Papers by Keyword: Creep Deformation

Abstract: The present paper considers the study of creep and deformation properties of sulfur-containing arbolit exposed to various compression stresses. Investigating the creep of lightweight arbolit concretes greatly affecting the performance of bearing and envelope structures draws a special attention during the last years. This issue is of particular relevance in the regions with hot and sharp continental climate. Arbolit concrete is one of the lightest building materials with low thermal conductivity and good soundproof properties. The modern postulates of theory and practice of creation, development of high-strength arbolit concretes on the base of composite sulfur-containing binders have become the methodological framework of the present research. While carrying out scientific research, the following standard measuring and analysis methods of physical and mechanical properties have been used for sulfur-containing arbolit composites. Experimental tests have been implemented on the 28-days samples made of sulfur-containing arbolit, with the cotton plant footstalks as an organic component. The researched samples were vapor sealed with the purpose to eliminate overlapping the processes of contraction and creep. The experimental results have shown that the analysis of prisms deformation in time demonstrates certain derivation from the pattern. Deformation of prisms made of sulfur-containing arbolit loaded at the low stress level were growing at a slower rate that the same deformations at a higher stress level. No derivation has been observed for the prisms of sulfur-containing haydite concrete. For both types of concrete, creep deformation has reached the values exceeding completely recoverable deformation by a factor of 2 or all the samples, the rapid growth of creep deformation has been observed after loading, followed by the gradual slowdown of deformation growth. For sulfur-containing lightweight concretes, as the test shown, the rate of creep deformation growth depends on the hardening curve in time reflecting the process of concrete hardening. This, if compared with sulfur-containing lightweight concretes, creep of sulfur-containing arbolit concrete is significantly lower that eventually leads to the loss of creep deformation at the same stress level. The obtained results can be used when manufacturing an efficient wall material for residential construction, including seismic areas.

Abstract: The creep and rupture test were carried out on a non-standard specimen of 316L stainless steel (316L-SS) diffused bonding joint. And the θ-projection model was used to analyze the minimum creep strain rate and the remaining life at 500°C/6 MPa when the creep strain is 0.2%. According to the test results, design criterion for the diffusion bonding component at high temperature is established. The rupture experimental results show that the remaining life extrapolated by Larsen-Miller equation is relatively consistent with that calculated by the θ project concept method.

Abstract: In design of the electronic device, FEM analyses considering the creep deformation of solder joints in-situ should be conducted to evaluate the strength reliability. The indentation test is one of effective method to evaluate the creep deformation in microscopic region. However, the result obtained by the indentation test does not coincide with that obtained by the tensile creep test. To solve the problem, the method to determine the suitable area for the indentation test had also been proposed by using the numerical test. To apply the proposed method for the actual indentation test, the homogeneity of specimen should be considered. In this paper, the analyses of the proposed indentation tests were conducted by using the homogeneous and inhomogeneous specimen models of Sn-3.0Ag-0.5Cu. Three types of the deformation behavior were given for the initial phase and the indenter was pushed into in the specimen at the three locations. As a result, it was found that there was not difference in the distribution of the principal stress caused by variation in the indent location. However, the proposed method can successfully determine the reference area except for the case when the deformation behaviors of the constituent phases have a large difference.

Abstract: For accurate evaluation of the reliability of electronic package, FEM analyses considering the creep deformation of solder joint in-situ should be conducted. It is well known that the indentation creep test has an advantage to evaluate the creep deformation in microscopic region although there are the problems. Authors already modified the indentation creep test and proposed the method to estimate the steady state creep deformation by the modified test. For lead free solders generally used for the solder joint, the transient creep deformation should be measured by the indentation test in addition to the steady state creep deformation. The transient creep strain occurs in the indentation process. Therefore, it needs to separate the strain into the elastic-plastic strain and the creep strain. In this paper, the method to obtain the stress-strain relation using the indentation test is proposed. New indentation test used the stepped load was proposed to obtained the stress variation during the indenter was pushed and conducted by the numerical test. The suitable measurement point to obtain the relationship between the stress and the strain was identified. The stress variation estimated by proposed area well coincides with the equivalent stress variation of the nodal solution. Therefore, if the method to obtain the strain variation during the indentation process by the indentation in future is developped, it may be possible to estimate the stress-strain curve expressed the uniaxial deformation in the microscopic region.

Abstract: The effect of alloying element (such as Cr, Zr, and Ir) addition on the high-temperature creep deformation behavior of C40/C11_b lamellar-structured (Mo_0.85Nb_0.15)Si₂ silicide crystals was examined. The results indicated that these additions all lead to a decrease in the steady-state creep strain rate (SSCR) when the applied stress is parallel to the lamellar interface. To clarify the origin of this, the dependence of the creep deformation behavior on the microstructure was determined in detail. As a result, it was found that the C40 phase acts as a strengthening phase during the deformation of the C40/C11_b duplex-phase crystals. The variant-1-type C11_b phase grains, whose loading orientation is parallel to [001], also acts as an effective strengthening component. The decrease in SSCR by Cr or Zr addition is attributed to the increase in volume fraction of those C40 phase and C11_b-V1 grains. The refinement of microstructure by Ir addition was also found to result in a modest decrease in the SSCR.

Abstract: In order to investigate fatigue characteristics of nonferrous bolts at elevated temperature, fatigue tests of bolted joints which were tightened with three kinds of nonferrous bolts were been conducted at 100°C atmosphere. The test bolts were made of A5056 aluminum alloy and AZ31 and AZX912 magnesium alloy. Creep tests of the bolts at 100°C atmosphere were also conducted. The results showed that the fatigue limit of A5056 bolt was the highest of all regardless of the ambient temperature. The fatigue limits of AZ31 bolt and AZX912 bolt also were a half of the fatigue limit of A5056 bolt at both ambient temperature. Bolt clamping force losses due to creep deformation were observed for all bolts during fatigue tests at elevated temperature. Hence as additional tests, the creep tests which was controlled either the tensile force or the displacements respectively were conducted. As the results it was seen that the clamping force losses for all bolts were remarkably large although the each creep deformation was different for each bolt material. Therefore the results indicates that we have to pay attention to the clamping force reduction due to creep deformation if we use the nonferrous bolt in high temperature.

Abstract: It has been widely accepted that the creep characteristics at high temperatures are mainly evaluated by a minimum creep rate. Although, a shape of creep curve may vary depending on deformation conditions, the apparent steady state or minimum creep rates be the same. Thus,for detailed analysis and prediction of creep behavior, other values which reflect the shape of each creep curve should be considered. For the purpose, authors have proposed Sato’s strain- acceleration-parameter (Strain Acceleration and Transition Objective index, SATO-index) which reflects strain rate change during creep deformation. Based on the concept of SATO-index, the whole creep curve can be represented by a set of small number of numerical parameters, and can be extrapolated from a part of creep curve. In this paper, application of the concept of SATO-index to the creep curves of aluminum-magnesium solid solutions that the creep behavior of the alloys are well investigated and analyzed. The creep curve can be extrapolated by the concept from transient part of creep curve, and the extrapolated creep rates at the minimum creep rate agree well with experiment. Efficiency of the concept of SATO-index to creep experiments is pronounced.

Abstract: Mechanical property of rock is the main research object of rock mechanics. In order to further learn the rheological characteristics of soft fractured rock mass, the creep test of highly-weathered breccia with different water content of 0.65%, 1.88%, 4.03% using low-intensity uniaxial creepmeter developed by Shandong University is processed, and the strain-time curves under different water conditions and the corresponding variation of creep curves with different stress levels and moisture states are obtained. The experimental results show that the higher water content is, the larger creep deformation is and the longer time of creep deformation reaching stable is, in other words, the influence of water content on the rheological characteristics of rock mass is also significant. Finally, the conclusion that softening critical load (long-term strength) and softening critical depth of soft rock are greatly reduced due to the effect of water on rock structure and mechanical parameters is obtained to provide the fundamental reference for the follow-up tests and similar engineering.

Abstract: Creep behavior of solid solution alloys are reasonably explained by concepts of the “internal and effective stress of high temperature deformation”. The internal stress is considered to be brought by formation of dislocation substructures, and the dislocation structures should have caused long range stress filed in interior of materials. Thus, residual stresses should also be brought by the same origin. In this paper, measurements of the residual stresses after creep deformation by 2D-Xray method are attempt, and the stresses are compared with so-called the “internal stress of high temperature deformation” measured by strain-dip stress-transient test. Although, the stress tensor depends on the deformation condition, the relation with the applied stress show complex manner at a glance. The maximum principal stresses, however, show relatively smaller than the applied stress, and fairly agree with that measured by strain-dip stress-transient technique. Importance of further considerations of the origin of so-called internal stresses is suggested.

Abstract: In order to study the deformation of super-long structures under the influence of creep , take fully advantage of orthogonal design to make nine series reinforced concrete beams of shrinkage-compensating to deeply analyze the function performanced by creep of the reinforced concrete structure and obtain that the time-deflection curves of volume deformation and creep deformation of shrinkage-compensating reinforced concrete beams. The results show that the creep of beams develops rapidly early and the slow development of the late. The greater the expansion stress is in the early, the greater the shrinkage strain in the late, the greater the deformation of volume. So, the appropriate mixing ratio of expansive agent is given by the experiment. It provides a scientific basis for seamless design of super-long structures.