Measurement of the in situ transverse tensile strength of composite plies by means of the real time monitoring of microcracking

Failure of a ply due to transverse loading is one of the mechanisms that was taken into account in physically-based failure criteria, used in composites design. However, experimental data are scarce and the measurement techniques used in the past are time consuming and involve a lot of specimen handling during testing. While some physical information is currently well consolidated (such as the dependence of the strength on ply thickness, or in situ strength), there still remain relevant open questions. This work presents a methodology, which does not interfere with the tensile test, to detect transverse cracks by optical means. Four different configurations of CFRP are considered. The results show that the in situ strength depends on the thickness of the ply and the orientation of the adjacent layers. In the case of thick transverse plies, the strength is controlled by full-width transverse cracks whereas, in thin plies cracking parallel to the specimen’s mid-plane occurs before transverse matrix cracking.     

几种典型目标体外形的高频回声特性研究

本文研究常见、典型的水中目标体外形的回声特性是目标回声特性研究的基础内容。采用基于Kirchhoff近似的平面元方法和几何建模软件相结合的数值方法计算研究了三种典型外形的收发合置的目标强度。通过对计算结果的对比分析,归纳得到了一些高频回声规律。     

水泥土搅拌桩桩身均匀性定量判定与评价方法

介绍一种用定量指标判定与评价水泥土搅拌桩桩身均匀性的方法。     

Use of melatonin in recovery from jet-lag following an eastward flight across 10 time-zones

Subjective, physiological and physical performance variables are affected following travel across multiple time-zones (jet-lag). The objective of the study was to examine the effects of oral melatonin in alleviating jet-lag by investigating its effects on subjects who had flown from London to Eastern Australia, 10 time-zones to the east. Melatonin (5 mg day^?1) or placebo capsules were administered to 14 experimental (13 males and 1 female) and 17 control subjects (15 males and 2 females), respectively, in a double-blind study; the time of administration was in accord with the current consensus for maximizing its hypnotic effect. Grip strength and intra-aural temperature were measured on alternate days after arrival at the destination, at four different times of day (between the times 07:00 – 08:00 h, 12:00 13:00 h, 16:00 – 17:00 h and 19:00 – 20:00 h local time). In addition, for the first 6 – 7 days after arrival in Australia,subjective ratings of jet-lag on a 0- 10 visualanalogue scale and responses to a Jet-lag Questionnaire (incorporating items for tiredness, sleep, meal satisfaction and ability to concentrate) were recorded at the above times and also on retiring (at about midnight). Subjects continued normally with their work schedules between the data collection times. Subjects with complete data (13 melatonin and 13 placebo subjects), in comparison with published data, showed partial adjustment of the diurnal rhythm in intra-aural temperature after 6 days. A time-of-day effect was evident in both right and left grip strength during adjustment to Australian time; there was no difference between the group taking melatonin and that using the placebo. Right and left grip strength profiles on day 6 were adjusted either by advancing or delaying the profiles, independent of whether subjects were taking melatonin or placebo tablets. Subjects reported disturbances with most measures in the Jet-lag Questionnaire but, whereas poorer concentration and some negative effects upon sleep had disappeared after 3 – 5 days, ratings of jet-lag and tiredness had not returned to ‘zero’ (or normal values), respectively, by the sixth day of the study. Subjects taking melatonin showed no significant differences from the placebo group in perceived irritability, concentration, meal satisfaction, ease in getting to sleep and staying asleep, frequency of bowel motion and consistency of the faeces. These results suggest that, in subjects who, after arrival, followed a busy schedule which resulted in frequent and erratic exposure to daylight, melatonin had no benefit in alleviating jet-lag or the components of jet-lag, and it did not influence the process of phase adjustment.     

Force exertion in awkward working postures-strength capability while twisting or working overhead

Isometric strength data have been collected for three of the awkward work situations often imposed by workplace constraints in industry, as found in jobs such as maintenance and repair. The effects of the task layout factors (location of the workpiece, reach distance and direction of force exertion) were investigated and the data has been tabulated to show the degree to which strength may be reduced in different situations. Strength measurements in the present study were found to be considerably higher than previous measurements, apparently due to differences in instructions on foot placement that were given to subjects, which indicates that even small constraints on posture within the workplace may have large effects on the ability to exert force.     

Modelling of the strength–porosity relationship in glass-ceramic foam scaffolds for bone repair

Foam-like glass-ceramic scaffolds based on three different glass compositions (45S5 Bioglass and two other experimental formulations, CEL2 and SCNA) were produced by sponge replication and characterized from morphological, architectural and mechanical viewpoints. The relationships between porosity and compressive or tensile strength were systematically investigated and modelled, respectively, by using the theory of cellular solids mechanics or quantized fracture mechanics. Models results are in good agreement with experimental findings, which highlights the satisfactory predictive capabilities of the presented approach. The developed models could contribute to improve the rational design of porous bioceramics with custom-made properties. Knowing the scaffold recommended strength for a specific surgical need, the application of the models allows to predict the corresponding porosity, which can be tailored by varying the fabrication parameters in a controlled way so that the device fulfils the desired mechanical requirements.     

Geopolymers based on a coarse low-purity kaolin mineral: Mechanical strength as a function of the chemical composition and temperature

A coarse mineral with 70% kaolinite and 30% quartz was calcined and chemically activated by alkaline solutions of Na₂SiO₃ and NaOH. The compressive strength evolution was investigated as a function of the curing temperature at 20 and 80 °C, and the molar ratios of SiO₂/Al₂O₃ (2.64-4.04) and Na₂O/Al₂O₃ (0.62-1.54). For curing at 20 °C, the best composition was SiO₂/Al₂O₃ = 2.96 and NaO/Al₂O₃ = 0.62, reaching 85 MPa at 28 days. Curing at 80 °C had a positive effect on the strength development only in the first 3 days. X-ray diffraction of the geopolymeric formulations showed the formation of amorphous silicoaluminates of similar nature. The microstructure consisted of unreacted quartz and metakaolinite particles in a matrix of silicoaluminate polymer and condensed silica gel from the unreacted sodium silicate.     

Effect of thermomechanical treatment on microstructure and mechanical properties of AISI 301LN stainless steel

Abstract

A wide range of cold thickness reduction (10–80%) and subsequent annealing were carried out on AISI 301LN stainless steel. X-rays and Feritscope MP30 were used to identify the strain induced α′-martensite phase and its volume fraction respectively. The microstructure was observed by optical micrograph and scanning electron microscope. The results show that shear bands were present and strain induced α′-martensite nucleated at their intersections. The volume fraction of α′-martensite increased with the increased cold reduction by the continuous growth of embryos, which resulted in the increasing yield and tensile strength. The reversion of α′-martensite to austenite occurred after subsequent annealing. The grain size variation of austenite was related to the annealing regime. A good combination of strength and ductility can be obtained after annealing at 650°C for 30 min. The effect of grain size on yield strength conformed with the Hall–Petch relationship in the entire range of our analysis.     

The behaviour of pin-ended flange elements in compression

Stowell's solution [1] for the buckling behaviour of flange elements in compression was premised on the assumption that the element was fixed against flexural rotations at the ends, a condition representing relatively thick elements for which the thickness dimension is adequate to prevent rotations. This paper presents a solution similar to Stowell's which is applicable to pin-ended flange elements. Aspects not considered in Stowell's work, such as the use of elliptic functions to describe the gradual change of mode shape from sinusoidal to essentially linear, and the gradual and asymptotic changes in axial rigidity in the post-buckling range are described in the paper. The paper also presents comparisons between the behaviour of pin-ended and fixed-ended flange elements. Finally, simple strength equations for flange elements in uniform compression based on the first yield criterion are derived.