Residual strain monitoring during composite manufacturing

This work explores a new possibility in accurate measurement of multi-axial residual strains during the production of composite structures. It investigates the usability of the polarization dependent loss (PDL) of an optical fibre Bragg grating as a sensitive indicator of multi-axial residual strains. The experimental work presented is done on a cross-ply carbon fibre reinforced polymer fabricated using an autoclave cycle

Progress in strain monitoring of tapestries

This paper reports interdisciplinary research between conservators and engineers designed to enhance the long-term conservation of tapestries (tapestry-weave hangings) on longterm display. The aim is to monitor, measure and document the strain experienced by different areas of a tapestry while it is hanging on display. Initial research has established that damage can be identified in the early stages of its inception, i.e., before it is visible to the naked eye. The paper also reports initial results of strain data visualisation that allows curators and conservators to examine how strain develops, thereby facilitating predictions about the changes in the form or condition of the tapestry. Strain data visualisation also allows the strain process to be recorded, thereby facilitating the effective documentation of display methods and conservation interventions. The paper reports the use of point measurements (using silica optical fibre sensors) and full-field monitoring (using 3-D photogrammetry with digital image correlation (DIC))

Long term condition monitoring of tapestries using image correlation

Digital Image Correlation (DIC) is used to extract non-contact full-field three-dimensional displacement and in-plane strains from an historic tapestries. A DIC-based approach is devised that allows the effect of RH variations on a tapestry to be quantified. A historical tapestry has been monitored in a closely controlled environment and in the natural environment. The results revealed that very small variations in RH can have significant effects on strain. An automated long term monitoring approach has been devised to allow strain data to be extracted in real time from tapestries in remote locations. The results show that DIC provides better understanding of the effect of RH fluctuations on strain which will ultimately lead to more insight into the degradation process of historical tapestries. The paper demonstrates the potential for using DIC as a condition monitoring tool

Strain monitoring of tapestries: results of a three-year research project

The outcomes of an interdisciplinary research project between conservators and engineers investigating the strain experienced by different areas of a tapestry are described. Two techniques were used: full-field monitoring using digital image correlation (DIC) and point measurements using optical fibre sensors. Results showed that it is possible to quantify the global strain across a discrete area of a tapestry using DIC; optical fibre and other sensors were used to validate the DIC. Strain maps created by the DIC depict areas of high and low strain and can be overlaid on images of the tapestry, creating a useful visual tool for conservators, custodians and the general public. DIC identifies areas of high strain not obvious to the naked eye. The equipment can be used in situ in a historic house. In addition the work demonstrated the close relationship between relative humidity and strain

Applications of polymer optical fibre grating sensors to condition monitoring of textiles

Fibre Bragg gratings (FBGs) in polymer optical fibres (POFs) have been used to measure the strain in a woven textile. FBGs in both POFs and silica optical fibres were attached to a woven textile specimen, and their performance characterised. It was demonstrated that the POF FBGs provide improved strain transfer coefficients and reduce local structural reinforcement compared to silica FBGs and therefore make a more suitable proposition for textile monitoring

Changing Perceptions into Reality: Fiduciary Standards to Match the American Directors’ Monitoring Function

This paper describes the historical fiduciary obligations of the American outside director and contrasts those obligations with prevailing obligations in today’s environment of the monitoring director. Special attention is devoted to the role of outside directors when their firm is the target of a takeover. In no other context are the demands on the outside director greater and more strain placed on the monitoring model than in the context of a corporate takeover. The final section of this paper examines the relief modern statutory provisions provide to the director and the monitoring functio

Strain gage calibration

A temporary bonding system for accurately predetermining the individual apparent strain curve characteristics of the gages is used, and subsequently employs a computer to watch the apparent strain curves of the individual gages to determine which gages should be used together on transducers. The temporary bonding system requires a test block on which the gages are temporarily bonded, several thermocouples for monitoring temperature, and a data acquisition system for recording apparent strain data. Initially, a group of strain gages are attached to the test block using a bonding agent that disintegrates at high temperatures. The gages are then wired to an appropriate data acquisition and data, collected throughout a predetermined temperature excursion. Once the data is obtained, the test block is heated until the bonding agent disintegrates freeing the gages from the test block. The gages are then disconnected from the data acquisition system and cleaned, thereby ready for use on transducers

Strain evolution in GaN Nanowires: from free-surface objects to coalesced templates

Top-down fabricated GaN nanowires, 250 nm in diameter and with various heights, have been used to experimentally determine the evolution of strain along the vertical direction of 1-dimensional objects. X-ray diffraction and photoluminescence techniques have been used to obtain the strain profile inside the nanowires from their base to their top facet for both initial compressive and tensile strains. The relaxation behaviors derived from optical and structural characterizations perfectly match the numerical results of calculations based on a continuous media approach. By monitoring the elastic relaxation enabled by the lateral free-surfaces, the height from which the nanowires can be considered strain-free has been estimated. Based on this result, NWs sufficiently high to be strain-free have been coalesced to form a continuous GaN layer. X-ray diffraction, photoluminescence and cathodoluminescence clearly show that despite the initial strain-free nanowires template, the final GaN layer is strained