Effect Of Strength Degradation Research Articles

Modified nonlinear cumulative damage model considering residual strength degradation and gear reliability analysis

AbstractThe fatigue damage of gear is caused by the coexistence and mutual influence of residual strength degradation and cumulative damage. The residual strength decreases continuously with the change of the loads and the increase of stress cycles. Most of the traditional cumulative damage models ignore the effect of residual strength degradation on cumulative damage. The exponential parameter in the traditional Corten‐Dolan model was defined as exponentials function related to the strength degradation coefficient, and the strength degradation coefficient was deduced by analyzing the residual strength degradation model, and the modified Corten‐Dolan model considering the residual strength degradation was established. Based on the stress‐strength interference model, a gear reliability model considering residual strength degradation was established. The effectiveness of the strength degradation model and the accuracy of the modified Corten‐Dolan model are verified by the analysis of the test data, which provides a new idea for the reliability analysis of gear. The accuracy of the gear reliability model proposed in this paper was verified by Monte‐Carlo (M‐C) simulation, which has practical significance for engineering application.

Cyclic performance of severely earthquake-damaged RC bridge columns repaired using grouted UHPC jacket

The bridges constructed in high seismic zones may suffer one or more earthquake shocks of certain scales during their service life. Some of them could be severely damaged during a catastrophic earthquake event. How to quickly and economically restore bridge service functions and traffic lifelines has always been the concern of bridge owners and engineers. In this study, a method for repairing seismically damaged reinforcement concrete (RC) bridge columns using ultrahigh performance concrete (UHPC) materials was developed. Seven down-scale RC bridge column specimens with three different reinforcement ratios and two different heights were designed according to the seismic design code for RC bridges. For three of the specimens, the reinforcement around the plastic hinge area were artificially corroded through chloride ion penetration method to simulate the strength degradation effect of reinforcement erosion that could occur in many aging bridge columns. All seven specimens were tested by applying cyclic loads until their plastic hinge became severely damaged, which were then repaired following the proposed procedure and with different jacket thicknesses. The cyclic tests were re-conducted for these repaired specimens. The testing results were analyzed by comparing to those from the test for the non-seismic-damaging specimens one by one with respect to their seismic performance in order to validate the seismic rehabilitation effect using UHPC materials. Additionally, an ABAQUS software based finite element model was developed for numerically simulating the hysteretic behaviors of the columns repaired using UHPC jacket. The resulting hysteretic curves for the repaired columns with different reinforcement ratios and heights well matched those from the corresponding cyclic tests. This model can be further used for seismic performance prediction and UHPC jacket design for the repaired bridge columns that have different dimensions and reinforcement configurations. All of these experimental and analytical results show that the seismic performance of the repaired bridge columns can be effectively restored in a relatively fast and low-cost manner.

Experimental and Numerical Investigations on Seismic Performance of CFST Frame with External Diaphragm Joint

This paper aims to investigate the seismic performance of a steel frame with an external diaphragm joint between a concrete-filled steel tube (CFST) column and H-shaped steel beam through experiments and finite-element (FE) analysis. A quasistatic test was conducted on five steel frame specimens. The parameters involved in the test were joint stiffness, beam-to-column stiffness ratio and concrete strength. Based on the experimental results, failure mode, lateral load versus displacement hysteretic curve, skeleton curve, strength and stiffness degradation effects, ductility, and energy dissipation capacity were analyzed. The experimental results show the hysteretic curves have a plump shuttle shape; the strength degradation effect and stiffness degradation effect are relatively feeble; and the ductility and energy dissipation capacity are excellent. Therefore, the tested specimens have good seismic performance. Also, this suggests that larger joint stiffness brings about superior seismic performance; a stronger column leads to higher bearing capacity as well as inferior ductility and energy dissipation capacity; and a CFST frame performs better than a hollow steel tube column frame under cyclic loads. On the basis of the experimental results, the ABAQUS software version 6.14 was adopted to establish the FE models. The applicability and accuracy of FE simulation were first verified by experimental results. Then, quantitative parametric analysis was carried out to study the effects of different parameters on seismic performance of the CFST frame with an external diaphragm joint.

Deterioration characteristics of cement-improved loess under dry-wet and freeze-thaw cycles.

The effects of cement dosage, compaction coefficient, molding method (vertical vibration method and static pressure method), and dry-wet and freeze-thaw cycles on the mechanical strength of cement-improved loess (CIL) were studied to reveal its strength degradation law under dry-wet and freeze-thaw cycles. Results show that when using the vertical vibration molding method, the strength degradation effect of CIL can be improved by increasing the cement dosage and compaction coefficient; however, it is not obvious. Under the action of dry-wet cycle, damages, such as voids and cracks of CIL, develop continuously. Further, the strength deteriorates continuously and does not decrease after more than 15 dry-wet cycles. Therefore, the dry-wet cycle degradation system is selected by considering the most unfavorable conditions. In the process of freeze-thaw alternation, the pores and fissures of CIL develop and evolve continuously and the strength deteriorates continuously under the joint influence of water and low temperature. The strength tends to become stable after more than 12 freeze-thaw cycles. According to the safety principle, the deterioration coefficient of the freeze-thaw cycles is 0.3.

An out-of-plane bending hysteretic model for multi-planar CHS X-connections

The multi-planar circular hollow section (CHS) X-connection is one of common configurations in single layered lattice steel tubular structures. A hysteretic model, including the skeleton model and restoring force model is proposed to simulate the hysteretic performance of X-connections under cyclic out-of-plane bending moments (OPB) generated by vertical seismic action. Exponential function is adopted in the skeleton model and the Ramberg-Osgood function is adopted in the restoring force model. The parameters in the hysteretic model are determined by finite element (FE) analysis and nonlinear regression. Additionally, an improved out-of-plane bending hysteretic model considering the influence of brace axial stress and chord normal stress is developed to simulate the seismic performance of X-connections in engineering practice. The proposed hysteric model is verified by experimental and FE results and the improved hysteretic model can consider the effect of strength degradation.

The fatigue life study of polyphenylene sulfide composites filled with continuous glass fibers

In this study, an effective microscopic model is proposed to investigate the fatigue life of composites containing continuous glass fibers, which is surrounded by polyphenylene sulfide (PPS) matrix materials. The representative volume element is discretized by parametric elements. Moreover, the microscopic model is established by employing the relation between average surface displacements and average surface tractions. Based on the experimental data, the required fatigue failure parameters of the PPS are determined. Two different fiber arrangements are considered for comparisons. Numerical analyses indicated that the square edge packing provides a more accuracy. In addition, microscopic structural parameters (fiber volume fraction, fiber off-axis angle) effect on the fatigue life of Glass/PPS composites is further discussed. It is revealed that fiber strength degradation effects on the fatigue life of continuous fiber-reinforced composites can be ignored.

A Simple Effective Stress Approach for Modeling Rate-Dependent Strength of Soft Clay

This paper proposes a simple effective stress method for modeling the strain rate-dependent strength behavior that is experienced by many fine-grained soils in offshore events when subjected to rapid, large strain, undrained shearing. The approach is based on correlating the size of the modified Cam-Clay yield locus with strain rate, i.e., yield locus enlarging or diminishing dependent on the strain rate. A viscometer-based method for evaluating the needed parameters for this approach is provided. The viscometer measurements showed that strain rate parameters are largely independent of water content and agree closely with data from a previous study. Numerical analysis of the annular simple shear situation induced by the viscometer shows remarkable agreement with the experimental data provided the remolding-induced strength degradation effect is accounted for. The proposed method allows offshore foundation installation processes such as dynamically installed offshore anchors, free-falling penetrometer, and submarine landslides to be more realistically analyzed through effective stress calculations.

Collapse period of degrading SDOF systems

Seismic demand estimation for a structure is a critical issue for seismic performance assessment so that the potential damage can be estimated realistically. Many researchers proposed simplified methods to estimate the demand of a structure under strong ground motions. However, most of them did not consider degradation and collapse potential of the structures. Even some of theme considered the degradation effect, stiffness and strength degradation effects were considered separately without collapse potential caused by dynamic instability. In this study, collapse potential of SDOF systems caused by dynamic instability with stiffness and strength degradation has been investigated. Nonlinear time history analyses were performed, using an energy-based, strength and stiffness degraded hysteretic model that considers the collapse potential, with 160 earthquake acceleration time histories. An equation was proposed for the estimation of collapse period of SDOF systems as a function of certain strength reduction factor, ductility level and post-capping stiffness ratio. Finally, effects of parameters of the considered hysteretic model and local site conditions on the collapse period were investigated.

Geomechanical and water vapor absorption characteristics of clay-bearing soft rocks at great depth

The geological and physico-mechanical properties characterization of deep soft rocks is one of the critical scientific issues for deep soft rock engineering. In the present study, X-ray diffraction (XRD) analysis, scanning electron microscope (SEM), and mercury intrusion porosimetry experiments were carried out to investigate the mineral compositions, microstructure and porosity characteristics of the 13 clay-bearing soft rock samples collected from a deep coal mine in China. Water vapor absorption and uniaxial compressive experiments were also performed to examine water absorption characteristics and water-induced strength degradation effect of the investigated deep soft rock samples. The results show that the dominant mineral components in mudstone, coarse sandstone and fine sandstone samples were calcite, quartz and clay respectively. The contents of clay minerals in all samples were relatively high and ranged from 12.3% (N-4) to 56.5% (XS-1). Water vapor absorption processes of all the soft rock samples follow an exponential law which is very similar to the water vapor absorption behavior of conglomerate samples reported in our earlier study. Correlation analyses also suggested that there were good positive correlation relationships between water absorptivity and clay minerals for both mudstone and sandstone samples. Furthermore, it was found that vapor absorption was not correlated with the porosity for mudstone, however, positive correlation relationship was found between them for sandstone. Correlation analysis between UCS, modulus of elasticity and water content demonstrated that both of them tend to decrease with the increase of their water content due to water absorption.

Strength degradation and failure limits of dense and porous ceramic membrane materials

Abstract Thin dense membrane layers, mechanically supported by porous substrates, are considered as the most efficient designs for oxygen supply units used in Oxy-fuel processes and membrane reactors. Based on the favorable permeation properties and chemical stability, several materials were suggested as promising membrane and substrate materials: Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3− δ , La 0.6− x Sr 0.4 Co 0.2 Fe 0.8 O 3− δ ( x = 0, 0.02) and Ce 0.9 Gd 0.1 O 1.95− δ . Although membranes operate at elevated temperatures, the ends of tubes in certain three-end concepts remain almost at room temperature. The current work concentrates on the failure potential of these membrane parts, where in a complex device also the highest residual stresses should arise due to differences in thermal expansion. In particular, sensitivity of the materials to subcritical crack growth was assessed since the long-term reliability of the component does not only depend on its initial strength, but also on strength degradation effects. The results were subsequently used as a basis for a strength–probability–time lifetime prediction.

Reliability Optimization Design for Mechanical Components

The traditional reliability model of mechanical components can not well reflect the effect of strength degradation on reliability。In the paper, A new method is applied to develop a dynamic reliability model of mechanical components considering the strength deterioration with time passing。The calculated result s by a real example show that could not only calculate the failure probability of the response, but also could make the process of optimization of the response under the conditions of meeting reliability restraint.

Series System Failure Rate Modeling and the Mechanism to Yield Bathtub Curve

Failure rate functions were usually constructed in terms of life distribution. The present paper defines “discrete failure rate”, analyzes the dependence of failure rate curve shape on the probabilistic property of load-strength interaction, and develops load-strength-interaction based system failure rate model. For the majority of mechanical equipment, operation load is normally a random process, components are subjected to a large number of stochastic load actions during its service life. Meanwhile, material property degrades continuously owing to the failure mechanisms such as fatigue. It is the ever changing load-strength relationship that yields the variation in failure rate. Based on the criterion that failure occurs when a load higher than the relevant strength appears, failure rate model is developed based on the interaction mechanism between load and residual strength, and their statistical characteristics as well. Based on the interpretation to the variation of failure rate in terms of load uncertainty and strength uncertainty, the effect of statistical risk of load and the effect of strength degradation on failure rate curve shape are highlighted.

Evaluation on the Compressive Strength of Concrete Incorporating High Volume Blast-Furnace Slag Subjected to Initial Frost Damage

Construction works that uses concrete incorporating a high volume of blast-furnace slag (BFS) during the winter season increases the risk of being subjected to initial frost damage as it noticeably delays setting and hardening. Assuming that the concrete incorporating a high volume of BFS was affected by freezing at an early age during the winter conditions, this study is to investigate the effect of strength degradation by early freezing and curing methods on compressive strength. As a result, freezing at early age highly degraded the compressive strength regardless of the types of concrete. After influenced by initial frost damage, water curing at 5°C improved the long-term strength and water curing at 30°C enhanced the long-term strength as well as the early strength.

Enhanced Displacement Coefficient Method for Degrading Multi-Degree-of-Freedom Systems

The displacement coefficient method proposed in FEMA 440 was evaluated using response statistics from a comprehensive set of nonlinear simulations of multi degree of freedom systems under both far-fault and near-fault ground motions. The study finds that it is practically difficult to achieve high relative strength factors ( R values equal to or greater than 6.0) for very stiff systems thereby dictating the need to define R-dependent demand coefficients. The approximate expressions proposed in FEMA 440 for the C2 coefficient is shown to underestimate the displacement demand of stiffness-degrading short period systems. Additional nonlinear simulations were performed to investigate the combined effect of strength degradation and P-Delta effects on the displacement demands of MDOF systems. A new expression for the modification factor that reflect combined P-Delta and degrading effects for the estimation of displacement demands is proposed.

Hemivariational Inequality Modeling of Hybrid Laminates with Unidirectional Composite Constituents

Theoveralltensileandbendingbehaviorofunidirectionalcompositeelementswithmonotoneandnonmonotone, possibly multivalued,constitutive laws foreach constituent arestudied within a nonsmooth mechanics framework. A nondifferentiable and possibly nonconvex, caused by degradation effects, potential energy is formulated for the whole mechanical system. For the structural analysis problem the potential energy minimization problem is considered. The arising variational or hemivariational (in the case of nonmonotone laws ) inequality problems are solved by appropriate nonconvex-nonsmooth computational mechanics techniques. Parametric numerical investigations of typical composite elements are presented, which shed light into the complex behavior of the composite structural elements. On the other hand, the arising overall laws can be used as phenomenological laws for structural analysis of large-scale structures incorporating the studied composite elements. I. Introduction C OMPOSITE materials is a rapidly maturing technology with emerging applications in a wide range of industries far beyond the aerospace domain where they e rst became popular. Nowadays, composites are popular even in the civil-engineering domain and are used for the construction of light bridges, domes, space trusses, etc. Moreover, composite elements are used in structures that are susceptible to electrochemical actions or corrosion, such as underground facilities, offshore oil platforms, waterways, and harbors. 1 The basic principles involved in the design of structures made of compositematerialsarethesameasthoseofisotropicmaterialssuch as steel. The classical theories and methods of analysis can be used for the design ofcomposite structures, asfar as the constitutive relationship takes into account the material anisotropy and the strength degradation effects, which are present in the majority of composite materials. Moreover, the same basic design knowledge and technique used for other materials as, e.g., for reinforced concrete, can be applied to compositestructures.However, thereader shouldhave inmindthattheimplementationofaccuratedesignmethodsforsteel (which is the materialwith the most simple constitutive relationship used today in civil-engineering structures ) has required a century of research and experience. In this framework it is not only very important to study these new materials at the materials level, but it is also very important to know their behavior at the structural level. (Compare in this respect the combined effects in the study of beam-to-column connections in steel structures, which lead to strong nonlinearities.) Also, the phenomenological (macroscopic ) response under certain types of loading is of great importance. In unidirectional composites the e bers are aligned in one only direction, thus achieving the maximum e ber alignment and the maximum e ber content. As in principle, the strength of a composite structural element increases in proportion to increasing e ber content, this type of composite provides high strength to the direction of the e bers but very low transverse strength. Therefore it is very common to combine unidirectional composite materials in a cer

Seismic [formula omitted] effects in mesium height moment resisting steel frames

An analytical investigation of the P- Δ effects in medium height steel moment resisting frames to selected earthquake motions is reported. The frames with various design drifts and fundamental natural periods were designed according to the load provisions for New Zealand seismic risk zone A of the Draft Code of Practice for General Structural Design and Design Loading for Buildings, DZ4203. The effect of strength degradation was investigated. Dynamic magnification factors for the member forces and displacement are also presented. Limits for the maximum plastic hinge rotation, inelastic drift, curvature ductility, displacement ductility and prediction of maximum plastic hinge rotation based on the inter-storey drift are suggested.

P-delta effects in medium height moment resisting steel frames under seismic loading

An analytical investigation of the P-delta effects in medium height steel moment resisting frames excited by selected earthquake motions is reported. The frames with various design drifts and fundamental natural periods of free vibration were designed according to the loadings provisions for New Zealand's highest seismic risk zone (Wellington) of the Draft Code of Practice for General Structural Design and Design Loading for Buildings, DZ4203 [10] as issued as a "Draft for Comment" in May 1986. The effect of strength degradation was investigated. Dynamic magnification factors for the member forces and displacement were also observed. Limits for the maximum plastic hinge rotation, inelastic drift, displacement magnification and prediction of maximum plastic hinge rotation based on the inter storey drift are suggested.

Effect of strength degradation on wear and friction

AbstractA theoretical expression for wear rate as a function of sliding velocity has been formulated from the concepts of crack propagation, thermal activation, and strength degradation and the analytic results have been tested against the experimental data to provide a comprehensive understanding of this complex behavior. A similar equation describing the relationship between the wear rate and normal load has also been provided. The coefficient of friction has been analyzed theoretically as a function of normal load and sliding velocity and compared with the experimental results. The coefficient of adhesion has given an expression by employing two approaches: average crack propagation velocity and atomic residence time concepts. Consideration of strength degradation has led to a wear rate equation which does explain the experimental result satisfactorily for polymer composites. Some thoughts has been given to the atomic chain orientation effect on wear and friction, and also the boundary lubrication phenomena have been described briefly.