Stress Time History Research Articles

Flush Endplate Connections in Fire: Time-Dependent Behavior of Tension Bolts

Steel connections play a crucial role in maintaining the integrity and stability of steel building frames especially when exposed to fire temperatures. The behavior of flush endplate connections in fire is shown to be governed by tension bolt failure as bolts lose their strength and stiffness more rapidly at higher temperatures. As a result, the ability to predict the development of stresses in tension bolts of flush endplate connections at different stages of fire is of special importance. One of the factors influencing bolt stresses in fire is the thermal creep or time-dependent inelastic response of steel to elevated temperatures. Therefore, time- and temperature-dependent behavior of tension bolts of flush endplate connections in fire is the focus of this study. Stress-time histories in tension bolts are obtained by explicit consideration of thermal creep of steel in FE models of flush endplate connections at elevated temperatures. To better understand the effect of thermal creep on tension bolt behavior, the correlation between time-dependent rotational deformation of flush endplate connections and bolt stresses is also investigated. Further, the isochronous representation is utilized to study the rotational deformation and the tension bolt stresses under various applied moments ranging from 50% to 95% of the moment capacity and fire temperatures ranging from 450°C to 600°C with 25°C increment. Through such representation, it is indicated that the connection behavior is not only dependent on bolt strength degradation and applied moment, but also affected by the time duration of applied moments and temperatures. Also, with the inclusion of thermal creep of steel, the connection experiences higher rotation and excessive endplate deformation with stress relaxation leading to top tension bolt failure at earlier stages of fire. More specifically, for time exposure greater than or equal to 60 min, the failure temperature of the connection decreases from 600°C to around 550°C. Therefore, neglecting thermal creep of structural steel may result in an unsafe prediction of the overall response of flush endplate connections in fire.

Experimental accuracy assessment of various high-cycle fatigue criteria for a critical component with a complicated geometry and multi-input random non-proportional 3D stress components

Abstract In the present paper, a steering knuckle of a passenger car that serves as a highly critical component from the safety point of view, is considered to evaluate accuracy some of categories of the multiaxial fatigue criteria, through comparing their predictions with the experimental results. This component is subjected to the highest road- and steering-induced random and non-proportional loads that are exerted on several points of the component. The mechanical properties and fatigue strengths are determined experimentally and the fatigue life assessment tests are performed by the authors. Quantometric analyses and scanning electron microscope (SEM) have been employed to detect the failure surface of the test samples. The theoretical multiaxial fatigue life assessment of the steering knuckle has been fulfilled based on a special algorithm using the concept of cycle counting of the time history of the equivalent fatigue stresses even for fatigue criteria that have been proposed for checking the fatigue strength and not the fatigue life. Comparing the theoretical results with the experimental one reveals that the simple calibrated static-based failure criteria or linear critical-plane-type ones (e.g., von Mises, Carpinetri-Spagnoli, Findley, McDiarmid, and Dang Van) are not reliable in the very complicated situations. Furthermore, criteria using Drucker-Prager-type modifications, i.e., the regular Shariyat, Liu-Zener and especially, the Energy-based instant fatigue damage tracing proposed by Shariyat criteria (the later one, account for not only different means of the stress components but also their quite different individual frequencies and phase shifts) lead to the highest accuracies.

Probabilistic fatigue damage assessment of coastal slender bridges under coupled dynamic loads

With coupled dynamic interactions of vehicle-bridge-wind-wave (VBWW) system, fatigue damage accumulations at complicated weldments of the orthotropic steel deck (OSD) for coastal slender bridges could be critical and might affect structural safety and reliability. Due to the stochastic nature of the environmental loadings including vehicles, wind and waves, it is challenging to include uncertainties for the assessment of the fatigue damage accumulations in the bridge’s life cycle. In the present study, an efficient probabilistic fatigue damage assessment framework for coastal slender bridges is proposed with a machine learning algorithm to include the coupled stochastic dynamic loads in the VBWW system. Firstly, stochastic load models are developed based on the long-term field measurements for realistic modeling of the truck load and the correlated wind and wave load, which serve as the input for the VBWW system to extract the stress time histories at critical structural details using multi-scale finite-element analysis (FEA). After calculating the equivalent stress range and the corresponding number of cycles using the rain-flow counting method, the daily equivalent fatigue damage is obtained using the linear fatigue damage rule. To reduce the calculation cost, a machine learning algorithm is utilized for probabilistic modeling of the daily equivalent fatigue damage by integrating uniform design and support vector regression to link the multiple random inputs of environmental loadings with the single output of the stress time history. The fatigue life of critical structural details, therefore, can be obtained using the established limit-state function with a target reliability index. A prototype cable-stayed bridge in a coastal region is presented to demonstrate the effectiveness of the proposed simulation framework. Finally, the impacts of the traffic growth including the traffic volume and the gross vehicle weight on the fatigue life of three welded joints are investigated and discussed, as well.

Numerical Simulation on the Dynamic Splitting Tensile Test of reinforced concrete

The research for crack resistance was of RC was based on the split Hopkinson bar and numerical simulate software LS-DYNA3D. In the research, the difference of dynamic splitting failure modes between plane concrete and reinforced concrete were completed, and the change rule of tensile stress distribution with reinforcement ratio was studied; also the effect rule with the strain rate and the crack resistance was also discussed by the radial tensile stress time history curve of RC specimen under different loading speeds. The results shows that the reinforcement in the concrete can impede the crack extension, defer the failure time of concrete, increase the tension intensity of concrete; with strain rate of concrete increased, the crack resistance of RC increased.

Analysis of the dynamic response and fatigue reliability of a full-scale carbody of a high-speed train

For a vehicle operating under different line conditions, coupled with track irregularity and many other factors, the carbody is subjected to extremely complex random loads, and the load mainly exists in the form of an alternating load; therefore, the primary type of failure is fatigue failure. With the continuous improvement in train speed, lightweight designs of carbody structures and the application of high-strength aluminium alloy, the safety and reliability of a carbody require more attention. An investigation of the dynamic fatigue reliability of a full-scale carbody of a high-speed train under random load conditions is carried out. A dynamics model of the vehicle system has been established for acquiring the time history of forces acting on the carbody by each air spring (hereinafter referred to as ‘the load–time history’). A surrogate model (a simple model instead of a complex carbody model) of the carbody is established based on the Box–Behnken matrix design and the polynomial fitting method; then, the load–time history is transformed to the stress–time history of the points of concern, and the results are compared with the results of the transient analysis, which verify the accuracy and effectiveness of the surrogate model. Then, a stress block spectrum is obtained by rain flow counting, and the stress probability distribution is determined. Combined with the probability distribution of fatigue strength, a dynamic stress–strength interference model (the area of interference between strength and stress in the model changes over time) is established. The failure rate and dynamic reliability of the points of concern for two cases are analysed: without considering the strength degradation and considering the strength degradation. The results show that without considering the strength degradation during service, with increased service mileage, the fatigue strength reliability of the points of concern decreases continuously, and the corresponding failure rate of the points of concern decreases with time and reaches a steady value, which has the characteristics of the first two stages of the bathtub curve. By considering the strength degradation during service, the reliability of the points of concern decreases gradually, and the corresponding failure rate of the points of concern decreases and then increases, with all the features of the bathtub curve. In addition, compared with the base metal region, the fatigue resistance of the welded structure decreases due to welding. Under the same service conditions, the reliability of the welded region is relatively low, and fatigue failure is more likely to occur.

Fatigue life prediction of engaging spur gears using power density

The high cycle fatigue performance of an input spur gear pair found in the gearbox of a 4LZ-2 combined harvester with a maximum walking power of 15 kW is investigated. A three-dimensional finite element model of the two engaging spur gears is developed to estimate the fatigue life of the pinion gear subject to bending induced crack initiation and propagation. The critical point of the pinion gear is obtained along with the associated bending stress-time history. The novel concept of power density is applied to the finite element result to correlate fatigue crack initiation and subsequent crack growth with the number of loading cycles undergone. After the location of crack initiation is identified, fatigue crack propagation is modelled using linear elastic fracture mechanics. The estimated fatigue life of the pinion gear is 886 h. A fatigue test rig is employed to physically demonstrate the feasibility of the power density concept for predicting gear fatigue life. It is shown that the power density concept is preferred over the Miner rule for higher accuracy in fatigue life prediction.

Simulation of Structure Dynamic Stress under Multi-load Condition in Resonance State

Some metro vehicle lifeguard structure cracking emerged during operation, and the reason is due to resonance. In order to simulate the dynamic stress accurately in resonance state, the formula for calculating the dynamic stress under multi-load condition was deduced based on structural dynamics mechanics. During the dynamic stress simulation, firstly, the frequency response function (FRF) of each external load was calculated, which including the phase information. Then, the method was based on Fast Fourier Transform (FFT) to get the frequency domain with real and imaginary part of each external load rather than power spectrum density (PSD) calculation, avoiding loss of the phase information due to PSD method. Finally, the dynamic stress frequency domain data could be calculated by FFT results and FRFs. Based on above, the dynamic stress time history could be acquired by Inverse FFT (IFFT) of stress frequency domain data, and the stress simulation method was verified by the line test result. Compared with the conventional stress PSD calculation method, the method in this paper can retain the phase information of the each external load. Meanwhile, the conventional stress simulation method based on PSD could not get satisfactory result.

Evaluation of fatigue damage with an energy criterion of simple implementation

Many theoretical methods for multiaxial fatigue life prediction are present in literature, most of them based on their effectiveness on knowledge of the entire stress time history. This represents the great applicative limit. The incapacity to study real situations, not only deterministic one, let the authors to develop a simple and rigorous criterion, which helps the designer who works in this area. The criterion is presented focusing the attention on the basic premise, highlighting its applicability, its practicality and its computational power. To do that, the Authors take into account the deterministic or random character of the individual constraint components and their degree of correlation. In order to verify the method, simulations of multiaxial loads conditions, developed in the time domain, will be carried out with various correlation levels between the stress components on which the method will be applied.

Design, service and testing grounds stress spectra and their using to fatigue life assessment of bus bodyworks

In the development of a road vehicle such as a bus, the input data for the assessment of the fatigue life of the body and other mechanical parts of the vehicle are gradually refined. In the initial phase of the development of a new vehicle, so-called design stress spectra are used. It is necessary to estimate the design spectrum parameters correctly. At the vehicle's prototype testing phase, the so-called service stress spectra can be evaluated. It is essential to determine the characteristic operating modes of the vehicle and to record representative stress-time histories of the critical sections of the construction nodes and vehicle components. Accelerated driving test of fatigue life can be performed on special test routes. The acceleration of such a fatigue test is dependent on the test track composition. The paper generally describes the methodology of such a process and demonstrates it using unique real-time data acquired during the development of a bus.

High Rate Response and Dynamic Failure of Aluminosilicate Glass under Compression Loading

The mechanical behavior of un-strengthened aluminosilicate (ALS) glass is studied experimentally by using modified Split Hopkinson pressure bar and electronic universal testing machine. The compression tests on glass specimens are performed at strain-rates in the range of 10− 4 to 102s−1. The compression tests data revealed that ALS glass is strain-rate sensitive vis-à-vis the compressive strength of the glass. In dynamic compression tests, failure process of glass is investigated using a high-speed camera and the failure process in ALS glass is explicated with the associated stress-time history. The initiation of crack, development, and glass debris are discussed to explain the failure process of glass specimens. Test results showed that the axial splitting lead to final rupture of the glass. From both static and dynamic compression tests, the compressive strength, failure strain and energy absorption results for ALS glass specimens are also compared.

Three-dimensional thermoviscoelastic analysis of a FGM cylindrical panel using state space differential quadrature method

ABSTRACTMechanical behavior of a viscoelastic cylindrical panel with various edge boundary conditions, made up of functionally graded material (FGM) and subjected to thermal or mechanical load is investigated. For cases of simply supported boundary conditions, analytical solution is presented through Fourier series expansion along the axial and circumferential coordinates as well as state space method along the radial coordinate. For nonsimply supported conditions, semi-analytical solution is performed using differential quadrature method instead of Fourier series solution. Governing differential equations are transformed to Laplace transform domain and using inverse Laplace transform, obtained solutions are converted to time domain. In the present work, relaxation modulus of FGM is supposed to be according to the Prony series with power law variations along the radial direction. Numerical comparison was made with the available published results to assess the validity of present technique. Effect of relaxation time constant, thickness to mid-radius ratio, edges boundary condition and outer surface temperature on stress and displacement fields are discussed. Besides, time history of stresses for different relaxation time constant and for various boundary conditions is presented.

Fatigue damage detection and prediction of fatigue life on a cantilever beam

Purpose Fatigue failure is an important criterion to be considered in the design of structures and mechanical components. Catastrophic failure of structures in service conditions can be avoided using adequate techniques to detect and localize fatigue damage. Modal analysis is a tool used in mechanical and structural engineering to estimate dynamic properties and also to monitor the health of structures. If modal analysis is applied periodically to a structure, fatigue damage can be detected and localized and the fatigue life can be extended by means of suitable reinforcement and repairing. The paper aims to discuss these issues. Design/methodology/approach The experimental results corresponding to the fatigue tests carried out on a steel S-275 cantilever beam are presented. Operational modal analysis was applied periodically to the beam in order to study the variation of modal parameters during the tests and the stresses were estimated combining a numerical model and the acceleration modal coordinates measured at discrete points of the structure. The experimental results are compared with those predicted applying the S-N model of Eurocode 3. Findings A methodology that combines a finite element model and the experimental responses of a structure has been applied to estimate the stress time histories of a cantilever beam clamped to a foundation through a steel plate. The estimated stresses have been used to predict the fatigue damage according to the Eurocode 3. Due to the fact that no information of the scatter is provided by this code (EC3), only the number of cycles corresponding to a probability of failure of 5 percent can be predicted. Originality/value The proposed methodology can be applied to real structures in order to know the accumulated fatigue damage in real time.

Domain-boundary element method for elastodynamics of functionally graded Timoshenko beams

A new domain-boundary element method is developed for elastodynamic analysis of functionally graded Timoshenko beams. Three governing partial differential equations of motion are derived by considering through-the-thickness variations of the physical properties. Weighted-residual forms are imposed utilizing the static fundamental solutions. These forms are then reduced to three integral equations containing domain integrals with time derivatives of unknown functions. Through domain discretization and shape function approximation, integral equations are converted to a system of ordinary differential equations in time. Forced dynamic response is revealed by solving the system of equations via Houbolt method. Comparison of dynamic responses generated for homogeneous beams to those calculated through an analytical solution and finite difference method verify the developed procedures. Further parametric analyses are performed for functionally graded Timoshenko beams under step, harmonic, and impulsive loadings. The numerical results presented illustrate the influence of material inhomogeneity on time histories of deflection and stress. Domain-boundary element method is demonstrated to be an effective technique for elastodynamic analysis of functionally graded structures.

DTH 천공기의 드릴리그와 붐에 대한 정적/동적 구조해석

This paper presents the design and structural analysis for the drill rig and boom of a down-the-hole (DTH) drilling machine. The purpose of the structural analyses is to design the drill rig and boom to satisfy the structure safety criterion. The static analysis was performed by analyzing the stress distributions in the structure parts. The stress distributions are computed by applying the dead weights to the parts for the various work positions. On the other hand, the dynamic analysis was carried out by investigating the time histories of stress at stress-concentrating points. The time histories are obtained by considering the impact force and rotating force. The static/dynamic structural analysis for the drill rig and boom shows that the proposed design satisfies the target safety criterion.

Added mass effect for tip-over analysis of dry cask composite structures at two different scales

Safety of dry-cask storage structures, containing spent nuclear fuel, has always been an important concern for the nuclear industry. Detailed investigations of the mechanical response of these important composite structures due to hypothetical accident conditions have been the subject of many studies. In this paper, a tip-over induced impact of a dry cask is numerically analyzed at two different dimensional scales, i.e., a full-scale “prototype” and a 1/3-scale “model cask”. The latter is considered to study the accuracy of similitude laws because most experiments are done at the reduced scale. The added mass technique is applied to the model cask using the dynamic similitude concept in order to represent the behavior of the prototype cask. The effects of this added mass are also studied in terms of damage parameters, time histories of strains, stresses and accelerations to compare these two models. The results demonstrate that the added mass is able to predict the behavior of the model cask compared to that of the full-scale prototype.

A NUMERICAL STUDY OF WAVE-CURRENT INTERACTION IN THE BOTTOM BOUNDARY LAYER

In the present work, a numerical wave-current flume has been developed, based on a standard k-ε model. The numerical flume was 12.86m in length, with a numerical beach at one end of the flume. The Volume of Fluid (VOF) method was used to capture the free surface in the flume. The velocity profile obtained at the test section from the numerical simulation has then been compared with experimental data and good agreement found. Periodic velocities in the bottom boundary layer have been obtained which agree well with the experimental data. The model provides an insight to the changes in bed shear stress time histories that characterise wave current interaction.

Fatigue assessment of an existing steel bridge by finite element modelling and field measurements

The evaluation of fatigue life of structural details in metallic bridges is a major challenge for bridge engineers. A reliable and cost-effective approach is essential to ensure appropriate maintenance and management of these structures. Typically, local stresses predicted by a finite element model of the bridge are employed to assess the fatigue life of fatigue-prone details. This paper illustrates an approach for fatigue assessment based on measured data for a connection in an old bascule steel bridge located in Exeter (UK). A finite element model is first developed from the design information. The finite element model of the bridge is calibrated using measured responses from an ambient vibration test. The stress time histories are calculated through dynamic analysis of the updated finite element model. Stress cycles are computed through the rainflow counting algorithm, and the fatigue prone details are evaluated using the standard SN curves approach and the Miner’s rule. Results show that the proposed approach can estimate the fatigue damage of a fatigue prone detail in a structure using measured strain data.

Embedded piezoelectric lead-zirconate-titanate-based dynamic internal normal stress sensor for concrete under impact

The direct stress measurement is critical for the constitutive law investigation of concrete materials and dynamic behavior study of concrete structures under strong dynamic loadings where the strain-rate effect and the plastic behavior should be considered. In this article, an embedded dynamic internal normal stress sensor for concrete by employing piezoelectric lead-zirconate-titanate (PZT) patch as a sensing element is developed. After being calibrated under sinusoidal loadings with different frequencies, periodical square loadings, and random loadings, the developed dynamic internal normal stress sensor is further calibrated with a unique self-developed free-falling drop hammer with different impact velocities. The sensitivity of the developed normal stress sensor is determined accordingly. Finally, the developed sensors are employed to monitor the dynamic normal stress time history at different locations of concrete cylinder specimens under impacts with different velocities using a large-scale drop hammer test facility. The dynamic increase factors of concrete strength under impact are determined and compared with the values determined by the Comité Euro-International du Béton code. The experimental results indicate that the PZT-based embedded dynamic internal normal stress sensor provides a novel way for the direct dynamic normal stress measurement of concrete specimens under impact loadings.

Simulation of cell-substrate traction force dynamics in response to soluble factors

Finite element (FE) simulations of contractile responses of vascular muscular thin films (vMTFs) and endothelial cells resting on an array of microposts under stimulation of soluble factors were conducted in comparison with experimental measurements reported in the literature. Two types of constitutive models were employed in the simulations, i.e. smooth muscle cell type and non-smooth muscle cell type. The time histories of the effects of soluble factors were obtained via calibration against experimental measurements of contractile responses of tissues or cells. The numerical results for vMTFs with micropatterned tissues suggest that the radius of curvature of vMTFs under stimulation of soluble factors is sensitive to width of the micropatterned tissue, i.e. the radius of curvature increases as the tissue width decreases. However, as the tissue response is essentially isometric, the time history of the maximum principal stress of the micropatterned tissues is not sensitive to tissue width. Good agreement has been achieved for predictions of the vasoconstrictor endothelin-1-induced contraction stress between the FE numerical simulation and the experiment-based approach of Alford (Integr Biol 3:1063-1070, 2011) for the vMTFs with 40, 60, 80 and 100 [Formula: see text] width patterns. This may suggest the contraction stress is weakly sensitive to the tissue width for these patterns. However, for 20 [Formula: see text] width tissue patterning, the numerical simulation result for contraction stress is less than the average value of experimental measurements, which may suggest the thinner and more elongated spindle-like cells within the 20 [Formula: see text] width tissue patterning have higher contractile output. The constitutive model for non-smooth muscle cells was used to simulate the contractile response of the endothelial cells. The substrate was treated as an effective continuum. For agonists such as lysophosphatidic acid and vascular endothelial growth factor, the deformation of the cell diminishes from edge to centre and the central part of the cell is essentially under isometric state. Numerical studies demonstrated the scenarios that cell polarity can be triggered via manipulation of the effective stiffness and Possion's ratio of the substrate.

Analysis of Vehicle-Force-Induced Dynamic Pore Pressure in Saturated Pavement With LSPM Drainage Base

Abstract Dynamic pore pressure caused by moving-vehicle forces may cause damage in asphalt pavement. However, few field data of dynamic pore pressure are available. This research aimed to study the time histories of dynamic stress and dynamic pore pressure in the drainage base of large stone porous asphalt mixes (LSPM) under moving-vehicle forces. To this end, heat-resistant dynamic stress and pore-pressure sensors were developed and used to measure the dynamic stresses and pore pressures in the field. A numerical fluid-solid coupling simulation method was used to analyze the response of pavement under moving wheel forces. Numerical simulation results matched well with in situ test data. The time histories of dynamic pore pressure in the pavement are quantitatively analyzed, and the hydraulic mechanism of moisture-induced damage is verified. This study provides a theoretical guide for pavement design.