Tensile Creep Tests Research Articles

A thermodynamically consistent constitutive model for diffusion-assisted plasticity in Ni-based superalloys

An elasto-viscoplastic thermodynamically consistent constitutive model for diffusion-assisted phase transformations is presented here. The model accounts for the different deformation mechanisms, their time dependence, the crystal rotations produced by microtwin propagation and the chemistry-plasticity coupling occurring at high temperature. It is applied to the study of the chemically assisted microtwinning observed in Ni-based superalloys in the temperature range of 600–800 °C. The model parameters are calibrated against multi-directional mechanical data from tensile creep tests of single crystal superalloy MD2. The constitutive model is then implemented into a crystal plasticity finite element code to study the activation of the different deformation mechanisms within single crystal and polycrystalline aggregates. Doing so, a relation between the rotations of the crystal and the creep life of the different crystal orientations is established. The results eventually reveal the critical role of the strong anisotropy of microtwin formation on the asymmetric behavior of the alloy and its relevant role on the mechanical performance.

Influence of relative humidity on tensile and compressive creep of concrete amended with ground granulated blast-furnace slag

This paper presents an experimental study on the influence of ambient relative humidity on tensile creep of plain concrete amended with Ground Granulated Blast-furnace Slag and compares it with its influence on compressive creep. Tensile and compressive creep tests were carried out on concrete specimens of 34.49MPa compressive strength and 0.56 water/binder ratio at 51, 68 and 100% relative humidity. The results show a linear relationship between compressive creep and relative humidity; this cannot be said about tensile creep. Tensile creep was observed to be more sensitive to change in ambient humidity than compressive creep. Based on equal applied stress, tensile creep was found to be several times higher than compressive creep and the difference was greater in drying creep than in basic creep. On the basis of equal stress/strength ratio, tensile-to-compressive creep ratio was slightly less than 1 for drying creep and much less for basic creep. http://dx.doi.org/10.4314/njt.v37i1.3

Structure analysis and enhancement of creep resistance and thermal properties of eutectic Sn-Ag lead free solder alloy by Ti and Cd - addition

Eutectic (Sn-3.5wt.%Ag) solder alloy is used in electronic circuits in which the creep property of the solder joints is essential for their applications. The study of creep, structure and thermal properties of three solder alloys (Sn-3.5wt.%Ag,Sn-3.5wt.%Ag-0.27wt.%Ti and Sn-3.5wt.Ag-0.27wt.%Cd) is characterized by the presence of (Ag3Sn-IMC) beside the phase (β-Sn). The microstructure parameters obtained from the X-ray analysis represented by, lattice parameters (a, c), the axial ratio (c/a), the residual strains (Δa/a0, Δc/c0) and peak height intensities (hkl) of some crystallographic planes are given. All parameters were found to be sensitive to the additions of (Ti or Cd), applied stresses and working temperatures in the range (298-373K).The crystallite size of the (211) reflection was found to increase from (61-132nm) with the additions and to decrease from (115-79nm) with the working temperatures. The morphological studies show a remarkable decrease in the size of (β-Sn) grains with the addition of (Cd) content which confirms the X-ray data. The obtained results show a decrease in melting temperature with the additions. The creep properties are notably improved by the addition of either (Ti) or (Cd). In order to reveal the creep characteristics such as stress exponent (n) and activation energy (Q), the tensile creep tests were performed within the temperature range (298-373K) at constant applied stress (17.27MPa). Based on the obtained stress exponents and activation energies, it is explained that the dominant deformation mechanism is dislocation climb over all temperature range.

Tensile-Creep Test Specimen Preparation Practices of Surface Support Liners

Ground support has always been considered as a challenging issue in all underground operations. Many forms of support systems and supporting techniques are available in the mining/tunnelling industry. In the last two decades, a new polymer based material, Thin Spray–on Liner (TSL), has attained a place in the market as an alternative to the current areal ground support systems. Although TSL provides numerous merits and has different application purposes, the knowledge on mechanical properties and performance of this material is still limited. In laboratory studies, since tensile rupture is the most commonly observed failure mechanism in field applications, researchers have generally studied the tensile testing of TSLs with modification of American Society for Testing and Materials (ASTM) D-638 standards. For tensile creep testing, specimen preparation process also follows the ASTM standards. Two different specimen dimension types (Type I, Type IV) are widely preferred in TSL tensile testing that conform to the related standards. Moreover, molding and die cutting are commonly used specimen preparation techniques. In literature, there is a great variability of test results due to the difference in specimen preparation techniques and practices. In this study, a ductile TSL product was tested in order to investigate the effect of both specimen preparation techniques and specimen dimensions under 7-day curing time. As a result, ultimate tensile strength, tensile yield strength, tensile modulus, and elongation at break values were obtained for 4 different test series. It is concluded that Type IV specimens have higher strength values compared to Type I specimens and moulded specimens have lower results than that of prepared by using die cutter. Moreover, specimens prepared by molding techniques have scattered test results. Type IV specimens prepared by die cutter technique are suggested for preparation of tensile test and Type I specimens prepared by die cutter technique should be preferred for tensile creep tests.

Influence of Ingot and Powder Metallurgy Production Route on the Tensile Creep Behavior of Mo–9Si–8B Alloys with Additions of Al and Ge

Refractory metals and their alloys show potential for high temperature applications, due to the elevated melting points often paired with very good creep resistance. Spark plasma sintering (SPS) as well as arc‐melting is used here to prepare quaternary and quinternary Mo–9Si–8B–xAl–yGe (x is 0 or 2; y is 0 or 2, all numbers in at%) samples. All samples consist of a Mo solid solution (Moss) and two intermetallic phases: Mo3Si (A15) and Mo5SiB2 (T2). Aluminum and germanium reduce the melting point and slightly decrease the density of the material. The specimens are homogenized and coarsened by a subsequent heat‐treatment in vacuum at 1850 °C for 24 h. The resulting microstructure is investigated using scanning electron microscope (SEM), energy‐dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), X‐ray fluorescence spectroscopy (XRF), and inductively coupled plasma optical emission spectrometry (ICP‐OES) analysis. A vacuum creep testing device for small tensile creep specimens is presented. It is heated by graphite radiation heaters usable up to 1500 °C in vacuum of 2 · 10‐4 Pa with an oil diffusion pump. Tensile creep tests are performed at 1250 °C and stresses from 50 MPa up to 250 MPa. Specimens produced by ingot metallurgy feature superior creep properties compared to powder metallurgy samples.

Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe

The microstructure and creep behaviour of the welded joints of P92 steel pipe were investigated in order to determine the influence of orbital heat welding technology on the creep resistance. Creep specimens were machined from the welded joints. Tensile creep tests of welded joints were performed at 873 K using different stresses. The microstructure of tested specimens was investigated by scanning electron microscope Tescan equipped with an electron-back scatter diffraction. The creep results showed that the creep fracture strain of the welded joints decreases with decreasing value of applied stress. Microstructure investigation showed that fracture behaviour of welded joints is influenced by an enhanced cavity formation at grain boundaries in the heat-affected zone causing lower fracture ductility.

Tensile creep of miniaturized specimens

Abstract

Time-temperature-aging-depth shift functions for dynamic modulus master curves of asphalt mixtures

Oxidative aging is one of the significant environmental effects on asphalt pavement performance. This study aims to characterize the aging viscoelastic property of asphalt mixtures such as dynamic modulus at different aging times and pavement depths, then develops two aging shift functions to account for the effects of long-term aging and non-uniform field aging in the pavement depth. Tensile creep test and direct tension test are conducted on 12 laboratory-mixed-laboratory-compacted (LMLC) asphalt mixtures with three laboratory aging times and 16 field-aged asphalt mixtures with four field aging times, respectively. The dynamic modulus of LMLC mixtures is determined from the tensile creep test and the elastic–viscoelastic correspondence principle is utilized to obtain the dynamic modulus of field-aged asphalt mixtures from the direct tension test. The dynamic modulus master curves of the asphalt mixtures at different aging times and pavement depths are constructed using the modified Christensen-Anderson-Marasteanu (CAM) model. It is shown that both of the rheological index and glassy modulus increase with aging time and the crossover frequency decreases with aging time. The long-term aging shift function is determined as a function of aging time, acceleration factor, activation energy, and aging temperature. The depth shift function is determined as a function of pavement depth. With the aid of the two aging shift functions, it becomes possible to construct a single dynamic modulus master curve after taking into account the effects of temperature, long-term aging, and non-uniform aging with pavement depth below the surface.

Creep deformation and rupture behaviour of service exposed P91 weld and base steel measured by miniature tensile creep testing

Early cracking had occurred at a weld joint of a service-exposed P91 steel hot reheat pipe branch. In this study, a series of miniature tensile creep tests were conducted for both the base and weld materials extracted from the retired P91 pipe weld. Tests were conducted at various stress levels at 569 °C to measure the creep properties and investigate the failure mechanisms. Microstructural analyses were also carried out for post-test specimens. The measured creep strengths were represented in terms of the Larson-Miller parameter, and compared to literature data. Most of the data fell within the 95% error band of grade 91 steel. However, the weld metal exhibited higher creep rupture strengths. It showed creep brittle fracture, and base metal showed creep ductile behaviour. The weld metal sometimes had non-uniform microstructures, yielding a seriously tempered zones with minor tempered martensites, thereby causing early creep ductile failure of the weld.

Transmission electron microscopy study of the microstructural evolution during high-temperature and low-stress (011) [11] shear creep deformation of the superalloy single crystal LEK 94

Abstract

Small punch and uniaxial creep fracture behaviours of modified SUS304H steel at various temperatures

Commercial austenitic stainless steel SUS304H with small amount of vanadium addition was used in this study. Small punch (SP) creep and uniaxial tensile creep tests were conducted at 650, 700, and 750 °C to measure creep lives and the minimum displacement rates or the minimum creep strain rates. The measured parameters were compared between the two test methods, seeking empirical relationships among the parameters using Larson-Miller Parameter and Monkman-Grant relation. Magnitude of the applied stress (MPa) in the uniaxial tensile creep test was approximately equal to the applied load value (N) in the SP creep test at all test temperatures. It was shown that during the creep deformation of the SP creep specimen, crack initiation and accompanying crack growth occur simultaneously. Competing failure mechanisms of creep deformation and crack growth may affect the SP creep life and consequently determine the proportionality function, α, in the relation between the SP load and the tensile creep rupture stress in creep tests.

Effect of sustained loading and environmental conditions on the creep behavior of an epoxy adhesive for concrete structures strengthened with CFRP laminates

Abstract In this paper, the creep behavior of a structural epoxy adhesive used for strengthening Reinforced Concrete (RC) structures with Carbon Fiber Reinforced Polymer (CFRP) laminates is studied through an experimental program. Long-term tensile creep tests were carried out inside a climate chamber using sustained loading levels, temperature and humidity as the parameters for the study. The specimens were kept loaded inside the climate chamber for 1000 h. Standard Tensile Tests (STT), Dynamic Mechanical Analysis (DMA) and Differential Scanning Calorimetry (DSC) tests were carried out to characterize the adhesive used. In general, the results obtained revealed that changing temperature and humidity conditions greatly affect not only instantaneous and creep strain values, but also time to failure, leading to a change in the overall behavior of the adhesive.

Enhancing the microstructure and tensile creep resistance of Sn-3.0Ag-0.5Cu solder alloy by reinforcing nano-sized ZnO particles

Sn-Ag-Cu lead-free solders are regarded as a potential substitute for Pb-Sn solder alloys. In the current study, the non-reacting, non-coarsening ZnO nano-particles (ZnO NPs) were successfully incorporated into Sn–3.0Ag–0.5Cu (SAC305) lead-free solder by mechanical mixing of ZnO powders and melting at 900°C for 2h. Tensile creep testing was performed for plain SAC305 solder and SAC305-0.7wt% ZnO NPs composite solders and a Garofalo hyperbolic sine power-law relationship was created from the experimental data to predict the creep mechanism as a function of tensile stress and temperature. Based on the tensile creep results, the creep resistance of SAC305 solder alloy was improved considerably with ZnO NPs addition, although the creep lifetime was increased. From microstructure observation, reinforcing ZnO NPs into SAC305 solder substantially suppressed the enlargement of Ag3Sn and Cu6Sn5 intermetallic compound (IMC) particles and decreased the spacing of the inter-particles between them, reduced the grain size of β-Sn and increased the eutectic area in the alloy matrix. The modification of microstructure, which leaded to a strong adsorption effect and high surface-free energy of ZnO NPs, could result in hindering the dislocation slipping, and thus provides standard dispersion strengthening mechanism. Moreover, the average activation energy (Q) for SAC305 and SAC305-0.7ZnO alloys were 50.5 and 53.1kJ/mol, respectively, close to that of pipe diffusion mechanism in matrix Sn.

Material Characterization and Low Cycle Fatigue Model of Low Ag Content Lead-Free Solder

In this paper, a method of design-for-reliability for the advanced electronic package under temperature cycling (TC) condition is demonstrated, including material characterization, reliability test, finite element analysis (FEA), and fatigue life model development. Tensile tests are conducted for Sn–1.0Ag–0.5Cu–0.02Ni (SAC105Ni0.02) solder alloy at four stain rates of $10^{{-5}}$ , $10^{{-4}}$ , $10^{{-3}}$ , and $10^{{-2}}$ and four test temperatures of − 35°C, 25 °C, 75 °C, and 125 °C to develop temperature- and strain rate-dependent material models. Tensile creep tests are carried out at various temperatures and stress levels to study creep behavior. TC reliability test is conducted for ball grid array package with SAC105Ni0.02 solder joints. Thermal fatigue lives are obtained from TC test with different failure rates. FEA simulation is carried out for each package using the developed mechanical properties and creep model of the solder. Fatigue life models with different failure rates are proposed for the SAC105Ni0.02 solder by combining simulation results and experimental data. Fatigue resistance of the SAC105Ni0.02 solder is comparable with that of high Ag content SAC solders.

Accelerated Tests for Lifetime Prediction of PE‐HD Pipe Grades

SummaryPipe failure in long‐term applications is characterized by creep crack initiation and creep crack growth. Both can be determined by fracture mechanics based tests of the pipe materials. Nowadays, several accelerated tests are available: PENT (Pennsylvania Edge Notch Tensile test), FNCT (Full Notch Creep Tensile test), CRB (Cracked Round Bar test) or SHT (Strain Hardening Test) and NCBT (Notched Cylindrical Bars Test). The PENT, CRB and SHT were applied to one unimodal polyethylene (PE 80), four bimodal polyethylene (three of PE 100 and one of PE 100‐RC) and one PE‐BF (for blow molding). The contribution is focused mainly on two topics: (i) difference in specimen's preparation and test conditions and (ii) comparison of the experimental results obtained using different accelerated tests.

Polyolefin thermoplastic elastomers from 1-octene copolymerization with 1-decene and cyclopentene

Thermoplastic elastomers (TPEs) are attractive materials because they combine the processing advantages and recycling potential of thermoplastics with the flexibility, low modulus, and soft touch of elastomers. In this article, the synthesis, characterization and mechanical properties of polyolefin TPEs are reported. A facile procedure is employed, through the chain-walking polymerization, to fabricate random copolymers of 1-octene with 1-decene and cyclopentene. The effect of the type and the feedstock comonomers concentration on the microstructure, the total branching and the branch-type distribution is studied. A comprehensive investigation on the mechanical behavior by uniaxial stretching until failure, step-cycle and creep tensile tests is carried out. All the copolymers behave as elastomers, with different mechanical properties strongly depending on the composition, structure and crystallinity.

Electrical resistivity and creep behavior of hypoeutectic Sn–0.5Cu based solders for flip chip technology

For flip-chip applications, there is a need to develop lead-free solders with low cost and suitable soldering characteristics, as a replacement for the traditional Sn–Pb solder. In this work, we investigate the effect of adding small amount of Zn and Bi elements into hypoeutectic Sn–0.5Cu Pb-free solders, which allows modification of their microstructure and improves their physical properties. Tensile creep testing was performed and a Garofalo hyperbolic-sine power-law relationship was created from experimental data to predict creep deformation mechanism as a function of stress and temperature. Results show that the favorable creep resistance of Sn–2.0Zn–0.5Cu solders was reduced considerably with Zn addition, having ten times higher creep rate at room temperature than Sn–0.5Cu. Of particular note is the observation of plastic energy dissipation ability of Zn-containing solder joints at room temperature. In contrast, with Bi addition, the number of fine Bi particles increased and the coarse Cu6Sn5 intermetallic compounds (IMCs) are emerged, which enhanced significantly the creep resistance and fracture time of Sn–2.0Bi–0.5Cu solder. The resistivity values of Sn–0.5Cu, Sn–2.0Zn–0.5Cu and Sn–2.0Bi–0.5Cu solders were on the order of 28–48% lower than that of Sn–40Pb solder (17.0 μΩ cm).

Correlation between structural changes of M23C6 carbide and mechanical behaviour of P91 steel after thermal aging

The results of thermal aging effect on the P91 steel after a long-term exposure at 600, 650 and 700°C are presented. Mechanical behaviour of the aged material was assessed by performing tensile, fracture toughness and short term creep tests along with microstructure examination. Sample aging duration and temperatures were chosen considering the structural changes of M23C6 carbide, which are described by the exponential equation as a function of time and temperature. The time-temperature dependence was previously established from M23C6 lattice expansion as a result of alloying elements’ diffusion into the carbide. The main focus is to determine whether the same relationship could be used for the assessment of the mechanical properties of P91 steel. Tensile, fracture toughness and creep test data at different aging duration and temperature indicated that predicted data correlate well with experimental data and gives a possibility to forecast changes caused by steel thermal exposure. Experimental results demonstrate that the used method provides a sufficiently good technique to predict the mechanical behaviour of P91 steel during aging.

Creep properties of simulated heat-affected zone of HR3C austenitic steel

Tensile creep tests on austenitic stainless HR3C steel pipe in an as-received state and after heat affected zone (HAZ) thermal cycle simulation by means of the GLEEBLE 3800 physical simulator were carried out at 923 and 1023K and an applied stress range between 100 and 350MPa to evaluate the effect of welding on its creep properties and behaviour. It was found that creep testing was conducted in a power-law creep regime. The results show a clear detrimental influence of the HAZ simulation on creep properties of HR3C steel at 923K and for very short creep exposure. However, with increasing time to fracture, the effect of weld simulation becomes less significant. By contrast, no such deterioration of creep properties was detected at 1023K. The evaluated similar values of the stress exponents of the minimum creep rate and the time to fracture are explained using the assumption that both creep deformation and the fracture process are controlled by the same mechanism. The main creep fracture mode was intergranular brittle fracture due to grain boundary creep damage.

Creep Behavior of Poly(lactic acid) Based Biocomposites.

Polymer composites containing natural fibers are receiving growing attention as possible alternatives for composites containing synthetic fibers. The use of biodegradable matrices obtained from renewable sources in replacement for synthetic ones is also increasing. However, only limited information is available about the creep behavior of the obtained composites. In this work, the tensile creep behavior of PLA based composites, containing flax and jute twill weave woven fabrics, produced through compression molding, was investigated. Tensile creep tests were performed at different temperatures (i.e., 40 and 60 °C). The results showed that the creep behavior of the composites is strongly influenced by the temperature and the woven fabrics used. As preliminary characterization, quasi-static tensile tests and dynamic mechanical tests were carried out on the composites. Furthermore, fabrics (both flax and jute) were tested as received by means of quasi-static tests and creep tests to evaluate the influence of fabrics mechanical behavior on the mechanical response of the resulting composites. The morphological analysis of the fracture surface of the tensile samples showed the better fiber-matrix adhesion between PLA and jute fabric.