Tensile Creep Tests Research Articles

Evaluation of the off‐axis and on‐axis tensile creep behavior of glass‐fiber reinforced polymer unidirectional lamina

AbstractThe off‐axis creep behavior of glass‐fiber reinforced polymer (GFRP) unidirectional lamina is crucial for engineering structural applications. A unified prediction model for time‐dependent off‐axis and on‐axis tensile creep strain in GFRP lamina is developed. The model, analogous in form to the one‐parameter plasticity model, accounts for off‐axis creep deformation separately for elastic and plastic response stages, incorporating a correction term to describe on‐axis creep deformation. The accuracy of the model is confirmed through tensile creep tests on unidirectional lamina at angles of 0, 15, 30, 45, 60, and 90 degrees. The model successfully predicts of creep deformation in the elastic and plastic response stages, respectively. The effects of creep stress, creep time, and off‐axis angle on the creep behavior are investigated. The optimal test angles for predicting off‐axis creep behavior using only two off‐axis angles' creep tests are analyzed. The dominant factors of creep behavior at various off‐axis angles are evaluated. The findings of the study include recommendations for lay‐up configuration and engineering applications of GFRP composites.Highlights A unified creep strain prediction model for GFRP lamina was developed. Creep strain was calculated separately in elastic and plastic response stages. The link between stress, time, angle and creep behavior was determined. The optimal test angles for predicting off‐axis creep behavior were evaluated.

High-Temperature Creep Resistance of FeAlOY ODS Ferritic Alloy.

A significant effort in optimizing the chemical composition and powder metallurgical processing led to preparing new-generation ferritic coarse-grained ODS alloys with a high nano-oxide content. The optimization was aimed at high-temperature creep and oxidation resistance at temperatures in the range of 1100-1300 °C. An FeAlOY alloy, with the chemical composition Fe-10Al-4Cr-4Y2O3 (wt. %), seems as the most promising one. The consolidation of the alloy is preferably conducted by hot rolling in several steps, followed by static recrystallization for 1 h at 1200 °C, which provides a stable coarse-grain microstructure with homogeneous dispersion of nano-oxides. This represents the most cost-effective way of production. Another method of consolidation tested was hot rotary swaging, which also gave promising results. The compression creep testing of the alloy at 1100, 1200, and 1300 °C shows excellent creep performance, which is confirmed by the tensile creep tests at 1100 °C as well. The potential in such a temperature range is the target for possible applications of the FeAlOY for the pull rods of high-temperature testing machines, gas turbine blades, or furnace fan vanes. The key effort now focuses on expanding the production from laboratory samples to larger industrial pieces.

Multiaxial creep deformation investigation of miniature cruciform specimen for type 304 stainless steel at 923 K using non-contact displacement-measuring method

Abstract Multiaxial creep investigations at high temperatures are required to guarantee the integrity of structural materials such as boiler pipes for power generation and turbine blades for aviation and industrial applications. The multiaxial creep testing method using a cruciform specimen has several advantages, and the authors successfully downsized the specimen. The authors also developed a technique for the in situ observation of the specimen in an electric furnace and the non-contact displacement measurement in the development of a biaxial tensile creep testing machine for the miniature cruciform specimen. By observing the specimen at a target mark during the creep testing through an observation window installed at the bottom of the furnace, it was possible to visualize the specimen surface variations and obtain the axial strain from the locus of the target marks. The Mises-type equivalent strain was calculated from the axial strains obtained in the equi-biaxial tensile multiaxial creep testing and was compared with the strains obtained in the uniaxial creep testing. The Mises-type equivalent strain can be expressed using a unified method up to approximately 5% of the initial strain in the test, even in the multiaxial stress state.

High temperature tensile creep behavior and microstructure evolution of Ti60 alloy rolled sheet

In this work, the high temperature tensile creep test of 2mm Ti60 alloy rolled sheet was carried out, and the creep behavior and microstructure evolution were studied. The initial microstructure of the 2mm Ti60 alloy rolled sheet is mainly composed of primary α phase and secondary α phase, and there are many dislocations and dynamic recrystallization (DRX) inside the rolled sheet. According to Norton-Bailey law, the creep stress exponent at 600 °C is calculated to be 3.6, and creep activation energy at 200MPa is calculated to be 286.4kJ/mol. It implies that the creep mechanism of the rolled sheet includes dislocation slip and dislocation climb. The initial Ti60 alloy rolled sheet has the {0001}<10-10>α texture. Stretching along the RD makes the texture direction gradually change from B-type (<0001>//ND) to T-type (<0001>//TD). Whether it is the B-type texture or T-type texture, the (0001) plane of the α phase always exhibits a basal texture state parallel to the tensile stress direction, contributing a good tensile creep property of this alloy sheet.

Improved creep resistance of short carbon fiber reinforced polyetherimide composite by solution mixing method

Creep resistance is critical for ensuring the dimensional stability and safe operation of composite components. However, the creep resistance of short fiber reinforced thermoplastic composites has been rarely reported and that of the composites manufactured by conventional extrusion compounding combined with injection molding is kind of low. In this work, in order to address this issue, two short carbon fiber-reinforced polyetherimide (SCF/PEI) composites named respectively as SCF/PEIE and SCF/PEIS are prepared by both conventional extrusion compounding and our newly developed solution mixing method combined with injection molding. The solution mixing method involves the dispersion and mixing of carbon fibers within a PEI solution and allows for the retention of longer fiber lengths. Experimentally, the creep behaviors of the SCF/PEI composites were examined through tensile and flexural creep testing at various stress levels in a wide temperature range. Theoretically, the creep behaviors were characterized by employing the Schapery model and the time–temperature superposition principle (TTSP), and the impact of fiber length retention on creep resistance was quantitatively analyzed using the Fu-Lauke model. The results demonstrate that compared to the SCF/PEIE composite, the SCF/PEIS composite exhibits a higher creep fracture stress level (175 MPa) and a more extensive linear viscoelastic region (0–85 MPa) at room temperature. Furthermore, the SCF/PEIS composite was observed to have a significantly longer secondary creep stage at an elevated temperature of 210 °C. Overall, the creep resistance of the newly manufactured SCF/PEIS is significantly superior to that of the SCF/PEIE, which effectively extends the service life and operational capacity of injection-molded SCF/PEI composites.

Grey correlation analysis of asphalt-aggregate adhesion with high and low-temperature performance of asphalt mixtures

The adhesion work and force of the five types of asphalt to andesite were measured using surface energy and pull-out tests, respectively. Various tests were operated to estimate the high and low-temperature characteristics of the five types of asphalt mixtures: high-temperature rutting, low-temperature bending, indirect tensile creep, and thermal stress restrained specimen tests. Furthermore, the high and low-temperature evaluation index, adhesion work, and adhesion force of these asphalt mixtures were analyzed using grey correlation analysis. The results show that compared with the adhesion work, the actual contact between mineral aggregate and asphalt in the pull-out test leads to the difference in adhesion force and work measured by SBS-modified, SBR-modified, and extreme cold asphalt. The correlation degree of adhesion work and force to the evaluation indexes of high and low-temperature properties in asphalt mixture is roughly the same, and the adhesion work has a more momentous impact on the high and low-temperature properties in asphalt mixtures. The adhesion work and force correlate best with low-temperature bending test parameters and thermal stress restrained specimen test (TSRST) parameters related to fracture failure of asphalt mixture, followed by the indirect tensile creep test parameters. It shows that the adhesion work and force significantly impact the low-temperature characteristics of asphalt mixture more than their high-temperature stability.

Creep properties of heat-resistant ultrafine-grained Al (HITEMAL©) determined by small punch testing

The creep properties of thermally stable ultrafine-grained Al metal matrix composite strengthened and stabilized by continuous in situ amorphous Al2O3 network (named HITEMAL©) prepared by powder metallurgy (PM) were tested by small punch creep testing (SPCT) in the temperature range from 573 to 673 K. The experimental SPCT results were correlated and compared with the results obtained by conventional tensile creep testing. The mutual correlation between tensile and SPCT creep results based on the transition stress was proposed and used to correctly interpret the measured SPCT data. The creep behaviour of HITEMAL© is characterized by the high values of apparent stress exponents and by the presence of transition stress at which the apparent stress exponents significantly changed. The SPCT discs fractured by the radial cracks at low values of deflection with only limited creep deformation highly localized in the vicinity of the fracture surfaces. The detailed analysis of fractured SPCT discs by scanning electron microscopy showed ductile dimpled fracture surfaces with the presence of unusual high filament-like tearing edges. The comparison of obtained results with other PM Al-based alloys and composites confirmed a significantly higher creep performance of HITEMAL© at used testing conditions.

Room-Temperature Creep Deformation of a Pressure-Resistant Cylindrical Structure Made of Dissimilar Titanium Alloys

The long-term safety of pressure-resistant structures used in deep-sea equipment may be threatened by creep deformation. The creep deformation behavior of a pressure-resistant structure made of different titanium alloys, Ti-6Al-4V and Ti-4Al-2V, at room temperature is investigated in this research. The kinetics and mechanisms underlying creep deformation in these materials is explained by proposing an improved constitutive model considering the effects of stress level, loading rate and environmental temperature field, offering crucial information for optimizing design parameters and guaranteeing the lifespan of the structure. Model parameters are determined for the two types of titanium alloys based on tensile creep testing results and validated through a simulation of the experimental process. In this study, a material creep model was used to predict the long-term deformation of large pressure-resistant titanium structures to ensure safe long-term operation. The safety factor used in the model is 1.5. Finite element analyses are conducted for the creep behavior of the pressure-resistant structure under real operating circumstances based on the creep constitutive model. The simulation predicts stress distribution, strain evolution, and deformation size over long periods of time by integrating complicated geometries, boundary conditions, and material characteristics. The present research can provide basic information for the local impacts of creep deformation on the inside of facilities, which helps refine design strategies to reduce possible damage risks.

Effect of Ni-RGO nanosheets on the creep behavior of Sn–Ag–Cu composite solder joints

Creep damage of Sn–Ag–Cu micro-joints is inevitable in service, even at room temperature. In this study, Ni-decorated reduced graphene oxide (Ni-RGO) nanosheets were rationally selected as a promising reinforcement in Sn-3.0Ag-0.5Cu (SAC305) solder to improve creep resistance. Tensile creep tests were conducted on the Ni-RGO reinforced SAC305 micro-joints under 8–14 MPa stress at 100–150 °C by dynamic mechanical analysis (DMA) equipment. Micrography and fractography were observed using FESEM. The stress exponent (n) increased from 5.83 to 6.37, and the activation energy (Q) rose from 68.80 to 75.41 kJ/mol as 0.10 wt% Ni-RGO nanosheets were added into the SAC305 solder, indicating the occurrence of diffusion mechanism. By adding a trace amount of Ni-RGO nanosheets (no more than 0.10 wt%), the crack initiation was prone to occur at the wave-valley of the continuous scallop shaped interface, where the diffusion of vacancies occurred, resulting in hybrid-fracture features of quasi-cleavage and dimples. It can be concluded that the inclusion of trace amounts of Ni-RGO nanosheets can enhance the creep resistance of SAC305 micro-joints during service.

Development of lightweight structural concrete with artificial aggregate manufactured from local clay and solid waste materials

The partial replacement of conventional natural coarse aggregate (NCA) with artificial light weight aggregate (LWA) manufactured from local clay and solid waste to develop a lightweight aggregate concrete (LWAC) for the structural use was studied in this paper. Red clay and Savar clay were used individually with solid wastes like rice husk ash (RHA) and waste glass to produce LWA. The suitability of raw materials and LWA was evaluated by investigating various properties. The mechanical, thermal and durability properties of manufactured LWAC were explored. The results of physical, chemical, thermal and geotechnical properties revealed that Red clay is better than Savar clay for the preparation of LWA. All the physical and mechanical properties of LWA prepared from Red clay are suitable for the preparation of LWAC compared to Savar clay. The test results demonstrated that the concrete manufactured by replacing 30 % of NCA with LWA produced a concrete of lightweight properties. The compressive strength of LWAC for 7 and 28 days was observed as 28 and 48 MPa, respectively. The results of modulus of elasticity, splitting tensile strength, flexural deformation, and creep test of LWAC revealed that these mechanical properties meet the requirements for the structural concrete. The RCP test proves that chlorine permeability of LWAC is comparable with NCA. It was observed that the superior performance of LWAC can be achieved only when the optimized mix designed is followed strictly. The suitability of the replacement of natural aggregate by LWA may be helpful for Bangladesh due to the scarcity of natural coarse aggregate and reusability of solid waste materials.

A novel under-aging design to improve the creep rupture life of a precipitation-strengthened Fe–Ni-based superalloy

The under-aging, peak-aging, and over-aging microstructures of a precipitation-strengthened Fe–Ni-based alloy were designed by applying different heat treatment procedures. Tensile creep tests were conducted at 700 °C and 250 MPa on samples exhibiting different strengthening γ′ precipitate volume fractions and diameters. The creep life of the alloy in the under-aged state was increased by more than 10% compared to the peak-aged condition, which provided a new approach to designing the heat treatment regime that improve the creep rupture life and plasticity of precipitation-strengthened alloys. The improvement in creep properties of the under-aged state was attributed to the transition from shearing to Orowan looping of γ′ particles by matrix dislocations during the dynamic precipitation and coarsening of γ′ phase, increasing intragranular deformation resistance. The under-aged microstructure design allowed reducing the grain boundary sliding contribution to overall strain during creep. As a result, the steady-state creep stage of the alloy in the under-aged state was extended. Additionally, relationships between applied stress and nucleation, growth, and coarsening of the γ′ phase have been evidenced.

Role of Austenite Stability in Elevated Temperature Mechanical Properties of Gas Metal Arc-Directed Energy Deposition Austenitic Stainless Steels

A gas metal-directed energy deposition process was used to fabricate builds using two commercial weld fillers used in power generation applications, 16-8-2 and 316H. Microstructure stability and mechanical properties were investigated through room-temperature and elevated temperature tensile testing and creep testing at 650°C, 750°C, and 825°C. 16-8-2 exhibited reduced austenite stability which resulted in athermal martensite formation after aging at 650°C for 1000 h and strain-induced martensite formation during room-temperature tensile testing. 316H exhibited relatively higher austenite stability due to increased alloying content, resulting in no athermal martensite or strain-induced martensite. Due to lower austenite stability, ferrite formed during creep at 650°C in 16-8-2, which resulted in reduced creep life and lower creep ductility compared to 316H. At 750°C and 825°C, when ferrite is no longer thermodynamically stable, 16-8-2 exhibited longer creep life and similar creep ductility as 316H. The formation of ferrite in 16-8-2 appears to have a greater impact on creep performance than the formation of embrittling topologically close-packed phases like the σ phase, as 316H exhibited superior creep performance while predicted to form 14 vol.% σ phase at 650°C.

Effect of Individual Alloying Addition on the Microstructure and Creep Behavior of Squeeze Cast AZ91 Magnesium Alloy

The microstructure of AZ91 (Mg-Al) alloy is comprised of α-Mg and β-Mg17Al12 massive phase. The lower melting point associated with the β-Mg17Al12 phase results in poor creep resistance of the alloy. In the present study, the AZ91 alloy with the addition of calcium (Ca, 1wt%) and cerium (Ce, 1wt%) is cast, and their effect on the microstructure and creep behavior of AZ91 alloy have been investigated. Thermally stable phases such as Al2Ca and Al11Ce3 are introduced in the AZ91 alloy through the addition of Ca and Ce elements. Energy dispersive spectroscopy (EDS) and x-ray diffraction analysis confirmed the presence of these intermetallic phases in the microstructure. Tensile creep tests on the as-cast samples were performed at 175°C temperature under 50 MPa stress. The study shows that the creep resistance of AZ91 alloy is greatly improved with the presence of Al2Ca and Al11Ce3 intermetallic phases because of their better thermal stability than β-Mg17Al12.

Laboratory Evaluation of Tensile Creep Behavior of Concrete at Early Ages

Short-term uniaxial tensile creep tests were conducted for early-age concrete at different ages in an effort to characterize early-age concrete as an aging viscoelastic material. Based on the test results, the viscoelastic material properties of the test concrete were characterized in terms of the Dirichlet series creep compliance and relaxation modulus functions. Applications of the model to the numerical analysis of the test samples showed a good agreement between the tests and computational results for the samples tested at different ages. This paper presents the test procedures and data analysis with a brief introduction of theoretical background.

An Interpretation between Small Punch Creep and Uniaxial Tensile Creep Test: Computational and Empirical Approach

The relationship between Small Punch (SP) creep testing and uniaxial tensile creep testing is crucial for translating findings from the innovative SP methodology to more conventional testing paradigms. This study involves both computational and empirical approaches to correlate the two testing methods effectively. The computational approach primarily utilizes finite element analysis (FEA) to model and simulate the stress states and deformation behaviors in SP creep tests. The empirical approach involves developing empirical relationships based on experimental data from both SP and uniaxial tensile creep tests. By integrating computational and empirical approaches, researchers can achieve a robust and reliable interpretation of SP creep test data in terms of conventional tensile creep test results.

Creep behaviors of Mg–6Zn-0.4Mn-0.3Al-0.2Ca (wt.%) alloy enhanced by icosahedral quasicrystal

Magnesium (Mg) alloys are considered to be the lightest metal structural materials, however, their poor creep resistance considerably limits their applications. In this study, a novel Mg–6Zn-0.4Mn-0.3Al-0.2Ca (ZMAX6000) alloy with icosahedral quasicrystal phases (I-phases) distributed at almost all triangular grain boundaries was developed by hot extrusion and heat treatment. Tensile creep tests were systematically conducted on the alloy at temperatures of 398 K, 423 K, and 448 K under stresses of 50 MPa, 70 MPa, and 90 MPa, respectively. These I-phases could reduce the accumulation of creep damage at triangular grain boundaries, hinder grain boundary sliding, and delay the generation of cracks. As a result, the ZMAX6000 alloy exhibited far superior creep properties compared to ZK60 and AZ91 alloys. During the creep process, non-basal slip occurred and the texture intensity of the sample was weakened. Dislocation characterization results showed that the creep mechanisms of the alloy at 448 K under 90 MPa were cross-slip and pyramidal < c + a > slip.

Continuum Mechanics Models for Describing the Creep and Physical Aging Behaviors of Laminated Composites

Two types of carbon fiber-reinforced epoxy composite laminates are chosen for long-term tensile creep tests under different temperatures and load levels. Their time-dependent and non-monotonic deformations indicate clearly both temperature effect and physical aging effect. To characterize these viscoelastic behavior, two phenomenological constitutive models and one physical model are developed. The linear viscoelastic model based on the Boltzmann superposition principle is able to describe reasonably the deformations at relatively lower stress levels and temperatures. The nonlinear viscoelastic model of Schapery’s single-integral form, together with a usage of effective time theory, could describe nicely all the effects of temperature, stress, and physical aging. The physical model based on Ngai’s coupling mechanism concept is further combined with the framework of Schapery’s nonlinear viscoelastic theory, which may provide certain physical understanding about the effect of aging behavior on long-term creep deformation of the laminated composites. Numerical modelling by finite element method are implemented, and comparisons between the experimental and simulation results are demonstrated.

Long‐term creep deformation of carbon fiber/epoxy composites with physical aging: Experimental investigation and constitutive modeling

AbstractThe tensile creep tests for two kinds of epoxy resin matrix composite laminates were performed under 25°C and 50°C. Results indicate that these materials deform in a time‐dependent manner, that is, the tensile strain increases within a short time after the tests began, and then decreases during most of the loading period. Such increase and decrease trends reflect the creep characteristic and effect of physical aging, respectively. A linear viscoelastic model is developed to include both the creep temperature effect and physical aging effect, starting from the Boltzmann superposition principle. In modeling, these two effects both contribute to the transient compliance and result in the increase and decrease of the transient compliance. Time–temperature/aging time superposition principle is adopted to deal with the influences of temperature and physical aging. This theoretical model is further implemented numerically within a finite element framework. To verify the newly proposed model, not only the experimental and numerical results of the tensile deformations of laminates are compared, but also the bending deformations of structural components made from the above laminates are analyzed.Highlights Tensile creep tests were done for carbon fiber/epoxy laminates. The strain shows creep temperature and aging effect (TE and AE). New constitutive relation was proposed to describe the TE‐ and AE‐caused strains. Structural‐level flexure creep tests and simulation analyses were conducted.

Linear and nonlinear tensile creep of steam-cured UHPC

In bridges, UHPC can bear significant sustained tensile stress without cracking under service loading. Its significant impact on the long-term behavior of large-span bridges due to tensile creep characteristics becomes evident. In this paper, both linear and nonlinear tensile creep behavior of steam-cured UHPC was experimentally investigated by using dog-bone-shaped specimens under sustained direct tension for a duration of 360 days. The tensile creep test was conducted under varied tensile stress levels ranging from 0.3ft to 0.9ft. Tensile creep coefficients were calculated by using the experimental results. Nonlinear tensile creep occurs in the steam-cured UHPC when the sustained tensile stress is larger than 0.3ft. The threshold of nonlinear tensile creep is lower than that of normal-strength concrete under compression. When the sustained tensile stress is larger than 0.8ft, tensile creep failure occurs a short time after loading. The nonlinear creep impact under tension is less pronounced than that under compression due to the distinct function of steel fibers within UHPC when subjected to compression and tension force. The findings in the scanning electron microscopy (SEM) test reveal that the mechanism driving the nonlinear tensile creep of UHPC is the damage growth at the fibers-matrix interface under the high sustained tensile stress. A design-oriented model for the creep coefficient of UHPC is developed, which incorporates both linear and nonlinear creep effects. The model’s credibility is verified using the experimental results.

Creep crack tip opening displacement (CCTOD) of X80 pipeline steel at room temperature

The room temperature creep behavior of X80 pipeline steel has attracted increasing attention because it is considered to be the main cause of time-delayed failure in pipeline steel. The crack tip opening displacement (CTOD) is a general criterion to characterize the time-delayed failure and assessment safety of pipeline steel. However, there are few methods to demonstrate crack behavior of the pipeline steel caused by room temperature creep. Based on the traditional CTOD theoretical model, a modified creep crack tip opening displacement (CCTOD) theoretical model is presented to calculate the CCTOD from the crack mouth opening displacement (CMOD). The room temperature creep experiment with a single edge notched beam subjected to three-point bending creep load for 36 h at room temperature is performed to know more about the CCTOD of X80 pipeline steel. Based on a power-law time delayed relationship among creep strain, stress and time fitted from experiment results of tensile creep tests, the finite element model is also established to evaluation the CCTOD of pipeline steel at room temperature. It is found that there is about 10% CTOD increment caused by room temperature creep added to that of the traditional elastic and plastic CTOD which indicates that room temperature creep is also further blunted the crack tip of X80 pipeline steel. Meanwhile, The results will provide an approach for failure evaluation and an integrity guideline for X80 pipeline steel.