Monotonic Loading Conditions Research Articles

A temperature-dependent asymmetric constitutive model for cast irons under cyclic loading conditions

An elastic-plastic-creep constitutive model is developed for describing the asymmetric deformation behaviour of cast irons under tensile and compressive loading conditions for a wide range of temperatures. The model is implemented into two commercial finite element packages, PERMAS and ABAQUS, using FORTRAN subroutines. The model is then employed for representation of the deformation behaviour of a flake cast iron under isothermal monotonic and thermomechanical cyclic loading conditions. Good agreement between the model representation and experimental data is obtained. Ultimately, the developed model is employed for assessment of the stress state at critical locations of a diesel engine cylinder head subjected to a severe thermal-shock engine test.

Strength degradation of sandstone and granodiorite under uniaxial cyclic loading

Change in mechanical properties of rocks under static loading has been widely studied and documented. However, the response of rocks to cyclic loads is still a much-debated topic. Fatigue is the phenomenon when rocks under cyclic loading fail at much lower strength as compared to those subjected to the monotonic loading conditions. A few selected cored granodiorite and sandstone specimens have been subjected to uniaxial cyclic compression tests to obtain the unconfined fatigue strength and life. This study seeks to examine the effects of cyclic loading conditions, loading amplitude and applied stress level on the fatigue life of sandstone, as a soft rock, and granodiorite, as a hard rock, under uniaxial compression test. One aim of this study is to determine which of the loading conditions has a stronger effect on rock fatigue response. The fatigue response of hard rocks and soft rocks is also compared. It is shown that the loading amplitude is the most important factor affecting the cyclic response of the tested rocks. The more the loading amplitude, the shorter the fatigue life, and the greater the strength degradation. The granodiorite specimens showed more strength degradation compared to the sandstone specimens when subjected to cyclic loading. It is shown that failure modes of specimens under cyclic loadings are different from those under static loadings. More local cracks were observed under cyclic loadings especially for granodiorite rock specimens.

Effect of PWHT with Sheet-Type Ceramic Heater on Compressive Behaviors of Non-Stiffened Welded Steel Box Columns

A series of fundamental experimental investigation was conducted in order to examine the effect of PWHT by sheet-type ceramic heater on the residual stress, deformation and compressive behavior of non-stiffened welded box columns. The sheet-type ceramic heater was able to control the required temperature history for PWHT with high accuracy. The welding-induced tensile and compressive residual stresses of the specimens were reduced by 90% and 76% respectively with PWHT. Besides, PWHT could reduce the welding-induced out-of-plane deformation by 22%. It was revealed that the PWHT specimens had a slight higher stiffness than the As-welded specimens when applying monotonic static compressive load on both As-welded and PWHT specimens. They could also enhance the ultimate compressive load capacity about 32% of that of the As-welded specimens. The effectiveness of PWHT with the sheet-type ceramic heater could be confirmed.

Numerical modelling of innovative DST steel joint under cyclic loading

This paper addresses the numerical simulation of an innovative double split Tee beam-to-column joint fitted with a dissipative friction damper, recently proposed at the University of Salerno. The innovative connection prevents damage to all other structural components with the exception of one component of the connection that is specially designed to dissipate the input energy of a seismic hazard by means of the slippage of a friction material. The main topics herein presented are the development of a strategy for the numerical modelling of complex friction problems and a detailed numerical model of the overall beam-to-column joint equipped with the friction device. The joint is subjected to both monotonic and cyclic loading conditions. The numerical modelling was developed using the Finite Elements Method (FEM) with Abaqus Software. Sliding force–displacement curves are obtained for two damper materials and an estimation of their wearing is presented. To evaluate the accuracy of the numerical model, moment–rotation curves of the joint are compared with the experimental curves. The FE results show good correlations and confirm the potential interest of this novel joint typology to achieve easily replaceable details in case of a seismic event.

A return mapping algorithm for elastoplastic and ductile damage constitutive equations using the subloading surface method

AbstractIn this paper is presented a return mapping algorithm for an elastoplastic/damage model that couples the constitutive equations of an unconventional plasticity model with the phenomenological description of ductile damage in the continuum damage mechanics framework. This approach combines the advantages of describing the mechanical property degradation by using the Lemaitre model with the realistic accumulation of plastic deformation in cyclic mobility problems from the subloading surface model. Most of the damage models for ductile failure focus on monotonic loading conditions, whereas the present model aims to extend the investigation to cyclic loading and low‐cycle fatigue problems. A cutting‐plane algorithm is adopted to describe the material behavior that considers both isotropic and kinematic hardening laws. Two simple numerical studies show that the elastoplastic and damage model is implemented correctly, displaying a quadratic rate of convergence for local equilibria and precise solutions, even for large‐prescribed strain increments.

Stress–strain evaluation of steel‐strapped high‐strength concrete with modified self‐regulating end clips

High‐strength concrete (HSC) is increasingly used in columns of building all over the world. Although it offers superior properties, it is relatively a brittle material. This study intends to improve the ductility of HSC using modified pretensioning confinement technique. It investigates the effects of the technique on the performance of the column and develops equations to predict the stress–strain. The basis of the technique is to apply a pretensioning force to relatively low‐cost steel straps wrapped around the specimens. A modified end clip which is able to be self‐regulated is used to secure the strap ends. The parameters studied include various spacing between straps and number of layers of straps. The confined specimens were tested in compression until failure under monotonic loading conditions, focusing particularly on the mode of failure, loads at peak and ultimate conditions and longitudinal and lateral strains in both concrete and straps. It was observed that the pretensioning technique using steel straps enhanced the ductility as well as the strength of the concrete as the confining ratio increases. Moreover, the layers of straps had also delayed the onset of volumetric expansion and therefore, the concrete failure. Based on the regression analysis, new equations of strength and strain for the confined HSC column have been developed to predict its stress–strain behavior.

Simulation of ductile fracture toughness test under monotonic and reverse cyclic loading

This paper presents a ductile crack growth simulation method for monotonic and reverse cyclic loading with large-scale yielding using the damage model based on the multi-axial fracture strain energy. The damage model has two parameters which can be determined from tensile and fracture toughness data under the monotonic loading condition. The determined damage model then can be used to simulate ductile crack growth subjected to reverse cyclic loading with large-scale yielding. The proposed method is validated against test data for SA508 Gr.1a and TP316 under monotonic and reverse cyclic loading with three different reverse loading ratios.

Cracking of quasi-brittle structures under monotonic and cyclic loadings: A d+/d− damage model with stiffness recovery in shear

In the present paper, a new d+/d− damage model apt for quasi-brittle materials is described and its validation is carried out considering unreinforced concrete, reinforced concrete and masonry elements.Two independent scalar damage variables, d+ and d−, in combination with the split of the reversible strain tensor into its positive and negative counterparts, are adopted in order to simulate the pronounced dissimilar response under tension and compression, typical of these materials. An energy-equivalent framework is considered for representing the orthotropy induced in the material by the degradation process, with the consequence that a thermodynamically consistent constitutive operator, positive definite, symmetric and strain-driven, is derived. In addition to the degradation parameters, the permanent strain tensor is also contemplated by the model and a modification of the exponential softening modulus is proposed in order to treat the evolution of the two causes of dissipation, damage and irreversible deformations, in a coupled way.The formulation is integrated with a multidirectional damage procedure, addressed to extend the microcrack closure-reopening (MCR) capabilities of the model to shear cyclic conditions, characterized by orthogonal (or however intersecting) sets of cracks. Maintaining unaltered the dependence of the constitutive law from two scalar indeces, d+ and d−, this approach activates or deactivates a tensile (compressive) damage value on the base of the current maximum (minimum) principal strain direction. In correspondence with damage activation (crack opening) or deactivation (crack closure), a smooth transition is introduced, in order to avoid abrupt changes in stiffness and enhance the numerical performance and robustness of the multidirectional procedure. The adequacy of the proposed constitutive model in reproducing experimental results has been proven for both monotonic and cyclic loading conditions. The two examples of application involving cyclic loads, dominated by shear, constitute a validation of the multidirectional damage approach, showing how the suitable representation of unilateral effects and permanent deformations is essential to model the observed structural response in terms of maximum resistance, evolution of stiffness degradation and dissipation capacity.

Cyclic performance of bolted cruciform and splice connectors in retrofitted transmission tower legs

Aging transmission towers are increasingly being found to have insufficient strength to meet increased design wind loads and additional electricity demands. One potential solution is to strengthen old tower members through adding new structural components. The bolted cruciform connector is an effective load-transferring component for members that combine new and old components. This paper addresses the cyclic performance of bolted cruciform and splice connectors in retrofitted transmission towers through a series of experimental tests. One type of 12-bolt splice connector and one type of 8-bolt cruciform connector were designed and two groups for each type were tested under monotonic and cyclic loading conditions. Key parameters including bolt pretension, bolt-slip load and dynamic stiffness with varying load amount, frequency and cycle number were investigated. Experimental results showed that the cyclic loadings reduce bolt-slip load and static structural stiffness of cruciform and splice connectors due to the surface smoothening and bolt pretension loss. The bolt pretension and bolt-slip load continuously reduced with the increase of loading cycle numbers and loading magnitudes. However, the static bolt-slip load was not found to be sensitive to varying loading frequencies. Finally, practical prediction equations were developed in terms of cyclic loading parameters for both connectors. The prediction equations showed strong agreement with experimental results in both low and high loading magnitudes under varying loading conditions.

Design and static behavior of beam-to-beam-tied connection for modular steel buildings

Modular steel building(MSB) is the high-end prefabricated building product with outstanding advantages of high assembly rate and environmental friendliness. Specially, the connections between modules are critical parts that can strongly influence the overall structural stability and robustness. This study presented an innovate MSB connection design that has the intermediate plug-in device and beamto-beam bolting system as horizontal and vertical connecting respectively. Detailed connecttion and features for MSBs were introduced. Then static behaviors of the different position connection were investigated through static monotonic loading tests, including one direction corner connection and two direction inner connection. Effect of diagonal stiffener was discussed trough experimental tests. Results showed that gaps formed between upper and bottom columns can influence the deforming patterns and bending demand distributions at each unit joints

Void coalescence mechanism for combined tension and large amplitude cyclic shearing

Void coalescence at severe shear deformation has been studied intensively under monotonic loading conditions, and the sequence of micro-mechanisms that governs failure has been demonstrated to involve collapse, rotation, and elongation of existing voids. Under intense shearing, the voids are flattened, such that the void volume diminishes, whereafter the flattened crack-like voids rotate and elongate until interaction with neighboring micro-voids dominates the material response and coalescence sets in. Eventually, this leads to a complete loss of load carrying capacity. The severe shear loading, imposed at the far boundary, is in an early state of the deformation associated with significant stretching of parts of the void surface, while other parts remain practically un-deformed. A largely uneven distribution of the strain hardening, therefore, evolves along the void circumference and, thus, one cannot expect the void to return to its original shape in the case where the far-field loading is reversed. The present numerical work aims to investigate the evolution of micro-voids subject to constant tension and large amplitude cyclic shearing. The far-field loading, the void shape, and the void growth are monitored, and the calculations are pushed to coalescence and complete loss of load carrying capacity. The initially circular cylindrical voids are predicted to develop protrusions in the shearing plane with normal in the direction of the applied tensile load. These protrusions evolve during repeated cyclic shearing and spread towards neighboring voids - eventually being responsible for void coalescence.

Anti-progressive collapse behavior of beam-to-column assemblies with bolted-angle connections under different span ratios

This article discusses the anti-progressive collapse performance of three specimens, with top-seat angles with double web-angle connections, under different span ratios. Double full-span assemblies extracted from steel frames with a typical column-removal scenario were designed and applied in a monotonic static loading experiment. The failure modes/sequences, strain, internal force conditions, and the transformed law of the resistance mechanism are examined. The results obtained show that specimens with equal spans can provide greater resistance due to full development of flexural and catenary actions. For specimens with unequal spans, the catenary resistance from the short beam portion is larger than that from the long beam portion, and the asymmetry of the span is not beneficial to the structure’s bearing capacity in preventing progressive collapse. The three specimens’ dynamic increase factors are also discussed in terms of the energy balance principle and their development trend for nonlinear static a...

On catastrophic fracture of steel structures at temperatures lower than cold brittleness threshold

The paper considers crack propagation in elements of homogeneous steel structures and those with welded joints. For analysis of failure of the structures, diagrams of quasi-brittle fracture have been plotted. When constructing quasi-brittle fracture diagrams, the model of elastic-plastic material having an ultimate strain was used. The data report for quasi-brittle fracture diagrams of common elements of structures has been given. Analysis of parameters used in the proposed model was carried out for temperatures near or lower the brittleness threshold. Parameters of the model are selected from two laboratory experiments (critical stress intensity factor and classical stress-strain diagram) performed at appropriate temperatures. It has been established that weld structures with cracks in the vicinity of a welded joint exhibit decreased crack toughness. The effect of structure break under monotonic loading conditions is clearly visible inasmuch as ultimate loads essentially decrease with increasing a crack length. The attention is given to the parameter characterizing plastic material deformation and exhaustion of plasticity resource under preliminary plastic material deformation. After the plasticity resource is exhausted, the temperature of brittleness threshold approaches a room temperature.

Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

A hypo-plastic approach for evaluating railway ballast degradation

Repetitive or cyclic rail loading deteriorates the engineering properties of the railway ballast by particle crushing and rearrangement. Most of the classical elasto-plastic models are unable to predict such ballast degradation despite successfully predicting the overall load–deformation behavior during cyclic densification. In this context, the present study delivers a novel hypo-plastic modeling approach coupled with breakage mechanics theory to bridge the gap of the conventional models. The hypo-plastic approach enables to predict the nonlinear load–deformation response of ballast-type granular materials for both monotonic and cyclic loading conditions, while circumventing the requirement of notional yield condition to predict the inelastic behavior. Breakage mechanics theory, on the other hand, establishes the links between particle comminution and the macroscopic deformation. The novelty of the proposed approach is threefold. Firstly, unlike the conventional hypo-plastic approaches, the development of the proposed model is within the continuum thermodynamics framework. Secondly, the model requires less number of physically identifiable parameters as compared to that of earlier models employed for assessing the particle breakage under cyclic loading. Third and finally, the numerical implementation of the model as a user-defined material is simple for solving boundary value problems. Under the compressive deformation regime, the model prediction of the ballast degradation along with the cyclic densification response agrees reasonably well with the experimental results found in the literature.

Finite element based contact analysis of radio frequency MEMs switch membrane surfaces

Finite element simulations were performed to determine the contact behavior of radio frequency (RF) micro-electro-mechanical (MEM) switch contact surfaces under monotonic and cyclic loading conditions. Atomic force microscopy (AFM) was used to capture the topography of RF-MEM switch membranes and later they were analyzed for multi-scale regular as well as fractal structures. Frictionless, non-adhesive contact 3D finite element analysis was carried out at different length scales to investigate the contact behavior of the regular-fractal surface using an elasto-plastic material model. Dominant micro-scale regular patterns were found to significantly change the contact behavior. Contact areas mainly cluster around the regular pattern. The contribution from the fractal structure is not significant. Under cyclic loading conditions, plastic deformation in the 1st loading/unloading cycle smooth the surface. The subsequent repetitive loading/unloading cycles undergo elastic contact without changing the morphology of the contacting surfaces. The work is expected to shed light on the quality of the switch surface contact as well as the optimum design of RF MEM switch surfaces.

11.67: Cyclic backbone curves for steel wide‐flange columns: A numerical study

ABSTRACTExperimental and analytical studies on the cyclic behaviour of deep, slender wide‐flange steel beam‐columns funded by the National Institute of Standards and Technology (NIST) is ongoing at the University of California at San Diego (UCSD). In parallel with full‐scale column tests, numerical simulations of columns under monotonic and cyclic loading conditions were conducted to generate a wide‐ranging database of results. A correlation study using results from the full‐scale tests was conducted to validate the numerical simulation procedure. The simulated columns covered a wide range of cross‐sectional (local) and member (global) slenderness ratios, axial force level, and yield stress. Regression analyses were conducted to construct moment‐rotation responses, ‘backbone curves’, for use in performance‐based evaluations of steel moment frames. The database is divided into three groups based on observed buckling modes. Computational expressions for the key parameters that define the backbone curves are presented.

Closest-point projection method for the extended subloading surface model

This paper presents an implicit integration scheme based on the closest-point projection method for an unconventional plasticity model, the extended subloading surface model. A cutting-plane algorithm has already been formulated for the model. However, the present paper aims to introduce an alternative closest-projection return mapping scheme for resolving the elasto-plastic problem by improving the accuracy of the similarity center variable. Numerical examples are examined for monotonic and cyclic loading conditions to validate the results against a forward Euler method. The speed and accuracy of the resolution technique are determined, showing the local and global convergence rates and the iso-error map for the numerical algorithm.

Bond behavior and interface modeling of reinforced high-performance fiber-reinforced cementitious composites

High-performance fiber-reinforced cementitious-composites (HPFRCCs) reinforced with mild steel reinforcing bars have bond strengths that are higher than ordinary concrete under monotonic loading conditions. High bond strengths in HPFRCCs have been attributed to the material toughness of HPFRCCs, which effectively restrains splitting cracks under monotonic loads. Characterization of the interface between HPFRCCs and mild reinforcement under cyclic loads remains largely unknown. The bond-slip behavior of two HPFRCC mixtures are examined under monotonic and cyclic loads in beam-end flexural specimens. Bond strength is shown to deteriorate due to cyclic load reversals after the maximum bond stress is reached, resulting in lower bond-slip toughness. Three dimensional computational simulations are conducted to investigate observed crack patterns and internal deformations at the interface of the HPFRCC and steel reinforcement. Numerical simulation results predicted splitting crack patterns observed in physical experiments, and also suggest that interface crushing occurs at the intersection of the reinforcement lugs and HPFRCC material. Further, simulated performance shows that damage to the bond interface is altered by the deformation history applied to the interface.

Validation of the repair effectiveness of clay-based grout injections by lateral load testing of an adobe model building

This study investigates the use of clay-based grout injections for the repair of adobe masonry constructions. Relevant data from the literature is reviewed, whilst the effectiveness of a laboratory-prepared clay-based grout is assessed through an experimental program. A 1:2 scaled adobe model building, previously subjected to a series of lateral loading cycles resulting in significant cracking damage, was injected with the clay-based grout and re-tested. The mix design of the aforementioned grout was based on the use of the same soil composing the earth masonry materials, hence ensuring compatibility between repairing and original materials. Although the grouting repair did not significantly alter the observed damage pattern after re-testing, it generally succeeded in preventing failure propagation through the injected crack paths. Furthermore, the injection of clay-based grout proved to be a repair technique capable of partly restoring the initial stiffness and load-bearing capacity of adobe masonry. The high strength recovery ratios recorded under the tests using static monotonic horizontal loading are particularly encouraging.