Tensile Creep Research Articles

Effects of Ag on High-Temperature Creep Behaviors of Peak-Aged Al-5Cu-0.8Mg-0.15Zr-0.2Sc(-0.5Ag)

The tensile creep of Al-5Cu-0.8Mg-0.15Zr-0.2Sc(-0.5Ag) was tested at 150–250 °C and 125–350 MPa, and the effect of Ag on the high-temperature creep of Al-Cu-Mg alloys was discussed. After the addition of Ag, the high-temperature creep performances of the alloy were significantly improved at 150 °C/300 MPa and 200 °C/(150 MPa, 175 MPa). Then, constitutive relational models of the alloy during high-temperature creep were built, and the activation energy was calculated to be 136.65 and 104.06 KJ/mol. Based on the thermal deformation mechanism maps, the high-temperature creep mechanism of the alloy was predicted. After the addition of Ag, the creep mechanism of the alloy at 150 °C transitioned from lattice diffusion control to grain boundary diffusion control. At 250 °C, the mechanism was still controlled by grain boundary slip, but as the stress index increased and after Ag was added, the alloy fractures lead to the formation of dimples, thus improving the high-temperature creep performance.

Tensile and long-term creep properties of structurally and functionally integrated carbon fiber reinforced plastic at room temperature

Carbon fiber reinforced plastic (CFRP) based on phenolic resin have been widely used in aerospace and pressure vessel fields because of their high stiffness to weight ratio and excellent mechanical properties. In this paper, carbon fiber reinforced plastic were prepared by molding method using phenolic resin as the matrix. The fiber distribution inside the material and its influence on tensile fracture mechanism and creep properties were investigated. The specimens were prepared along horizontal and vertical directions. The test results show that the fibers tend to be distributed horizontally within the material and are influenced by the mold. Horizontal specimens with a large number of fibers parallel to the tensile direction exhibit more excellent tensile properties. The vertical specimen is loaded by the resin and interface with weaker properties inside. The fracture mechanism of horizontal specimens is fiber breakage, fiber pullout and resin fracture, while the fracture mechanism of vertical specimens is interfacial debonding and resin fracture. The difference in tensile fracture mechanism of horizontal and vertical specimens affects the creep properties of CFRP. The creep resistance of fiber is better than that of resin. Therefore, horizontal specimens exhibit better creep resistance in long-term creep tests due to the loads borne by the fibers. Modified Time Hardening model can accurately fit all experimental data. Creep curves can be predicted based on the model parameters.

Creep analysis of the flax fiber-reinforced polymer composites based on the time–temperature superposition principle

Abstract Natural plant fiber-reinforced polymer composites (PFRP) have emerged as an environmental-friendly material in the construction industry, but their creep behavior is a critical concern for load-bearing structures. This study investigates the creep behavior of flax fiber-reinforced polymer composites (FFRP) using the time–temperature superposition principle (TTSP). Due to the application of TTSP on the tensile creep behavior of FFRP is not fully understood, three potential methods for calculating the critical parameters during TTSP are compared to obtain an efficient application method to build the creep master curve. A 2,000-h long-term creep test is conducted parallelly on the same sample to validate the accuracy of the creep analysis results. The study proposes an ideal method to determine the key parameters in TTSP, providing valuable insights for the practical application of PFRP in the construction industry. Meanwhile, the research results in this study would be helpful in better understanding the creep behavior of FFRP via short-term accelerated tests.

Simple Estimation of Creep Properties of Negative Electrode for Lithium-Ion Battery

The macroscopic creep properties of negative electrodes in lithium-ion batteries and their estimation methods have been investigated based on the microscopic structure of the electrode. Tensile and creep tests were conducted on a negative electrode consisting of carbon powder and polyvinylidene fluoride (PVDF) binder. The stress-strain curve, the time history of the tensile strain, and the creep rupture time were measured in these tests and estimated using the simple model proposed in this study. The proposed model approximates the alignment of carbon particles as body-centered cubic (bcc) or face-centered cubic (fcc). The external load on the model was supported by a PVDF binder located between carbon particles. The test results showed that PVDF binder mechanical properties affect the macroscopic mechanical properties of the negative electrode, including the creep properties. The stress-strain curve and time history of the tensile strain were located between the upper and lower limits of the proposed model. The tensile strength and creep rupture time agree with the lower limit of the proposed model.

Early-Age Cracking Potential of Fly Ash High Performance Concrete Internally Cured with Super Absorbent Polymers

Abstract Early-age cracking is problematic for high performance concrete (HPC) made with a low water/binder ratio. The application of fly ash (FA) as a cement replacement can contribute to reduced CO2 emission and clinker factor, as well as improved durability of HPC. Super absorbent polymers (SAPs) were also applied for better curing and a higher rate of hydration to optimize the FA HPC. The current study utilized a temperature stress test machine to investigate the early-age cracking potential of FA HPC with internal curing by SAPs. Test results and the related analyses suggested that the introduction of internal curing alleviated the autogenous shrinkage, restrained stress, as well as tensile creep for HPC with 0 % and 20 % FA replacement level. The application of SAPs reduced the cracking potential of HPC with a low FA replacement level, whereas it aggravated the cracking when the FA replacement level was high.

Influence of recycled carbon fiber addition on the microstructure and creep response of extruded AZ91 magnesium alloy

In this study, the recycled short carbon fiber (CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion. The objective was to investigate the impact of CF content (2.5 and 5.0 wt.%) and fiber length (100 and 500 µm) on the microstructure, mechanical properties, and creep behavior of AZ91 alloy matrix. The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy. In comparison to the unreinforced AZ91 alloy, the composites with 2.5 wt.% CF exhibited an increase in hardness by 16–20% and yield strength by 5–15%, depending on the fiber length, while experiencing a reduction in ductility. When the reinforcement content was increased from 2.5 to 5.0 wt.%, strength values exhibited fluctuations and decline, accompanied by decreased ductility. These divergent outcomes were discussed in relation to fiber length, clustering tendency due to higher reinforcement content, and the presence of interfacial products with micro-cracks at the CF-matrix interface. Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy, suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep.

Effect of substituting Gd with 3 wt% Nd on high temperature creep behaviors of peak-aged Mg-10Gd-0.4Zr casting Mg alloy

In this paper, the high temperature creep behaviors of peak-aged Mg-10Gd-0.4Zr and Mg-7Gd-3Nd-0.4Zr casting alloys were investigated. The results showed that substituting Gd with 3 wt% Nd promoted precipitation of the β′ phase with higher number densities and larger aspect ratios, which led to the higher tensile mechanical properties of the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy at both room and elevated temperatures. The peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy had better tensile creep properties at temperatures of 200 °C–225 °C. However, the peak-aged Mg-10Gd-0.4Zr casting alloy showed better creep resistance when the creep temperature ≥250 °C. The creep mechanism for the peak-aged Mg-10Gd-0.4Zr casting alloy was dislocation climb assisted by grain boundary diffusion under all experimental conditions, while the creep mechanism of the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy transformed from dislocation glide at 200 °C–225 °C into dislocation cross-slip above 250 °C. Due to the faster transformation from β′ phase into β1 phase in peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy, the blocking effect of precipitation on dislocation movement was weakened. And a larger number of basal < a > dislocations accumulated in the grain boundary region, leading to precipitate free zones (PFZs) widening more obviously in the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy, and which well explained the reason why the creep resistance of peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy deteriorated rapidly above 250 °C.

Study on the microstructures and tensile creep behaviors of extruded dilute Mg–Mn–Zn alloys

In this work, creep behaviors of dilute Mg–Mn–Zn alloys were investigated in extruded rods (ER) with bimodal grain microstructures and extruded sheets (ES) with homogeneous microstructures. Tensile creep tests were carried out at 423 K along the extrusion direction (ED) and transverse direction (TD). For brevity, the samples were named as ER-ED, ER-TD, ES-ED and ES-TD, respectively. All samples' creep is dominated by dislocation movement, and different types of dislocation slip are seen in the different samples under loading along each direction. For the ER sample, the creep mechanisms of the ER-ED sample were determined to be cross-slip accompanied by pyramidal <c+a> slip. Differently, the creep of the ER-TD sample was dominated by basal slip and accompanied by grain boundary bulging, which induced the worst creep resistance. For the ES alloy, the creep mechanisms were pyramidal <c+a> and cross-slip, but the cross-slip density of the ES-ED sample was higher. Accordingly, the creep test results indicated that the creep resistance was ranked in an order of ES-TD/ED > ER-ED » ER-TD. Furthermore, bimodal grain microstructure accelerates creep at a similar texture effect level, where grain boundary bulging was clearly observed, as well as the decreased KAM and increased fraction of M/HABs (middle-to-high angle boundaries). These typical softening characteristics might be responsible for weakening the ER-ED sample from the highest room-temperature yield strength to the inferior creep resistance to ES-TD/ED samples, meaning the thermal instability of this strong heterogeneous microstructure.

Creep in Nanostructured Materials

The creep behaviour and properties of nanostructured materials are attributed to their operating deformation mechanisms, which could be different from those in their coarse-grained counterparts. Accordingly, in this review, recent progress on the creep behaviour of nanostructured materials will be described. The results of large sets of tensile creep tests on selected more complex metallic materials are analysed for evaluating the effect of different SPD processing methods on creep resistance at high temperatures. The resultant creep characteristics are compared with those attained in unprocessed conditions of the same materials. By contrast to the creep behaviour of UFG pure metals SPD processing of more complex materials mostly exhibits no essentially improved creep resistance. Evaluated stress dependences of the creep rate and the creep life suggest that creep deformation mechanisms in UFG materials are similar to those operating in coarse-grained materials. However, creep mechanisms in SPD processed materials are not clearly resolved and this is due to complexity of phenomenon and very small number of studies that have been carried out before now.

Effect of adding Indiana red matta rice husk Si3N4 bioceramic on mechanical, wear, flammability and tensile creep behavior of corn husk fiber polyester composite

AbstractThe objective of this study was to examine the effect of adding Indian red matta rice husk Si3N4 bioceramic on flammability, wear, mechanical and thermal behavior of corn husk fiber‐reinforced polyester composites. The Si3N4 bioceramic was prepared using thermo‐chemical process and subsequently surface‐treated using silane via aqueous solution method. The composites were made using hand layup method and post cured at elevated temperature. The results of this investigation suggest that adding 30 vol% of corn husk fiber improved the mechanical properties as compared to pure epoxy, however the Si3N4 addition outperformed. Similar to this, the composite with 4.0 vol% of bioceramic particle has the highest wear resistances, with a lowest sp. wear rate of 0.008 mm3/Nm and a coefficient of friction of 0.31. According to the flammability results, the composite contains 30 vol% of corn husk fiber and 4 vol% of Si3N4 (ECS3) has the lowered combustion rate of 6.72 mm/min. Finally, the composite ECS3 produced the lowest creep strain of 0.0104, 0.0122, 0.0149, 0.0241, and 0.0444 for 2000, 4000, 6000, 8000, and 10000 s respectively. These composites with improved properties could be used in cutting edge latest technologies as functional materials in automotive, defense, food packaging, structural, and domestic goods manufacturing.

Uncertainties in and recommendations to small punch tensile and creep tests for ductile materials

The objective of this paper is to clarify the complex nature which involves the interaction of several non-linear deformation mechanisms experienced in small punch tensile and small punch creep tests, and as a consequence, the associated difficulties in data interpretation. The paper starts with a highlight of some specific features experienced during small punch deformation, e.g., large deformation, high local plasticity, contact, the effect of initial plasticity, possible early cracking etc. and the consequences of them in data interpretation. Although several test standards have been available, uncertainties in data interpretation still exist and a universally accepted conversion method has not been available. On this basis, for the first time, critical comments on the uncertainties and applicability of the test methods in determining the tensile and creep properties and in high-temperature structural integrity assessment are addressed. Finally, recommendations on future developments are provided.

Microstructure and creep properties of cast hypereutectic Al-11Ce alloy with Si addition

This study systematically investigated the as-cast microstructure, heat and creep- resistance of Al-11Ce-xSi (x = 0, 0.9, 1.7 wt%) alloys. A tetragonal AlCeSi intermetallic compound was formed by adding Si. With the increase of Si content, the Chinese-script Al11Ce3/α-Al eutectics changed to rod-like structure and were gradually replaced by broad flaky AlCeSi/α-Al eutectics. The Al-11Ce alloy containing 0.9 wt% Si possessed the optimal tensile properties with an ultimate tensile strength of 129.2 MPa and an elongation of 4.3%, which were 8.4% and 65.4% higher than that of the based alloy, respectively. After aging at 400 ℃ for 1008 h, the microhardness of Si-containing alloys remained unchanged, indicating excellent coarsening resistance of the strengthening AlCeSi phases. Under tensile creep conditions at 300 ℃, the creep deformation of three alloys was the dislocation creep mechanism. Nevertheless, with the addition of 1.7 wt% Si, the steady-state strain rate of Al-11Ce alloy was decreased to 1/3 of its original value. The enhanced creep resistance was mainly attributed to the relatively high volume fraction of intermetallic phase, the reduced volume fraction of coarse primary phase, and the presence of AlCeSi precipitates that effectively hinder dislocations motion.

Use of the Iron Chloride Type of Lewis Acid Catalyst in High Reclaimed Asphalt Pavement Content Asphalt Mixtures

The use of reclaimed asphalt pavement (RAP) as a partial replacement for virgin aggregates and asphalt binders has received considerable attention recently. This approach is one of many promising methods for improving sustainability. However, many state Departments of Transportation are cautious in adopting high RAP content into their designs because of cracking and durability issues resulting from the aged RAP binder. A Lewis acid catalyst has been used to modify the asphalt binder’s chemical composition and disrupt the associated molecules formed in the aged RAP binder. The objective of this study is to assess the effectiveness of the use of a Lewis acid catalyst in improving the cracking resistance of an asphalt mixture containing high RAP contents. A suite of laboratory mechanical tests was performed, namely, the dynamic modulus test for linear viscoelastic properties; the semi-circular bend, Illinois flexible index, ideal cracking tolerance, and simplified viscoelastic continuum damage tests for fracture and fatigue resistance; the loaded wheel tracking test for rutting resistance and moisture susceptibility; indirect tensile creep compliance and strength tests for low-temperature cracking resistance; and the Cantabro abrasion test for durability. Further, AASHTOWare Pavement ME software was used to predict the long-term performance of asphalt pavements containing mixtures with high RAP contents and a Lewis acid catalyst. Results showed that the use of the Lewis acid catalyst can disrupt associated molecules formed in the aged RAP binder. Thus, asphalt mixtures containing high RAP contents (recycled binder ratio &gt; 0.20) and a Lewis acid catalyst exhibited similar performances to conventional mixtures. Further, Pavement ME predicted fatigue cracking was lower for a structure containing a FeCl3-modified mixture as compared to a similar one with no FeCl3, illustrating the effectiveness of FeCl3.

Effect of Water-to-Cement Ratios on Performance of Concrete with Prewetted Lightweight Aggregates

Lightweight aggregates (LWAs), as a popular material for internal curing (IC), have been extensively utilized in internally cured concrete (ICC). This paper investigated the development of mechanical properties, restrained shrinkage, quantitative stress relaxation, and tensile creep of ICC with prewetted LWAs under the condition of diverse w/c ratios (0.33, 0.40, and 0.50) by experimental investigations. Besides, the mixture proportion without IC was designed to investigate the effect of IC on the performance of the concrete mixture with a w/c ratio of 0.50. Corresponding results show that increasing the w/c ratio diminished the mechanical properties of ICC. A decrease in residual stress and stress rate was related to an increase in the w/c ratio. Relaxed stress and tensile creep increased with the w/c ratio increasing in ICC in the initial days. The introduction of IC decreased the mechanical properties, restrained shrinkage, stress rate, relaxed stress, and tensile creep of the concrete mixture with a w/c ratio of 0.50. The relationship between creep and relaxation coefficients was established, which contributed to the accurate evaluation of tensile stress development of ICC with prewetted LWAs under restrained conditions.

A Novel Smart CFRP Cable Based on Optical Electrical Co-Sensing for Full-Process Prestress Monitoring of Structures.

Carbon-fiber-reinforced polymer (CFRP) is a type of composite material with many superior performances, such as high tensile strength, light weight, corrosion resistance, good fatigue, and creep performance. As a result, CFRP cables have great potential to replace steel cables in prestressed concrete structures. However, the technology to monitor the stress state in real-time throughout the entire life cycle is very important in the application of CFRP cables. Therefore, an optical-electrical co-sensing CFRP cable (OECSCFRP cable) was designed and manufactured in this paper. Firstly, a brief description is outlined for the production technology of the CFRP-DOFS bar, CFRP-CCFPI bar, and CFRP cable anchorage technology. Subsequently, the sensing and mechanical properties of the OECS-CFRP cable were characterized by serious experiments. Finally, the OECS-CFRP cable was used for the prestress monitoring of an unbonded prestressed RC beam to verify the feasibility of the actual structure. The results show that the main static performance indexes of DOFS and CCFPI meet the requirements of civil engineering. In the loading test of the prestressed beam, the OECS-CFRP cable can effectively monitor the cable force and the midspan defection of the beam so as to obtain the stiffness degradation of the prestressed beam under different loads.

Creep properties and prediction model of composite solid propellant

In order to describe the creep properties of HTPB propellant, uniaxial tensile creep tests of propellant under different stresses were conducted. Based on the principle of viscoelastic theory, the Burgers model was used to describe the creep properties of the propellant. Combined with the experimental data, the parameters of Burgers model under different stresses were determined, and the model parameters were expressed as a function related to creep stress, and finally the model was verified by using the test data under creep stress 0.2 MPa. The results show that the Burgers model can describe the creep properties of the composite propellant well.

Superior tensile creep behavior of a novel oxide dispersion strengthened CrCoNi multi-principal element alloy

The creep behavior of an additively manufactured (AM) yttrium oxide dispersion strengthened (ODS) CrCoNi multi-principal element alloy (MPEA) is investigated in this study. Tests were conducted over a constant tensile stress range of 40–200 MPa and a temperature range of 973–1173 K. A stress exponent of 6.5 ± 0.1 and activation energies in the range of 335–367 kJ/mol were measured. Compared to its non-ODS counterpart and its parent alloy (CrMnFeCoNi), AM ODS CrCoNi has superior creep resistance at all tested stresses and temperatures. The mechanism contributing to the excellent creep resistance of AM ODS CrCoNi is attributed to the interaction of mixed character dislocations with oxide particles. The creep ductility of AM ODS CrCoNi is higher than its non-ODS counterpart due to a large percentage of low angle grain boundaries associated with its columnar grain structure. It was also found that creep ductility is significantly greater at the highest applied stress of 200 MPa compared to lower stresses. The steady state dislocation structure of AM ODS CrCoNi consists of long arrays of dislocations, which is different from that observed in non-ODS CrCoNi which consists of individual curved dislocations.

Effect of Carbon Nanotubes on the Mechanical, Thermal, and Electrical Properties of Tin-Based Lead-Free Solders: A Review

Carbon nanotubes (CNTs) are being applied with increasing frequency for advanced soldering. They have excellent mechanical, electrical, and thermal properties and are primarily used to reinforce lead-free solders. This paper discusses the strengthening mechanism of CNTs, introduces the preparation methods of CNT composite solders, and focuses on the review of tin-based lead-free solders reinforced with unmodified CNTs and metal-modified CNTs. The addition of CNTs can effectively improve the ultimate tensile strength, microhardness, shear strength, and creep resistance of the solder. However, the practical application of CNT composite solders has been a challenge for researchers for decades. The most significant issue is uniform dispersion due to the large density and surface differences between CNTs and solders. Other concerns are the structural integrity of CNTs and their limited addition amount, solder wettability, and interfacial bonding. CNT composite solders can only be widely used in a real sense when these challenges are properly addressed and overcome. At present, there is a lack of comprehensive reviews covering the structure, the strengthening mechanism, the preparation method of CNT composite solders, and the influence of CNT types on their strengthening effects. Therefore, this paper aims to fill this gap and contribute to solving the problems faced by the application of CNTs in solder. Future work is expected to focus on improving the dispersion and bonding of CNTs and optimizing the preparation method.

Effect of Na2CO3 on the tensile creep of slag-fly ash systems activated with Na2SiO3

The use of Na2CO3 in alkali-activated system (AAS) has attracted an increased interest since it provides a suitable setting time, suitable mechanical properties and lower cost. However, the tensile creep behavior of Na2CO3-activated AAS remains unknown, which is crucial for controlling its early cracking. Therefore, this study aims to investigate the effect of Na2CO3 on the tensile creep of slag-fly ash systems activated with Na2SiO3 (ASF). The total Na2O equivalent (Na2O of hybrid activators/binder, by mass) was maintained at 6%. Various Na2CO3 contents (i.e. the ratio of Na2O equivalent of Na2CO3 to total Na2O equivalent) were used in this paper, namely, 0, 1/3, 1/2 and 2/3. The compressive strength, flexural strength, elastic modulus, internal relative humidity, autogenous shrinkage, tensile creep and microstructures (X-ray diffraction, thermogravimetry, mercury intrusion porosimetry, scanning electronic microscopy-energy dispersive spectroscopy and nanoindentation) were investigated for the ASF system. Results indicate that the tensile creep of ASF mortar (ASFm) firstly increases and then decreases as the Na2CO3 contents increases. ASFm with Na2CO3 content of 1/2 has the highest tensile creep, which is 236.3% higher than that of ASFm without Na2CO3. When the Na2CO3 content increases from 0 to 1/2, Na2CO3 promots C(N)-A-S-H gel formation, increases the autogenous shrinkage and decreases the contact creep modulus of gels, leading to the increases of the tensile creep of ASFm. However, excessive Na2CO3 (content＞1/2) reacts preferentially with Ca ion dissolved from slag to generate CaCO3, inhibiting the gel formation. Moreover, CaCO3 plays a role in limiting the gel deformation, which remarkably reduces autogenous shrinkage and increases the contact creep modulus of gels, and therefore the tensile creep of ASFm is reduced.

Microstructure evolution and precipitation behavior in a Y2O3-bearing TiAl alloy during creep

The paper studies the microstructure stability of a Y2O3-bearing Ti–48Al–2Cr–2Nb alloy during creep. Tensile creep tests were performed at 800–850 °C under 100 or 275 MPa. Compared to thermal exposure, the low creep stress promotes the microstructure degeneration of lamellar colonies, mainly including α2-lath dissolution, γ-lath coarsening and βo phase precipitation. The high creep stress further accelerates the α2 → γ transformation, but goes against the precipitation of βo grains inside α2 laths. Similarly, more Cr-rich precipitates with the composition of Ti(Al, Cr)2 are observed in creep samples, which are identified as the C14-Laves phase. It has a {0001}C14//{111}γ and <101¯0>C14//<11¯0>γ orientation relationship with the γ phase. The high imposed stress also facilitates the precipitation behavior. It should be noted that there are a few C14-Laves phases precipitating along the Y2O3 interface by heterogeneous nucleation. The high strain energy around Y2O3 particles, especially under the high creep stress, contributes to the precipitation of C14-Laves phase not only at the Y2O3 interface, but also in the γ matrix.