Static Loading Experiments Research Articles

Optimal Sensor Placement Based on Eigenvalues Analysis for Sensing Deformation of Wing Frame Using iFEM.

For real time monitoring of the wing state, in this paper, the inverse Finite Element Method (iFEM) is applied, which describes the displacement field of beam according to the Timoshenko theory, to sense the wing frame deformation. In order to maintain the accuracy and stability of frame deformation sensing with iFEM, an optimal placement model of strain sensors based on eigenvalue analysis is constructed. Through the model solution with the Particle Swarm Optimization (PSO) algorithm, two different optimal placement schemes of sensors are obtained. Finally, a simulation is performed on a simple cantilever beam and a static load experiment is conducted on an aluminum alloy wing frame. The results demonstrate that the iFEM is able to accurately sense the deformation of the wing frame, when the two optimal placement schemes of sensors are used.

Failure mechanisms of CFRP-wrapped protective concrete arches under static and blast loadings: Experimental research

In this research, failure mechanisms of carbon fiber reinforced polymer (CFRP) wrapped protective arches under static and blast loadings were investigated through experiments. Adopting bonding and partially-wrapping scheme, the plain concrete (PLC) arch is strengthened and its load carrying ability achieves the level of steel bar reinforced concrete (RC) arch in the static loading experiment. Adopting bonding and fully-wrapping scheme, it’s akin to apply hollow CFRP tubular arch to reinforce plain PLC arches. Load carrying capacity of the CFRP composite arch achieves twice as much as that of the RC arch and the composite arch fails in a shear mode. Subjected to explosive loading, anti-blast ability of the CFRP tubular concrete arch is much better than the PLC arch. Critical scaled distance to prevent the arch from dynamic broken is considerably reduced. According to the research, it is confirmed that using the composite technique an efficient composite protective arch structure can be constructed and steel reinforcements can be entirely replaced by CFRP in some cases, such as coastal engineering and anti-blast structures.

Design, Modeling, and Validation of a Soft Magnetic 3-D Force Sensor

Recent advances in robotics promise a future where robots co-exist and collaborate with humans in unstructured environments, which will require frequent physical interactions where accurate tactile information will be crucial for performance and safety. This article describes the design, fabrication, modeling, and experimental validation of a soft-bodied tactile sensor that accurately measures the complete 3-D force vector for both normal and shear loading conditions. Our research considers the detection of changes in the magnetic field vector due to the motion of a miniature magnet in a soft substrate to measure normal and shear forces with high accuracy and bandwidth. The proposed sensor is a pyramid-shaped tactile unit with a tri-axis Hall element and a magnet embedded in a silicone rubber substrate. The non-linear mapping between the 3-D force vector and the Hall effect voltages is characterized by training a neural network. We validate the proposed soft force sensor over static and dynamic loading experiments and obtain a mean absolute error below 11.7 mN or 2.2% of the force range. These results were obtained for a soft force sensor prototype and loading conditions not included in the training process, indicating strong generalization of the model. To demonstrate its utility, the proposed sensor is used in a force-controlled pick-and-place experiment as a proof-of-concept case study.

Mechanical property analysis of disc spring

Based on the finite element method, numerical simulation models of a standard disc spring were built and force–displacement curves were obtained under different displacement loads. Then the static loading experiments were conducted by the tensile experimenting machine. The computation model was validated by comparison of the model predictions with the experimental results. The results of the numerical simulation model were in good agreement with the experimental data. Based on the finite element method, models of grooved disc springs were established. The force–displacement and stiffness–displacement curves for the disc springs with different groove configurations were obtained. And the results were verified by the experiment data. The effects of the distribution and number of the grooves on the load variation, the stiffness change, the negative stiffness region in the force–displacement curve were analyzed. The research has good reference value for the design of disc spring with negative stiffness and the application of negative stiffness part in reducing vibration and vibration isolation device.

Load Distribution Calculation of a four-Point-Contact Slewing Bearing and its Experimental Verification

Analysis of the load distribution along raceways is fundamental for assessing dynamic and static capacity of the slewing bearings. In the literature, several finite element (FE) models have been proposed to estimate the load distribution and the deformation of slewing bearing. Although FE simulations are a useful tool for designers, there are a few experimental studies assessing accuracy and reliability of computations. In this paper, a FE model for a single-row four-point-contact slewing bearing is built in ABAQUS software. The key to the method is to simulate the balls under compression by traction-only nonlinear springs. Subsequently, the static loading experiment is designed: strain gauges are mounted on the inside circumference of the inner ring to obtain load distribution. The comparison between numerical and experimental results is discussed in detail. Remarkably, FE results are consistent with experimental data.

Deformation monitoring of typical composite structures based on terrestrial laser scanning technology

Terrestrial laser scanning (TLS) technology plays an important role in the field of deformation monitoring nowadays, and a lot of the architectures are arched composite structures, which are required to be further understood for their mechanical and physical properties. Only a theoretical numerical analysis is sometimes difficult and defective to achieve, due to varying loads and other factors influencing the stability and reliability of such structures. Therefore, measurements can improve the theoretical analysis in several ways. One of the most important issues is the deformation analysis within load experiments.This paper focuses on the presentation of new possibilities for surface-based measurement techniques and their applicability in the deformation analysis of arched structures. The goal of this paper is to investigate the difference of load-displacement relationships between arched and beam structures though a static load experiment based on high accuracy TLS measurement techniques and the surface analysis method. In this paper, we try to reveal the influencing mechanism of ‘prestressing-like’ force and interpret why arched structures can withstand a surprisingly greater load than beam structures under the same conditions.

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...

Structural bionic design for a machine tool column based on leaf veins

Some biological structures, such as leaf veins, bamboo and animal bones, have excellent mechanical properties after millions of years evolution. By studying the distribution characteristics of biological structures, the performances of mechanical components can be improved using structural bionic design method. In this paper, the internal stiffening ribs of a machine tool column are rearranged based on the structure of leaf veins, and a bionic column is designed. Static and modal analysis of the conventional and bionic column is conducted to investigate the static and dynamic performances by finite element method. Then, static loading experiment and modal test are carried out for further verification. The simulation results have good agreement with the experiment results. Compared with the conventional column, the maximum deformation of the bionic column in experiment is reduced by 24.69%, and the first six-order natural frequencies of bionic column are increased by 48.39%, 12.98%, 10.70%, 5.11%, 3.07%, and 8.44%, respectively.

Influence of toe load on the fatigue resistance of elastic rail clips

As a critical component of the fastening system, the elastic rail clip maintains the rail in the vertical, lateral, and longitudinal positions using its specified toe load. In this study, the influence of toe load on the deformation and fatigue resistance of the clip was studied. Finite element analysis, static load experiments, and fatigue experiments were performed to evaluate the deformation and fatigue resistance of the clip. With the contribution of the lateral wheel load, the deformation range of the outer clip was higher than that of the inner clip. Therefore, the cyclic deformation of the outer clip was used for the fatigue experiment. The toe load had no influence on the fatigue resistance of the clip under normal wheel load, i.e. the clips under high, normal, and low toe loads were run-out at 5 × 106 cycles. However, with the contribution of impact on the wheel load, the fatigue lives were reduced to 5468 cycles and 16,839 cycles for the clips under high and normal toe loads, respectively. In the case of low toe load, the clip under the contribution of impact could withstand more than 5 × 106 cycles. Accordingly, the reduction of toe load may enhance the fatigue resistance of the clip under impact.

A New Type of Shock Isolator and Its Experimental Verification of Quasi-Zero-Stiffness Characteristic

Shock is a kind of phenomenon existing extensively in practical engineering projects, which is harmful to structural security. The main method to reduce the dynamic coupling between the shock excitation source and the object being isolated is implemented by setting isolators. Aimed at the problem that the conventional isolators cannot provide large-displacement and efficient isolation ability, a new type of shock isolator is presented in this paper, which can be simplified as a nondestructive expansion mechanism. The large-displacement and quasi-zero-stiffness characteristics of the isolator are verified through the static and dynamic loading experiments. Thus, with the favorable stiffness characteristics, this type of shock isolator would have broad application prospects in the relevant fields.

Experimental study on flexural performance of partially precast steel reinforced concrete beams

An innovative partially precast steel reinforced concrete beam, which is abbreviated here as PPSRC beam, is presented in this paper. An improved type, an innovative hollow-core PPSRC beam, which is abbreviated HPSRC, is also introduced here. These two types of beams both have two parts, the precast outer-part and the cast-in-place inner-part. To investigate the flexural performances of the PPSRC beam and the HPSRC beam, static loading experiments were carried out on seven specimens, including three PPSRC T-beam specimens and three HPSRC T-beam specimens together with a cast-in-place SRC control T-beam specimen. In the tests, the flexural performances of the PPSRC beams and the HPSRC beams were emphasized, and the effect of the compressive strength of concrete in the inner-part was also taken into account. On the basis of the experiments, the failure mode, strain development and ultimate bearing capacity were thoroughly examined. The flexural failure mechanisms of the PPSRC beams and the HPSRC beams were clearly revealed. From comparison of the test results, the flexural performance of the HPSRC beam was similar to that of the PPSRC beam and was even comparable to that of the cast-in-place SRC beam. The calculation method for flexural capacity was also presented in this paper. The analysis of mechanical behavior and the design method can be used for the design of these innovative composite beams and provide a significant foundation for further research.

Study of the design and mechanical performance of a GFRP-concrete composite deck

A GFRP-concrete composite bridge deck is presented in this paper. This composite deck is composed of concrete and a GFRP plate and is connected by GFRP perfobond (PBL) shear connectors with penetrating GFRP rebar. There are many outstanding advantages in mechanical behavior, corrosion resistance and durability of this composite deck over conventional reinforced concrete decks. To analyze the shear and flexural performance of this GFRP-concrete composite deck, a static loading experiment was carried out on seven specimens. The failure modes, strain development and ultimate bearing capacity were thoroughly examined. Based on elastic theory and strain-based theory, calculation methods for shear and flexural capacity were put forward and revised. The comparison of tested and theoretical capacity results showed that the proposed methods could effectively predict both the flexural and shear capacity of this composite deck. The ACI 440 methods were relatively conservative in predicting flexural capacity and excessively conservative in predicting shear capacity of this composite deck. The analysis of mechanical behavior and the design method can be used for the design of this composite deck and provides a significant foundation for further research.

Terrestrial Laser Scanning-Based Deformation Analysis for Arch and Beam Structures

Nowadays, with the assistance of the high accuracy terrestrial laser scanning (TLS) measurement techniques, the mechanics analysis of structures could be better understood. This paper has a comparative analysis of arch and beam structures in terms of deformation behavior in loading experiments. The goal of this paper is to discover the potential value of the different structures in the architecture through the investigation of the anti-load capacity of the arch and beam structures. This paper is focused on the comparison of load-displacement relation between arch and beam with static load experiment, which is based on TLS techniques and surface analysis method. The innovation is that we try to reveal the partial area changing rules named “partial area analysis,” which is a new method to investigate the deformation behavior of structure. It is exposed that both arch and beam structures in the loading progress would suffer three stages, which are steady, developing, and fracture. Furthermore, considering the effect of pre-stress, steady stage would last longer, and developing and fracture stages would be hysteretic.

Computational and experimental investigation into mechanical performances of Poly-L-Lactide Acid (PLLA) coronary stents

Poly-L-lactide Acid (PLLA), as a credible biodegradable polymer-based material, can provide a promising amount of degradation time for vessel remodeling. Served as a sort of reliable intravascular implants, PLLA stents are expected to provide sufficient scaffolding to the target arteries without generating too much recoil after deployment. Besides, the stress and strain distribution should be as homogeneous as possible, and the stent conformability in fitting to the nature curvature of the vessels needs to be guaranteed. In the present study, mechanical performances of a stent made of PLLA material were investigated based on 3-D finite element method (FEM) and experiment verification. Simulations contained several deformation steps: crimping, spring-back after crimping, expanding and spring-back after expanding. The stent’s deformation and stress/strain distributions were analyzed. Several indexes including the radial recoil ratio after crimping and expanding to different sizes, the radial properties including radial strength, the radial stiffness and the collapse pressure were established. In vitro static loading experiments of the stent were conducted as the verification of the FEM results, and a good agreement between them was obtained. Moreover, simulation of three-point bending was performed to assess the bending flexibility of the stent, and bending stiffness was defined as a measurement of structure resistance to the bending deformation.

A bridge safety monitoring system for prestressed composite box-girder bridges with corrugated steel webs based on in-situ loading experiments and a long-term monitoring database

In order to reduce the self-weight of Highway No. 4 in the Taichung living circle in Taiwan, a corrugated steel web, with a span of 145m, is used to replace the conventional concrete web. To appraise the structural safety and operating conditions of a prestressed composite box-girder bridge with a corrugated steel web, which is the first bridge of its kind in Taiwan, a bridge monitoring system is developed based on in-situ experiments, numerical modeling, and long-term monitoring. In order to determine the initial static and dynamic behaviors of a real bridge, a series of experiments are first carried out on a newly-constructed bridge. Before entering service, a bridge is subjected to forced vibration experiments and static loading experiments to establish its initial condition. In this study, a numerical model of the bridge is constructed based on the finite element method. The results of the structural analysis are compared with experimental data, and the two sets of results are found to show good agreement. Moreover, thermometers, strain gages, displacement gages, and inclinometers are installed on the bridge to measure changes in the physical quantities, and the monitored temperature gradient profile over a year is fed back to the numerical model for further analysis. Results have indicated that the in-situ linear variable differential transformer (LVDT) and inclinometer monitoring data can be effectively simulated by the numerical model. Finally, based on the material properties, numerical model, and long-term monitoring data from inclinometers, the safety threshold of the bridge is determined to provide a useful reference for bridge management agencies. Prediction of the extreme inclination angles by the Generalized Extreme Value Distribution (GEVD) method for the 50-year life cycle of the monitored bridge also falls within the envelopes of the warning and critical thresholds, which support the long-term safety of bridges.

Full-Range S-N Fatigue-Life Evaluation Method for Welded Bridge Structures Considering Hot-Spot and Welding Residual Stress

AbstractFatigue cracking is crucial issue for welded steel bridges that endure repeated vehicle loads. With typical fatigue-life evaluation methods, it is difficult to consider the influence of low stress amplitude. Based on existing full-range S-N curves and their formulas for base metal, a unified fatigue-life evaluation method is recommended for welded joints. The basis for construction of full-range S-N curves is to obtain the welding residual stress and stress concentration factor. In this paper, rib-to-deck welded joints are introduced as examples to demonstrate the detailed steps of a fatigue-life evaluation procedure. From the analysis of welding residual stress, it can be concluded that residual stress is influenced by the geometric dimensions of the composite members. With an increase in the geometric dimensions, the level of residual stress is increased. In addition, static-load experiments were conducted to obtain the stress concentration factor. A hot-spot full-range S-N curve was then obtain...

Static and dynamic characteristic analysis of high-speed press bed based on virtual simulation

This paper establishes a three-dimensional solid model of J76-125 Straight Side High-speed Double-crack Precision Press using CATIA, and then the model is imported into an ANSYS environment to form the static and dynamic finite element simulation model. Based on the finite element analysis method, the static stress, deformation, vibration mode and transient response of the press bed are developed under preload conditions, as well as under the combination of the preload and nominal pressure conditions. Besides, the static loading experiment, the mode experiment and the pile-driving experiment are conducted to revise the simulation model. Finally, the simulation model and analysis procedure are verified through the comparison of the experiment results and the simulation ones.

Fatigue-Life Evaluation of a High-Speed Railway Bridge with an Orthotropic Steel Deck Integrating Multiple Factors

AbstractThe driving security of trains at high speeds is among the pivotal issues significantly affected by the smoothness of rail lines. For high-speed railway steel bridges, the fatigue cracking of typical positions under the rail lines will reduce the stiffness of the deck plate, inducing the smoothing of the rail lines. In this paper, a new theoretical approach is proposed that integrates the fatigue assessment of a typical welded joint for high-speed railway steel bridges in service. Based on the strain history data recorded by a structural health monitoring system, the theoretical approach includes various factors, including stress concentration, environmental corrosion, and train flow. Upon application in an actual high-speed railway bridge with an orthotropic steel deck, the approach was used to conduct determinative and reliable fatigue-life evaluation of the bridge. A static-load experiment was conducted to obtain the stress distribution around the weld and the difference in stress between the p...

In vitro stress effect on degradation and drug release behaviors of basic fibroblast growth factor--poly(lactic-co-glycolic-acid) microsphere.

ObjectiveTo study the degradation and basic fibroblast growth factor (bFGF) release activity of bFGF – poly(lactic-co-glycolic-acid) microsphere (bFGF-PLGA MS) under stress in vitro, including the static pressure and shearing force-simulating mechanical environment of the joint cavity.MethodFirst, bFGF-PLGA MSs were created. Meanwhile, two self-made experimental instruments (static pressure and shearing force loading instruments) were initially explored to provide stress-simulating mechanical environment of the joint cavity. Then, bFGF-PLGA MSs were loaded into the two instruments respectively, to study microsphere degradation and drug release experiments. In the static pressure loading experiment, normal atmospheric pressure loading (approximately 0.1 MPa), 0.35 MPa, and 4.0 MPa pressure loading and shaking flask oscillation groups were designed to study bFGF-PLGA MS degradation and bFGF release. In the shearing force loading experiment, a pulsating pump was used to give the experimental group an output of 1,000 mL/min and the control group an output of 10 mL/min to carry out bFGF-PLGA MS degradation and drug release experiments. Changes of bFGF-PLGA MSs, including microsphere morphology, quality, weight-average molecular weight of polymer, and microsphere degradation and bFGF release, were analyzed respectively.ResultsIn the static pressure loading experiment, bFGF-PLGA MSs at different pressure were stable initially. The trend of molecular weight change, quality loss, and bFGF release was consistent. Meanwhile, microsphere degradation and bFGF release rates in the 4.0 MPa pressure loading group were faster than those in the normal and 0.35 MPa pressure loading groups. It was the fastest in the shaking flask group, showing a statistically significant difference (P<0.0001). In the shearing force loading experiment, there were no distinctive differences in the rates of microsphere degradation and bFGF release between experimental and control group. Meanwhile, microsphere degradation and bFGF release rates by shaking flask oscillation were obviously faster than those by shearing force only (P<0.0001).ConclusionThere are significant effects on bFGF-PLGA MS degradation and bFGF release due to the interaction between extraction stress and time. Static pressure has a conspicuous influence on bFGF-PLGA MS degradation and release, especially at a pressure of 4.0 MPa. The shearing force has a slight effect on bFGF-PLGA MS degradation and drug release. On the contrary, shaking flask oscillation has a significantly distinctive effect.

Evaluation of Seismic Resistance Capacity on Supporting Structure of Spherical Tank using Static Load Experiment

Evaluation of Seismic Resistance Capacity on Supporting Structure of Spherical Tank using Static Load Experiment