Validation of in situ applicable measuring techniques for analysis of the water adsorption by stone

As the water adsorbing behaviour (WAB) of stone is a key factor for most degradation processes, its analysis is a decisive aspect when monitoring deterioration and past conservation treatments, or when selecting a proper conservation treatment. In this study the performance of various non-destructive methods for measuring the WAB are compared, with the focus on the effect of the variable factors of the methods caused by their specific design. The methods under study are the contact-sponge method (CSM), the Karsten tube (KT) and the Mirowski pipe (MIR). Their performance is compared with the standardized capillary rise method (CR) and the results are analysed in relation to the open porosity of different lithotypes. Furthermore the effect of practical encumbrances which could limit the application of these methods was valuated. It was found that KT and CSM have complementary fields of investigation, where CSM is capable of measuring the initial water uptake of less porous materials with a high precision, while KT was found commodious for measuring longer contact times for more porous lithotypes. MIR showed too many discommodities, leading to unreliable results. To adequately compare the results of the different methods, the size of the contact area appears to be the most influential factor, whereas the contact material and pressure on the surface do not indicate a significant influence on the results. The study of these factors is currently being extended by visualization of the water adsorption process via X-ray and neutron radiography in combination with physico-mathematical models describing the WAB

Creep-fatigue life assessment of cruciform weldments using the linear matching method

This paper presents a creep-fatigue life assessment of a cruciform weldment made of the steel AISI type 316N(L) and subjected to reversed bending and cyclic dwells at 550C using the Linear Matching Method (LMM) and considering different weld zones. The design limits are estimated by the shakedown analysis using the LMM and elastic-perfectly-plastic material model. The creep fatigue analysis is implemented using the following material models: 1) Ramberg-Osgood model for plastic strains under saturated cyclic conditions; 2) power-law model in “time hardening” form for creep strains during primary creep stage. The number of cycles to failure N? under creep-fatigue interaction is defined by: a) relation for cycles to fatigue failure N dependent on numerical total strain range "tot for the fatigue damage !f ; b) long-term strength relation for the time to creep rupture t dependent on numerical average stress ¯ during dwell t for the creep damage !cr; c) non-linear creep-fatigue interaction diagram for the total damage. Numerically estimated N? for different t and "tot shows good quantitative agreement with experiments. A parametric study of different dwell times t is used to formulate the functions for N? and residual life L? dependent on t and normalised bending moment ˜M , and the corresponding contour plot intended for design applications is created

Review of creep deformation and rupture mechanism of P91 alloy for the development of creep damage constitutive equations under low stress level

This paper presents a review of creep deformation and rupture mechanism of P91 alloy for the development of its creep damage constitutive equations under lower stress level. Creep damage is one of the serious problems for the high temperature industries and computational approach (such as continuum damage mechanics) has been developed and used, complementary to the experimental approach, to assist safe operation. However, there are no ready creep damage constitutive equations to be used for prediction the lifetime for this type of alloy, partially under low stress. The paper reports a critical review on the deformation and damage evolution characteristics of this alloy, particularly under low stress, to form the physical base for the development of creep damage constitutive equations. It covers the influence of the stress level, states of stress, and the failure criterion

The development of advanced creep constitutive equations for high chromium steel P91 at low stress range

Diffusion dominates the creep deformation at low stress range for high chromium steel P91. Brittle creep fracture is caused by cavity nucleation, growth and coalescence of cavities and large precipitates (Laves phase and M23C6) at grain boundary under low stress range. At low stress range, a linear relation between strain at failure and different stresses has been described. Moreover, the minimum strain rate is also proportional to the different stresses

Estimation of Low-Cycle Fatigue Curves of High-Strength and Welded Steel 10CrNi3MoV

In this work is tested applicability of the extended uniform material law for high-strength steel on 10CrNi3MoV steel and its weld. Predicted low-cycle fatigue curves differ significantly from the measurements. Despite the reported scientific effort to predict fatigue properties numerically, results show that strain controlled fatigue tests must be conducted for determination of fatigue properties in the praxis.V tejto práci je testovaná využiteľnosť rozšíreného zjednocujúceho pravidla pre vysokopevnostnú oceľ 10CrNi3MoV a jej zvarok. Predpovedané nízkocyklové krivky únavovej životnosti sa líšia podstatne od meraní. Napriek zdokumentovanému vedeckému úsiliu pri predikcii únavových charakteristík výpočtovo, výsledky ukazujú, že deformačne riadené únavové skúšky sa musia vykonať pre stanovenie únavových charakteristík v praxi

Experimental and numerical analysis of a helical spring failure

Results of experimental and numerical analysis of a broken motor vehicle helical spring are presented in this paper. Location of the fracture is on a first active coil of the spring. Experimental part of the research employed optical microscopy that revealed fractured surface microstructure and allowed for detection of inclusions. Corroded fracture surface limited scanning electron microscopy examination (SEM). Nevertheless, corrosion pits on the edge of the spring wire which served as crack initiation points could be detected by SEM along with radiating ridges left by the fracture front that propagated to the opposite edge of the wire. Optical emission spectrometer with glow discharge source sample stimulation was used to determine material chemical composition that is adequate to spring steel 61SiCr7. Additionally, hardness test was performed and obtained value was used to derive maximum tensile strength of the steel. Experimentally collected data served as input for numerical analysis of helical spring. Finite element analysis of a helical spring model was performed. Stress distribution was determined and fatigue life of the undamaged helical spring predicted. Results were compared with those obtained analytical. Causes of failure are outlined assessing the results of the performed experimental and numerical analysis. Insufficient corrosion protection and excessive contact between the coils caused damage that developed from initial crack to final fracture of the spring. Results obtained by this research are valuable in understanding fracture behavior of helical spring mounted in suspension system of various motor vehicles. Given the presented results, further improvements of spring design can be made in order to reduce failures

Fracture toughness testing data: A technology survey

Technical abstracts for about 90 significant documents relating to fracture toughness testing for various structural materials including information on plane strain and the developing areas of mixed mode and plane stress test conditions are presented. An overview of the state-of-the-art represented in the documents that have been abstracted is included. The abstracts in the report are mostly for publications in the period April 1962 through April 1974. The purpose of this report is to provide, in quick reference form, a dependable source for current information in the subject field