Study of the plastic behavior around the crack tip by means of thermal methods

AbstractIn this work, the behaviour of two cracked stainless steel AISI 410 and C3FM was studied by means of a new procedure based on thermographic methods. A temperature model in time domain was considered in order to obtain information about the first and the second order harmonic of the temperature signal. Interesting results were obtained in term of possibility to describe the plastic phenomena at the crack tip

New data analysis to evaluate defects in composite materials using microwaves thermography

Abstract In this work microwave sources were used as heating sources to evaluate the damages areas in composite materials using thermographic techniques. In particular, lock-in thermography and microwave lock-in thermography tests were carried out on CFRP damaged specimens. A new data analysis was developed to processing the thermographic data obtained by microwave tests and various algorithm were used to processing lock-in thermography tests. Data obtained were compared with non destructive tests performed with other techniques such as x-ray. A numerical model was developed for microwave heating simulation

Improved properties of TiAlN coatings through the multilayer structure

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Effects of Anacetrapib in Patients with Atherosclerotic Vascular Disease

BACKGROUND: Patients with atherosclerotic vascular disease remain at high risk for cardiovascular events despite effective statin-based treatment of low-density lipoprotein (LDL) cholesterol levels. The inhibition of cholesteryl ester transfer protein (CETP) by anacetrapib reduces LDL cholesterol levels and increases high-density lipoprotein (HDL) cholesterol levels. However, trials of other CETP inhibitors have shown neutral or adverse effects on cardiovascular outcomes. METHODS: We conducted a randomized, double-blind, placebo-controlled trial involving 30,449 adults with atherosclerotic vascular disease who were receiving intensive atorvastatin therapy and who had a mean LDL cholesterol level of 61 mg per deciliter (1.58 mmol per liter), a mean non-HDL cholesterol level of 92 mg per deciliter (2.38 mmol per liter), and a mean HDL cholesterol level of 40 mg per deciliter (1.03 mmol per liter). The patients were assigned to receive either 100 mg of anacetrapib once daily (15,225 patients) or matching placebo (15,224 patients). The primary outcome was the first major coronary event, a composite of coronary death, myocardial infarction, or coronary revascularization. RESULTS: During the median follow-up period of 4.1 years, the primary outcome occurred in significantly fewer patients in the anacetrapib group than in the placebo group (1640 of 15,225 patients [10.8%] vs. 1803 of 15,224 patients [11.8%]; rate ratio, 0.91; 95% confidence interval, 0.85 to 0.97; P=0.004). The relative difference in risk was similar across multiple prespecified subgroups. At the trial midpoint, the mean level of HDL cholesterol was higher by 43 mg per deciliter (1.12 mmol per liter) in the anacetrapib group than in the placebo group (a relative difference of 104%), and the mean level of non-HDL cholesterol was lower by 17 mg per deciliter (0.44 mmol per liter), a relative difference of -18%. There were no significant between-group differences in the risk of death, cancer, or other serious adverse events. CONCLUSIONS: Among patients with atherosclerotic vascular disease who were receiving intensive statin therapy, the use of anacetrapib resulted in a lower incidence of major coronary events than the use of placebo. (Funded by Merck and others; Current Controlled Trials number, ISRCTN48678192 ; ClinicalTrials.gov number, NCT01252953 ; and EudraCT number, 2010-023467-18 .)

Application of thermal methods for characterization of steel welded joints

Despite the large number of proposals in the field of fatigue prediction of welded joints, a globally accepted and unified theory, which applies easily to any load condition, does not exist. Real life components, indeed, differ in geometry and/or type of load from the structural design for which they are regarded by Standards, so that a lot of precautionary safety factors are used that lead to an underestimation of the actual fatigue life of joints. Infrared thermography has a great potential in this field, both from structural and thermomechanical points of view. It enables a full field stress analysis with a sufficient spatial resolution so that the complexity of the stress state at the weld toe and its time evolution are taken into account, emphasizing anomalies that may predict structural failure. A new methods for evaluation fatigue limit damage is presented in this paper and in particular interesting results derived from analysis of the evolution of thermoelastic signal phase. Variations in the value of signal phase indicate a not elastic behaviour and plastic dissipation in the material

Thermoelastic stress analysis of titanium components and simultaneous assessment of residual stress

The thermoelastic effect describes a linear relationship between change in body temperature and state of stress in the presence of adiabatic conditions. This approach considers the material properties constant with temperature, which is not correct for all materials. Experimental results and a review of the theory, especially for the titanium and some alloys of aluminium, have shown that the thermoelastic signal is also dependent of mean stress of the material. The use of titanium in various fields of application makes interesting use of thermoelastic technique as full field stress analysis technique. However, it is necessary to make a correction of the measure in relation to the mean stress. The possibility to measure the mean stress allows also an evaluation of residual stresses on the surface of titanium components

A Quantitative Analysis of the Thermoelastic Effect in CFRP Composite Materials

In this study the thermoelastic signal from carbon fibre-reinforced plastic (CFRP) laminates is investigated. A comparison between the theoretical and experimental values of the thermoelastic signal is reported, with the theoretical predictions obtained from two different quantitative models. These models are based on the classic thermoelastic effect law extended to the case of orthotropic materials (by using the mesomechanical or bulk approach), and the modified law assuming that the surface resin-rich layer behaves as a strain witness of the laminate. It is found that the theoretical predictions of the two models can be strongly and differently influenced by the intrinsic orthotropy of carbon fibres. Some effects are highlighted in particular such as the influence of the laminate lay-up and the strong mismatch between the thermal expansion coefficients of the polymer matrix and the fibres. These influences are investigated analytically, predicting the thermoelastic signal from various lay-ups and using strain-based and stress-based analytical models. Experimental evidence of some theoretical findings is provided by reporting on tests performed on CFRP tensile samples manufactured from low-crimp unidirectional fabrics

Thermoelastic stress analysis of titanium components and simultaneous assessment of residual stress

The thermoelastic effect describes a linear relationship between change in body temperature and state of stress in the presence of adiabatic conditions. This approach considers the material properties constant with temperature, which is not correct for all materials. Experimental results and a review of the theory, especially for the titanium and some alloys of aluminium, have shown that the thermoelastic signal is also dependent of mean stress of the material. The use of titanium in various fields of application makes interesting use of thermoelastic technique as full field stress analysis technique. However, it is necessary to make a correction of the measure in relation to the mean stress. The possibility to measure the mean stress allows also an evaluation of residual stresses on the surface of titanium components

A quantitative investigation on the thermoelastic effect of cfrp laminates

The thermoelastic effect on CFRP laminates with various lay-ups is investigated. A thick low crimp unidirectional fabric reinforcement is adopted. The measured thermoelastic signal is compared with predictions from two analytical models based on the meso-mechanical bulk properties of the lamina and on assuming a strain witness behaviour of the surface resin rich layer