Residual strength of unidirectional fibre-metal laminates based on JC toughness of C(T) and SE(B) specimens: comparison with M(T) test results

Fibre‐metal laminates (FMLs) are structural composites designed with the aim of producing very low fatigue crack‐propagation rate, damage‐tolerant and high‐strength materials, if compared to aeronautical Al alloys. Their application in aeronautical structures demands a deep knowledge of a wide set of mechanical properties and technological values, including both fracture toughness and residual strength. The residual strength of FMLs have been traditionally determined by using wide centre‐cracked tension panels M(T). The use of this geometry requires large quantities of material and heavy laboratory facilities. In this work, fracture toughness ( J_C) of some unidirectional FMLs laminates was measured using a recently proposed methodology for critical fracture toughness evaluation on compact tension C(T) and single‐edge bend SE(B) specimens. Additionally, residual strength values of wider M(T) specimens with different widths (W from 150 to 200 mm) and several crack to width ratios (2a/W) were experimentally obtained. Some experimental residual strength values of M(T) specimens (W from 150 to 400 mm and different 2a/W ratios) of Arall were also obtained from the bibliography. Based on J_C results from C(T) and SE(B) specimens, and either using or not using crack‐tip plasticity corrections, the residual strengths of the M(T) specimens were predicted and compared to the experimental ones. The results showed good agreement, especially when crack‐tip plasticity corrections were applied.     

Forward light scatter and contrast sensitivity in keratoconic patients

Purpose

The aim of this study was to obtain intraocular forward light scatter (FLS) data in keratoconus patients and to explore possible relationships with contrast sensitivity.

Method

Intraocular straylight was assessed in the right eye of 10 visually-normal subjects (31 ± 5 years) and 5 keratoconus patients (34 ± 9 years) using the van den Berg straylight meter. Contrast sensitivity was also measured in both groups, with and without a glare source provided by the Brightness Acuity Tester (BAT), using a Pelli-Robson chart. Inclusion criteria for the keratoconic patients were chosen to avoid natural causes of increased scatter and to limit the influence of factors that could affect the straylight measurements.

Results

Intraocular light scatter was significantly greater in the keratoconic patients than in normal subjects for each of the three eccentricities tested (Mann-Whitney U test (2-tailed): Z ≤ −2.2, p ≤ 0.027). Baseline Pelli-Robson contrast sensitivity was also found to be lower in the keratoconus group than in the normal subjects (Mann-Whitney U test: Z = −2.2, p = 0.023). Under glare conditions contrast loss was significantly greater in the keratoconic patients than in the normal subjects (Mann-Whitney U test: Z = −2.5, p = 0.013). High levels of negative correlation were found between the magnitudes of intraocular straylight and baseline contrast sensitivity in the keratoconus group (Spearman's correlation coefficient (R_S) ≤ −0.87, p ≤ 0.027).

Conclusion

The high values of straylight measured in the keratoconic patients cannot be explained by age or scarring and could be related to the structural degradation of the cornea. Further investigation of intraocular scatter in keratoconus is warranted to improve our current understanding of the visual deficits associated with this pathology.     

Effect of switchable glazing on discomfort glare from windows

In this paper we report the results of experimental tests carried out to study the effect of electrochromic (EC)-glazing on discomfort glare from windows. The research is performed by a small scale test-cell equipped with a small area double glazing unit (DGU) where one pane consists of an EC device with a visible transmittance τ_v ranging from about 7 to 70% and the other of an ordinary clear float glass (τ_v ∼ 90%), the overall DGU transmittance dynamic range resulting about 4–58%. The performance of the device is investigated under real sky conditions as a function of time, solar radiation intensity, test-cell orientation and switching strategies (static and dynamic). The evaluation methods adopted for assessing the discomfort glare degree are the “New Daylight Glare Index” (DGI_N) and the “Glare Subjective Rating” (SR). Results deriving from application of these two methods are compatible and show that for south facing windows and under the involved climatic conditions EC-glazing can be very effective in reducing discomfort glare caused by high window brightness originating from diffuse skylight. This glare reduction can be realized without compromising much of the available daylight so without necessarily increasing the need for artificial lighting and, at the same time, preserving an unobstructed outside view. Occurrence of glare effects from west (or east) facing windows is more difficult to be controlled due to the lower sun angles which entail the use of EC devices switchable to very low transmittance states (τ_v < 7%) and/or integration of traditional sun protection devices. This would probably compromise indoor daylight availability (and potential energy savings associated to reduced use of artificial lighting) as well as exterior view although the positive effect of the EC-glazing could be a substantial reduction of the frequency of use of these additional shading systems.     

The position index of a glare source at the borderline between comfort and discomfort (BCD) in the whole visual field

The objective of this study was to propose a new position index for a source located in the whole visual field, including the lower visual field. The sensation of brightness was tested at various positions in the visual field. The Glare Tester especially designed for and used in this experiment had two sources: the standard source located on the line of sight and the test source located at a designated position in the visual field. The boundary of the visual field, BCD luminance on the line of sight, and BCD luminance at various positions in the visual field were measured. The visual field was measured, and the boundaries were approximately 90° temporally, 67° inferiorly, and 50° superiorly. From the measurement of BCD luminance on the line of sight, the BCD luminance was obtained at 2590 cd/m² under the conditions of a source size of 0.0011 sr and background luminance of 34.3 cd/m². In measuring BCD luminance at various positions, the standard source was set to the BCD luminance of each observer, with the luminance of the test source being increased. The observers were asked to stop when the sensation of the test source became equal to that of the standard source. From the results of these measurements, the position index P_i was derived. Finally, a chart for determining the position index P_i was proposed based on the three measurements.     

An Historic Overview of the Development of Fibre Metal Laminates

In this paper a brief overview of the history of Fibre Metal Laminates Arall and Glare is given as background information for the other, technical articles in this journal. The story of the development of Fibre Metal Laminates is rather a unique story in the history of aircraft materials: A university laboratory invented, developed and certified an aircraft material. Many parties were involved naturally, yet the very heart of the activity was the Structures and Materials Laboratory of the Faculty of Aerospace Engineering of Delft University of Technology in The Netherlands. At the break of the world's largest passenger transport aircraft, the Airbus A380, in which a substantial part of the fuselage will be made of Glare, the glass fibre-aluminium version of Fibre Metal Laminates, it is a good moment to tell some of its history.     

Application of the energy release rate approach for delamination growth in Glare

Fatigue crack growth in a fibre metal laminate such as Glare is accompanied by delamination growth at the interface between the aluminium and glass fibre/adhesive layers. To incorporate this delamination growth in crack growth prediction methods, the energy release rate approach is applied to describe the delamination growth rate. Tests were performed to determine the relationship between the delamination growth rate and the calculated energy release rate.     

A first approach to discomfort glare in the presence of non-uniform luminance

This study aims to elucidate the difference in glare sensation between uniform and non-uniform glare sources. In the experiment, the degree of discomfort glare is examined using simulated windows of uniform and non-uniform surface luminance. The window plane is divided into two parts, the upper and lower surfaces, and the luminance and solid angle of each surface are set differently. The upper and lower parts are assumed to be the sky and obstacle, respectively. Two conclusions follow from this study. First, the degree of discomfort glare for the uniform window is higher than it is for the non-uniform window, when the luminance of the uniform window is the same as the average luminance of the non-uniform window. Therefore, the discomfort glare sensation of the non-uniform window is different from that of the uniform window. Second, the glare source in the non-uniform window is restricted by luminance and originates from parts ranging from the highest level of luminance down to a level that is 61% of the highest level of luminance. These results may be useful for selecting the glare source in a window with a non-uniform luminance distribution.     

Development of the nomo-graph for evaluation on discomfort glare of windows

Human beings have been using daylight for a long time. The daylight provides building occupants with psychological stability and also serves as lighting. However, the discomfort glare of windows produced from the daylight could be a severe problem as the working condition is getting more complicated and precise. Although numerous studies have been performed in order to solve this problem, most studies have been performed on Caucasians. The recent studies have revealed that there were differences between Caucasians and Asians in ocular activity, pigmentation, and color sensibility depending on the iris color. These data implies that it is difficult to directly apply the data from studies on the Caucasian to Asians whose physiological properties of eyes are different from those of the Caucasian. Therefore, it is necessary to develop an evaluation method of window discomfort glare, which may represent the visual feature of Asian appropriately. In the present study, we investigated the visual difference between Caucasian and Asians and established the nomo-graph to develop the method appropriate for the evaluation of the window discomfort glare for Asians.     

教室光环境统一眩光值影响因素的研究

研究了标准教室场景中统一眩光值(UGR)的干扰因素,通过DIALux改变输入条件,如灯具的安装位置、反射比、光通量、配光曲线等,同时设置不同的UGR测点位置,经模拟优化,发现UGR并非单一与灯具参数,比如配光曲线、光通量等有关,还与安装的环境参数有关.上照光通量由0增加至与下照光通量相等时,UGR下降19.7％;按照国...     

Evaluating visual comfort and performance of three natural lighting systems for deep office buildings in highly luminous climates

This work, part of a wider study, presents a qualitative and quantitative approach to evaluate daylighting systems for use in office buildings located in latitudes where natural luminous conditions throughout the year are of high solar radiation, as in Israel. Their widespread application in this kind of climate, where the excessive penetration of direct radiation can be a problem, is possible. They can produce a consequent improvement of working conditions and energy savings, yet this is not the case now.