orebody was gifted to the Milan Cardinal by the Duke Gian Galeazzo Visconti in the 1387 and the exploitation is today active (only in the underground cavern and no more in open pits) since it is necessary to provide the marble (slabs, blocks for the statues, etc.) for the cathedral maintenance. The cavern started from the mountain side and entered sub-horizontally inside the mountain for a length of about 50m. Now the cavern has a width of more than 20m and a variable height that, in the portal area, is of about 40m. Due to a stability problem of the cavern wall that occurred more than ten years ago in the deepest portion of the cavern, it was decided to restart the exploitation works in the portal area where detailed "geo" investigations have discovered a large portion of very good marble. To permit a safe extraction of this new portion of the orebody it was necessary to develop both side investigations and numerical computations. Three dimensional and two dimensional FLAC models were developed to understand the static conditions of the cavern in the present situation and after the development of the forecasted exploitation. Thanks to a very good monitoring of the cavern during the years it was also possible to carry out a detailed back analysis that permitted to validate the quality of the numerical results. Before carrying out the new mining works it was necessary to demolish several reinforced concreted beams that were built up in the seventies and that were not able to fulfil the displacements induced by the new excavations as shown by the numerical model results. The design of the new beams with a larger cross section than the previous ones is discussed in the paper together with the numerical model results after the development of the new excavation

Una grande caverna per l'estrazione di pietra ornamentale: il caso della Cava Madre del Duomo di Milano a Candoglia (VCO)

The geological, geo-mechanical and numerical studies carried out for the static design of the underground exploitation cavern of the Cava Madre of Candoglia (VCO, Italy) are presented and discussed in the paper. This underground cavern was constructed for the mining exploitation of a large sub-vertical vein of pink marble that was necessary for the construction of Milan Cathedral. This marble orebody was gifted to the Milan Cardinal by the Duke Gian Galeazzo Visconti in the 1387 and the exploitation is today active (only in the underground cavern and no more in open pits) since it is necessary to provide the marble (slabs, blocks for the statues, etc.) for the cathedral maintenance. The cavern started from the mountain side and entered sub-horizontally inside the mountain for a length of about 50m. Now the cavern has a width of more than 20m and a variable height that, in the portal area, is of about 40m. Due to a stability problem of the cavern wall that occurred more than ten years ago in the deepest portion of the cavern, it was decided to restart the exploitation works in the portal area where detailed “geo” investigations have discovered a large portion of very good marble. To permit a safe extraction of this new portion of the orebody it was necessary to develop both side investigations and numerical computations. Three dimensional and two dimensional FLAC models were developed to understand the static conditions of the cavern in the present situation and after the development of the forecasted exploitation. Thanks to a very good monitoring of the cavern during the years it was also possible to carry out a detailed back analysis that permitted to validate the quality of the numerical results. Before carrying out the new mining works it was necessary to demolish several reinforced concreted beams that were built up in the seventies and that were not able to fulfil the displacements induced by the new excavations as shown by the numerical model results. The design of the new beams with a larger cross section than the previous ones is discussed in the paper together with the numerical model results after the development of the new excavations