Yield Strength Point Research Articles

Investigation of the effect of initial magnetization state on the force-magnetic coupling effect of rebars

To investigate the effect of the initial magnetization state on the force-magnetic coupling effect of rebars, magnetic field magnetization experiments and axial tensile experiments of rebars were conducted. The tangential/normal components of spontaneous magnetic leakage field (SMLF) intensity BT/N were collected. The “SMLF intensity distribution parameters” DT/N were introduced to quantify the degree of stress-induced changes in the distribution of the BN/T curves on the rebar surface. The results show that both the stress state and the initial magnetization state affect the variation pattern of SMLF intensity of rebars, and BT/N have different characteristics of the force-magnetic coupling effect. With the increase of tensile stress, BT curves shift downward and BN curves rotate counterclockwise. With the increase of magnetization, the convexity degree of BT curves and the variation range of BN curves enlarge. And both BT/N values change abruptly at the yield strength point. The initial magnetization state drives the force-magnetic coupling effects in the elastic and plastic stages to exhibit differences. The σ-DT/N curves in the elastic stage are linearly monotonically decreasing, where the σ-DT fitted straight line has a large downward slope. DT is more sensitive to stress changes. The DT/N variations in the plastic stage can effectively characterize the stable development region of plastic deformation. The modified J-A magnetomechanical model reveals the contribution of the initial magnetization state to the characterization of the force-magnetic coupling effect. The morphological analysis of the rebar microstructure clarifies the physical reasons for the SMLF variation under different stress states. This research provides a new idea for the non-destructive detection of the rebar stress state.

Restoring force characteristic model for bending moment–rotation angle relationship of concrete‐filled square steel tube beam‐columns

AbstractThis paper proposes a new simplified restoring force characteristic model of the bending moment–rotation angle relationship for square concrete‐filled steel tube (CFT) beam‐columns to estimate the elastoplastic flexural‐shear behavior from short to slender beam‐columns. The square CFT beam‐column model incorporates a reduction in strength after the ultimate strength. The proposed simplified model is multilinear and involves a cracking strength point, a yield strength point, an ultimate strength point, and strength reduction points. In the proposed model, each flexural strength is calculated by a general superposed strength method, and new empirical expressions for each rotation angle are proposed from the results of previous experimental cyclic and monotonic loading tests. The proposed model for the bending moment–rotation angle relation is found to agree approximately with experimental results up to large rotation angles.

Mechanical Properties and Energy Dissipation Characteristics of Coal–Rock-Like Composite Materials Subjected to Different Rock–Coal Strength Ratios

The analysis of failure behaviors and energy dissipation characteristics of a coal–rock composite model is crucial to study mine dynamic disasters. A series of uniaxial loading and acoustic emission (AE) tests were implemented on coal–rock composite specimens with various rock–coal strength ratios (RCSRs). The results showed that the RCSR significantly affected the specimens' energy dissipation and mechanical characteristics. As the RCSR of the specimens increased, the failure mode of the rock–coal–rock specimens changed from shear failure to tensile failure. Based on the AE signal statistics, only one final failure occurred on the specimen with RCSR of 1:1, whereas the specimen with RCSR of 2:1–5:1 typically experienced coal failure first, followed by the final failure of the specimen. Energy dissipation and energy release are important causes of coal and rock damage. The energy dissipation coefficient curve had a significant peak value at the yield strength point, indicating that the dissipated energy began to increase quickly and that the specimen entered the unsteady failure stage with increasing loading. Moreover, the energy-storage limit and the final AE accumulative energy of specimens with different RCSRs showed that rock strength improved the specimens' non-deformability. The energy mechanism that drives crack growth and failure behavior was analyzed using energy theories and principles. The findings contribute to the study of coal and gas outbursts and dynamic disasters in coal mining activities.

Experimental and Numerical Analysis for the Mechanical Characterization of PETG Polymers Manufactured with FDM Technology under Pure Uniaxial Compression Stress States for Architectural Applications

This paper presents the numerical and experimental analysis performed on the polymeric material Polyethylene Terephthalate Glycol (PETG) manufactured with Fused Deposition Modeling Technology (FDM) technology, aiming at obtaining its mechanical characterization under uniaxial compression loads. Firstly, with the objective of evaluating the printing direction that poses a greater mechanical strength, eighteen test specimens were manufactured and analyzed according to the requirements of the ISO-604 standards. After that, a second experimental test analyzed the mechanical behavior of an innovative structural design manufactured in Z and X–Y directions under uniaxial compression loads according to the requirements of the Spanish CTE standard. The experimental results point to a mechanical linear behavior of PETG in X, Y and Z manufacturing directions up to strain levels close to the yield strength point. SEM micrographs show different structural failures linked to the specimen manufacturing directions. Test specimens manufactured along X present a brittle fracture caused by a delamination process. On the contrary, test specimens manufactured along X and Y directions show permanent plastic deformations, great flexibility and less strength under compression loads. Two numerical analyses were performed on the structural part using Young’s compression modulus obtained from the experimental tests and the load specifications required for the Spanish CTE standards. The comparison between numerical and experimental results presents a percentage of relative error of 2.80% (Z-axis), 3.98% (X-axis) and 3.46% (Y-axis), which allows characterizing PETG plastic material manufactured with FDM as an isotropic material in the numerical simulation software without modifying the material modeling equations in the data software. The research presented here is of great help to researchers working with polymers and FDM technology for companies that might need to numerically simulate new designs with the PETG polymer and FDM technology.

コンクリート充填角形鋼管柱・鉄骨梁接合部パネルの弾塑性性状に関する研究

This paper proposes a new practical model of a restoring force characteristic on the panel zone within steel beam-to-concrete filled square steel tube column moment connections for predicting the elastoplastic behavior of the panel zones including strength reduction after ultimate strength. The proposed model for a skeleton curve is provided as a multi-linear model having a cracking strength point, a yield strength point, an ultimate strength point and strength reduction points for 95%, 90% or 80% of ultimate strength. The skeleton curve model up to the ultimate strength point is based on the previous shear force-deformation model proposed by the writers, while the deformations of these strength reduction points is provided as new regression formulations obtained from previous test results. The writer proposes a new hysteresis loop model including stiffness reduction. The proposed models agree approximately with experimental results up to large deformations.

Multi-linear stress–strain and closed-form moment curvature response of epoxy resin materials

A simplified multi-linear stress–strain approach has been used to obtain the closed form nonlinear moment curvature response for epoxy resin materials. The model consists of constant plastic flow in tension and compression. The multi-linear stress–strain model is described by two main parameters in addition to four non-dimensional tensile and six non-dimensional compressive parameters. The main parameters are modulus of elasticity in tension and strain at the proportional elastic limit point in tension. The ten non-dimensional parameters are strain at the ultimate tensile stress, maximum strain, post elastic proportionality stiffness, and post peak strength in the tension model and strain at the proportionality elastic limit, strain at yield strength point, maximum strain, initial elastic stiffness, post elastic proportionality stiffness, and post peak strength in the compression model. Explicit expressions are derived for the stress–strain behavior of the epoxy resins. Closed form equations for moment curvature relationship are presented. The results of tension, compression, and bending tests using digital image correlation technique are presented. Load deflection response of flexural three point bending (3PB) samples could be predicted using the moment curvature equations, crack localization rules, and fundamental static equations. The simulations and experiments reveal that the direct use of uniaxial tensile and compressive stress–strain curves underestimates the flexural response. This model gives an upper bound estimate for flexural over-strength factor.

Elastoplastic Behavior of Panel Zone in Steel Beam-to-Concrete Filled Steel Tube Column Moment Connections

Subassemblage tests were conducted on the panel zone within steel beam-to-concrete filled steel tube (CFT) column moment connections made from high-strength material to investigate their elastoplastic behavior. The writers propose a nonlinear shear force-deformation model for the panel zone in beam-to-column CFT connections for predicting the elastoplastic behavior of the panel zones. The proposed model includes a superposed model based on a trilinear shear-deformation relationship for the steel tube superposed on one for the concrete core, and a simple model provided as a trilinear model having a yield strength point and an ultimate strength point for this panel zone, as a practical model for design. The writers also propose a method for evaluating load resistance, in which a new theoretical compression strut mechanism is utilized, taking into account the confinement of the tube flange. The results predicted using the superposed and the simple model are found to agree approximately with the experimental results up to a large shear deformation of 0.04 rad.