Constant Tensile Load Research Articles

Effect of pre-strain on hydrogen-induced delayed cracking and hydrogen trapping behavior in high-strength martensitic steels

Pre-strain is a key factor affecting the critical conditions for hydrogen-induced delayed cracking (HIDC). In this study, the threshold stress and critical hydrogen concentration for HIDC of MS1300 and MS1500 steels with different pre-strains were measured by constant load tensile (CLT) tests. The results demonstrated that although MS1500 has higher strength, its safe service strength is lower than that of MS1300 when the hydrogen content exceeds 0.5 wppm. Additionally, the hydrogen penetration, thermal desorption spectroscopy, and hydrogen microprinting methods were also used to analyze the hydrogen-induced failure mechanism. These studies provide an effective data reference for improving the industrial production process.

Factors affecting the tensile strength of bituminous geomembrane seams

The tensile shear strength, break location, and constant tensile load failure times are examined for seams made from one 4 mm-thick bituminous geomembrane (BGM) product, with corresponding observations specific to that material. In short-term tests, failure is observed within the sheet material once the seam strength exceeded 0.8 times that of the sheet material. The effects of seam thickness reduction and overlap width on seam strength are examined for two methods of seaming. Seams with a short-term strength meeting or exceeding 80% of the sheet strength are subjected to constant tensile loads between 18 and 55% of sheet ultimate strength and the time to failure is reported. The relationship between short-term seam strength and time to failure under sustained load and thickness reduction and squeeze-out is investigated. Constant tensile load testing is proposed as a construction quality assurance procedure to assess the degree of geotextile engagement of field seams.

Experiments on Low–Cycle Ductile Damage and Failure Under Biaxial Loading Conditions

BackgroundThe damage and failure behavior of ductile metals depends on the stress state as well as on the loading history. Biaxial experiments with suitable specimens can be used to targeted generate different loading conditions, thus allowing the investigation of a wide variety of load cycles with different stress states.ObjectiveIn the biaxial experiments with the newly presented HC-specimen cyclic shear loads are superimposed by various constant compressive and tensile loads. Buckling during compressive loading in both axes is avoided by an additional newly introduced downholder.MethodsThe strain fields at the surfaces of the biaxial specimens are evaluated by digital image correlation (DIC), and after failure the corresponding fracture surfaces are analyzed by scanning electron microscopy (SEM). Associated numerical simulations employing the presented material model provide information on the current stress states.ResultsThe introduced downholder successfully prevents buckling during compressive loading. The strain fields detect a clear influence of the shear direction and a tensile superposition of the cyclic shear load leads to more brittle and a compressive superposition to more ductile behavior. The accompanying numerical calculations reveal the associated, different stress states.ConclusionsThe new experimental program with biaxially loaded specimens for the investigation of damage and failure behavior under cyclic loading enables the targeted examination of a wide variety of load cycles and is thus suitable for the comprehensive analysis of these phenomena.

In situ monitoring of stress corrosion at the Alloy 625|NaCl interface

Digital holography was used for in situ monitoring of the dynamic stress corrosion processes occurring at the Alloy 625|0.5 M NaCl interface. The introduction of elastic deformation to Alloy 625 through constant extension rate tensile loading increased the anodic and corrosion currents. These increases were attributed to the increased stress caused by elastic deformation, which increased the number of defects in the oxide film on the surface of Alloy 625 and promoted stress corrosion; this was verified by the fact that the accept density (NA) was nearly ten times greater with elastic deformation than without elastic deformation. Intergranular corrosion (IGC) was induced without elastic deformation. IGC induction occurred because chloride ions were readily adsorbed at the grain boundaries and were more active than the grain bodies. However, the application of elastic deformation induced cracks on the alloy surface to enhance stress corrosion, and it inhibited the development of IGC because the cracks were more susceptible to corrosion than the grain boundaries. In-line digital holography revealed that the cracks were initiated in a certain area and progressively advanced to adjacent areas with applied elastic tensile stress.

Effect of pre-strain on critical conditions for hydrogen-induced delayed cracking and crack nucleation characteristic of DP1180 steel

Hydrogen-induced delayed cracking represents a significant threat to the dependable performance of advanced high-strength steel. This study employed constant load tensile tests to uncover critical conditions for hydrogen-induced delayed cracking of DP1180 steel plate, establishing a precise relationship between pre-strain, threshold stress, and critical hydrogen concentration. Furthermore, this research explored dislocation slip transfer at grain boundaries, utilizing geometric compatibility factor (m') and residual Burgers vector (br), and analyzed slip characteristics at martensite/martensite, ferrite/ferrite, and martensite/ferrite interfaces. These findings provide valuable references for the safety assessment of DP1180 in hydrogen-exposed environments.

Durability assessment of GFRP bars exposed to combined accelerated aging in alkaline solution and a constant load

Employing fiber-reinforced polymer (FRP) bars as reinforcement in reinforced concrete (RC) elements is a promising approach to solve the issues associated with steel corrosion in RC elements owing to the high corrosion resistance of FRP bars. Although a number of studies on the durability of glass FRP (GFRP) bars in the alkaline environment are available, most of which ignored the influence of sustained loads. This paper presents an experimental program on tensile tests on GFRP bars made of three distinct matrix resins (i.e. epoxy, vinyl ester and polyester), after exposure to combined alkaline solution immersion, an elevated temperature and a constant load. A novel level device was developed, and a prescriptive constant axial stress was imposed on GFRP bars, and the bars with or without a sustained load were exposed to an alkaline solution and an elevated temperature of 60 °C. The main parameters investigated in the present study included aging times, constant stress levels, exposure conditions and types of resin matrices of the GFRP bars. The residual tensile properties of the GFRP bars were tested and presented. The microscopy method was adopted to check the internal defects in the GFRP bars with or without exposures. Test results show that three months of exposure in alkali and loading could lead to more than 40% strength decreases of the GFRP bars. Compared with GFRP bars after exposure to alkaline solution solely, the presence of the constant tensile load only leads to small further detrimental effect in tensile properties of GFRP bars.

Creep behavior of 3D printed polymer composites

AbstractThe creep behavior of polymer composites containing different weight percentages of poly(lactic) acid (PLA), thermoplastic polyurethane (TPU), and poly(ethylene) glycol (PEG) is experimentally characterized and computationally modeled using finite element analysis (FEA). The composite filaments are manufactured with melt extrusion method by using twin‐screw extruders, and then are employed in the 3D printing of creep samples. The samples are tested under a constant tensile load of 100 N. In this study, the computational model is developed by using the Generalized Voigt‐Kelvin solid model and three terms in Prony series. The equations of Prony series were obtained by the Laplace transformation of Kelvin model. The experimental creep displacements and strains are compared with computational results, and a good agreement between them is observed. The maximum error percentage in computational result is approximately 6% as compared to the experimental result. Hence, it can be said that the relatively simple computational models developed are reliable and can be used to study the creep behavior of similar polymers. The error percentages can still be reduced by considering a higher number of terms of Prony series in the model.Highlights Studied creep behavior for additively manufactured thermoplastic polymer composites. Developed computational model using three terms of relaxation modulus. The experimental results correlate very well with the computational model. Computational models can be used for other polymers.

Experimental study on high temperature tensile behaviour of aluminium alloy AA5083 with oscillating load

The flow behaviour of aluminium alloy AA5083 at 450 ^circ C has been investigated under quasi-static loading conditions with and without a superimposed oscillating load. Samples were placed under tensile load at constant strain rates ranging from 0.001 to 0.3 s^{-1}. A fixture was designed to generate the required sine-wave oscillation and was attached to the MTS tensile test machine along with a secondary, highly sensitive load cell. The frequencies of the imposed oscillations ranged from 5 to 100 Hz with an amplitude ranging from 0.02 to 0.5-N. It was observed that the imposition of oscillations influences the deformation behaviour of the material. Although the yield and tensile strength remain relatively constant, the total elongation is 8–23% higher under an imposed oscillating load. In addition, the thickness distribution profiles along the gauge length of the tensile specimens were investigated and it was observed that in the presence of oscillations the thickness distribution is more uniform. It was concluded that the presence of a superimposed oscillative load will result in greater deformation capabilities before fracture and postpone the occurrence of damage compared to conventional forming. This phenomenon was further explored utilising a user-defined material subroutine developed for the finite element solver LS-DYNA to simulate the conducted constant load tensile tests.

EFFECT OF STAINLESS STEEL 304 TIG WELDING AMPERE ON STRESS CORROSION CRACKING PHENOMENON

This article discusses the experimental results of stress corrosion cracking grade 304 stainless steel after GTAW welding under environmental corrosion simulation. The corrosion phenomenon that occurs is Stress Corrosion Cracking (SCC). The experimental method is a specimen welded using a current of 55, 60, and 65 Ampere respectively with a gas flow rate of 5 L/min argon shielding gas. The constant tensile loads of 2000 N and 4000 N in the state of the test object immersed for 2 x 24 hours in a solution of HCl + Aquades. Different Ampere and shielding gas flow rate parameters affected the cracks phenomenon. Vickers Hardness and Microstructure were used to evaluate the weld area. The lowest ampere of the weld results in maximum rough cracks from the surface and it's visible on the surface. The increased hardness of the 55 Ampere current specimen indicates a change in structure or phase after welding. The highest ampere produces fine cracks on all surfaces.

Steel-concrete bond behaviour of concrete mixes with wood waste: pull-out and bending tests of full-scale beams and columns

The present work intends to encourage a more widespread application of concrete mixes containing wood waste by investigating the steel–concrete bond of ordinary steel reinforcement bars and prestressed strands to assess the feasibility of using these composites in structural applications.After a set of preliminary tests, two mixes were selected in which aggregate was partially replaced by wood chip and sawdust. The effect of the steel–concrete bond length and reinforcement diameter on the shear strength was evaluated for steel bars and two-wire strands.The incorporation of wood appears to create a better mechanical interaction by increasing the component of friction as a resistance mechanism. In the case of the strands, the bond resistance is significantly higher (above 2.3 MPa) than the reference (0.9 MPa), regardless of the wood-concrete composites and the bond length. Additional tests have been performed to evaluate a possible creep effect. The specimens were subjected for 120 h to a constant tensile load corresponding to 50% of the mean results of the pull-out test. Results show that incorporating wood does not enhance the creep for this load level.Full-scale structural elements were also constructed to assess the feasibility of using these composites in structural applications. Bending and bending plus fatigue tests were performed to determine the behaviour under static and dynamic loads. It was concluded that the reference concrete without wood incorporation cracked for lower loads (26.0 kN) than the composites with wood (above 38.8 kN) and presented much higher bending stiffness (27835 kN.m2) than the wood-concrete composites (below 8544 kN.m2). The wood concrete with sawdust resisted fatigue tests without cracking.

Equivalence in evaluating hydrogen-assisted fracture strength of slow strain rate tensile and constant load tensile for three precipitation-hardened martensitic stainless steels: Effect of large-sized particles

This study investigated the equivalence in evaluating hydrogen-assisted fracture strength undergoing slow strain rate tensile (SSRT) and constant load tensile (CLT) for three precipitation-hardened martensitic stainless steels containing second-phase particles of different sizes. For both PH13–8Mo and 17–4PH with nano-sized precipitates, the fracture strength was higher for SSRT than for CLT. However, for 15–6PH with both nano-sized precipitates and large-sized carbides, cracks at the larger-sized carbide/matrix interface led to the lower fracture strength for SSRT. Furthermore, we concluded that the hydrogen-assisted threshold fracture strength of CLT could be estimated by using SSRT if no large-sized particles were in high-strength steels.

A mixed stress-strain driven computational homogenization of spiral strands

Spiral strands subjected to tensile force and bending loading display a nonlinear dissipative behavior due to frictional interactions between their elementary wires. This study aims to provide an efficient method, based on a computational homogenization procedure, to accurately characterize the nonlinear response of such strands. By using 1D beam elements in both micro- and macro-scale, homogenization is performed along the axial direction of a representative volume element (RVE), leading to expressing a boundary value problem on RVE, driven in a mixed manner by either strains or resulting forces or moments. The boundary value problem on the RVE is solved using an in–house implicit finite element solver for finite strain, considering all frictional contact interactions. A method is proposed to predict the bending moment’s evolution for any curvature variation from the simulation results of only one bending loading test on the RVE. The nonlinear behavior of the strand in the micro-scale identified through this offline technique can then be used in the macro-model to simulate various bending loading tests under constant tensile load. Results obtained with the multiscale model are compared to those provided by direct numerical simulation to demonstrate the validity of the proposed approach.

Reduction in Mode-I SIF of an Edge Cracked C-Shaped Specimen Using Piezoelectric Actuator

The focus of the current research is on the feasibility of an adhesively bound piezoelectric actuator in the active repair of an edge-cracked C-shaped specimen. First, only constant uniaxial tensile loading is used to determine the Mode-I stress intensity factor. The Mode-I stress intensity factor is then examined while taking into account the actuation effect provided by the piezoelectric patch when an external voltage is applied. For an edge-cracked C-shaped specimen, the total stress intensity factor is determined analytically using the concept of the superposition principle of the linear-elastic crack problem. The outcome demonstrates a considerable decrease in the Mode-I stress intensity factor following active repair using the piezoelectric actuator. Parametric analysis has been carried out to comprehend repair performance and choose the best-sized actuators for active repair.

Revealing the stress corrosion cracking initiation mechanism of alloy 718 prepared by laser powder bed fusion assessed by microcapillary method

Stress corrosion cracking (SCC) behaviour of L-PBF processed alloy 718 in chloride-containing solution was revealed, utilizing the microcapillary method under constant tensile loading. Results were compared with conventionally produced counterparts. Passive layer resistance was compared quantitatively by implementing electrochemical polarization experiments, in as-received and under tensile loading states. Superior corrosion and SCC resistance of L-PBF specimens under tensile loading were identified. Submicron cracks were initiated adjacent to the subgrain boundaries and the underlying mechanisms were elucidated as the synergistic effect of various microstructural factors. Data availabilityThe raw data with the findings of this article cannot be shared since there is ongoing research on this topic.

The Creep Properties of Paper

The creep properties of alpha-pup handsheets were determined at various constant tensile loads and relative humidities for the purpose of clarifying the prerupture mechanical behavior of paper.

The Creep Properties of Paper

The creep properties of alpha-pup handsheets were determined at various constant tensile loads and relative humidities for the purpose of clarifying the prerupture mechanical behavior of paper.

Characterising the stress ratio effect for fatigue crack propagation parameters of SAE 1045 steel based on magnetic flux leakage

The aim of this study was to determine the relationship between fatigue crack length, a, the number of cycles, N, the magnetic flux gradient intensity, dH/dx and the stress ratio, R. Fatigue crack growth tests were performed using a constant tensile load amplitude on SAE 1045 steel in the form of single-edge cracks. Stress ratio values of 0, 0.1, 0.2, 0.3 and 0.4 were used to study the characteristics of the magnetic flux gradient. A crack opening displacement device was used to detect the parameters of the stress intensity factor range, ΔK, fatigue crack growth rate, da/dN, and N. Meanwhile, a metal magnetic memory sensor device was used to detect the H value at the stress concentration zone when a 1 mm-increase in the crack occurred. The experimental results showed that as the fatigue cycle and crack length increased for each R, dH/dx also increased exponentially. The governing equations were derived based on the magnetic flux gradient for the fatigue crack length equation and the fatigue cycle equation, with the stress ratio. Based on a statistical analysis of the magnetic flux leakage signals, it was found that all the data were within a range based on a 90 % confidence level. Thus, the magnetic flux leakage parameters could be used to construct fatigue crack growth behaviour models for ferromagnetic materials and potentially as an alternative method for predicting the fatigue life.

Combined effects of stress and temperature on hydrogen diffusion in non-hydride forming alloys applied in gas turbines

Hydrogen plays a vital role in the utilisation of renewable energy, but ingress and diffusion of hydrogen in a gas turbine can induce hydrogen embrittlement on its metallic components. This paper aims to investigate the hydrogen transport in a non-hydride forming alloy such as Alloy 690 used in gas turbines inspired by service conditions of turbine blades, i.e. under the combined effects of stress and temperature. An appropriate hydrogen transport equation is formulated, accounting for both stress and temperature distributions of the domain in the non-hydride forming alloy. Finite element (FE) analyses are performed to predict steady-state hydrogen distribution in lattice sites and dislocation traps of a double notched specimen under constant tensile load and various temperature fields. Results demonstrate that the lattice hydrogen concentration is very sensitive to the temperature gradients, whilst the stress concentration only slightly increases local lattice hydrogen concentration. The combined effects of stress and temperature result in the highest concentration of the dislocation trapped hydrogen in low-temperature regions, although the plastic strain is only at a moderate level. Our results suggest that temperature gradients and stress concentrations in turbine blades due to cooling channels and holes make the relatively low-temperature regions susceptible to hydrogen embrittlement.

Robotic-Assisted Measurement of Fabrics for the Characterization of the Shear Tension Coupling

Industrial use of composite materials requires an increasingly advanced knowledge of technical textiles mechanical properties to control the manufacturing process and guarantee the performances of the finished products. Among the qualities that influence greatly the shaping process, theshear deformability is key for the forming of complex composite parts with double curves geometries. On the other hand, the stiffening of the behavior as the shearing rise is responsible for the occurrence of the wrinkling defect. This shearing behavior of the textile reinforcement is difficult to determinebecause it is non-linear and it coexists with a tensile stiffness of the fibers that is several orders of magnitude higher. Furthermore, shear and tension are coupled due to the weaving of the textiles. Now, few experimental methods have been proposed to measure the tension behavior of fabric as a function of its shear level because dedicated devices are needed for this investigation, capturing the shear-tension coupled behavior of fabric is then a difficult task. This paper deals with the robotization of the fabric shear-tension effect characterization. A KUKA robot associated with a force/torque sensor is utilized, taking advantage of its benefits in the ability to control the state of yarn tensions during shear tests while keeping track of the desired trajectory as enabled by the hybrid position-force control feature. This ensures precise positioning of a sample fabric and accurate contact forces. An anisotropic hyperelastic constitutive model for fabrics, based on the continuum theory of mechanics that takes into account the shear-tension coupling effect was formulated analytically and numerically simulated using Matlab software. An experimental test was then implemented to validate the proposed model. The results from a uni-axial tensile test and shear test under constant uni-axial tensile loading were obtained and analyzed to characterize the test sample. The model parameter identification was performed and presented in detail.

Failure life prediction for carbon nanotubes

Mechanical failure such as fatigue is a process with complexities arising from the microstructures of materials and the underlying physics. Single crystals without surfaces and imperfections thus offer an ideal platform to probe the process of mechanical degradation by excluding the microstructural complexity. We explore the failure mechanisms of single-wall carbon nanotubes under constant, monotonic and cyclic tensile loads. Simulations with the full-atom details show that, under high strain, failure is dominated by bond breakage, while bond recovery and Stone–Wales transitions are promoted as strain decreases or temperature increases. By assuming the process as a single-step or multiple-step reaction, kinetic models based on the Arrhenius law are developed for the process of mechanical degradation. The models well predict the life expectation and distribution, which conform to the exponential law for single-step processes and are complicated by the memory effect resulted from the multi-step mechanisms. We find that the nanotube could conform to the damage-free, memory-less limit dominated by bond breakage at room temperature and high strain, featuring an exponential distribution of life to failure, while at elevated temperatures where the Stone–Wales transitions are activated, the memory effect becomes significant and the life distribution can be better fitted by the log-normal or Weibull model. The work offers an atomistic view of the failure process and clarifies the underlying physics of the probabilistic models used for life prediction.