Force-deflection Curves Research Articles

Experimental study on shear performance of PET FRP-strengthened RC beams without stirrups

The shear behavior of simply supported RC beams strengthened with polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) was studied in this paper. The test variables include strengthening schemes (i.e., U-wrapping and full-wrapping) and FRP reinforcement ratios. A comprehensive and meticulous investigation was conducted on the failure mode of RC beams, shear force-deflection curves, the development process of shear cracks, the evolution of FRP strain, and the interaction between FRP and concrete. The shear capacity and deformation were increased by 42.5–123.2% and −16.34–96.89% using the fully wrapped scheme, respectively. The improvement in shear capacity was 42.5–72.55% when the U-wrapped scheme was adopted. The PET FRP fully wrapped beams exhibited a type of ductile shear failure. The strain of PET FRP in the fully wrapped specimen exceeded 4% without fracture, ensuring the deformation capacity after the peak load. The shear deformation caused the increase in post-peak mid-span deflection. The U-wrapped specimens showed debonding failure, with the debonding strain of PET FRP being more than that of conventional FRP. Finally, six design guidelines for PET FRP shear contribution were evaluated for both U-wrapped and fully wrapped schemes.

Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

Modeling the initiation and propagation of complex networks of cracks in reinforced concrete plates

The present paper proposes a new finite element formulation for the analysis of RC slabs, accounting for concrete cracking and reinforcement yielding. The proposed formulation, developed within the framework of Lumped Damage Mechanics, considers that all inelastic effects are localized in lines and relates all numerical parameters to the mechanical properties of the slab. The proposed variational approach is presented as a Nash noncooperative equilibrium point. It is verified, numerically, that the proposed FE leads to mesh-independent results. Numerical simulations of some experimental tests are also presented. The results in terms of collapse mechanism, cracking network, and force-deflection curves showed that the model has significant accuracy, even for non-symmetric free clamped and simple supported boundary conditions. It is also shown, through the confrontation with experimental results, that the model correctly characterizes the initiation and development of complex networks of cracks.

An improved analysis of small punch deformation for evaluating tensile properties

Small punch (SP) method is a promising technique for evaluating tensile properties using small volumes of test material, yet its applicability is bound by large errors in estimation of tensile yield strength (YS) using the yield force (FY) determined by the existing two tangent, offset or bilinear function fitting methods. In this study, a yield force (FY) based on the occurrence of yielding across the specimen thickness is identified through finite element analysis and a methodology is formulated for determination of FY from experimental data, supported with acoustic emission (AE) technique. The YS-FY correlation for various structural steels, Inconel and Aluminium exhibit excellent linearity and standard errors within ±7 %. Based on the onset of plastic instability in SP deformation at an inflection point (Fs, us) of force-deflection curve, the specimen deflection us is shown to correlate with tensile uniform strain better than parameter um (deflection at peak load). The tensile properties of neutron irradiated SS 316 evaluated from SP tests using the methodologies and SP-tensile correlations formulated in this work, are found to be within 6–8 % of the uniaxial tensile test results.

Author Correction: Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

Author Correction: Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

Evaluating the tensile properties of high-strength stainless steels using small punch testing.

Accurately measuring the mechanical properties of high-strength stainless steels is of great significance for ensuring structural safety, predicting long-term performance and optimizing design. However, the standardized tensile test specimens used to obtain strength properties must be fabricated from bulk materials from an in-service structure or component, result in the loss of structural integrity or a reduction in remaining service life. Small punch tests require only miniscule material samples and are widely used to estimate in-service component material characteristics. This study performed small punch tests on three high-strength stainless steels-X17CrNi15-2, 15-5PH, and PH13-8Mo-to obtain the correlations between the small punch tests and the uniaxial tensile test results for each material. The estimated yield stresses obtained from the small punch tests were distributed within a factor of 1.5 on both sides of the unity line when compared with those obtained from the uniaxial tensile tests; the ultimate strength values estimated from the small punch tests correlated quite well with those obtained from the uniaxial tensile tests. An iterative finite element analysis was subsequently established to simulate the small punch tests and thereby obtain the coefficients for a Ludwik power law correlation representing the true stress-strain properties. The finite element predicted force-deflection curves agreed well with the small punch test results, which were also compared with the predictions obtained from empirical equations proposed in previous studies. Finally, the fracture mechanisms of the small punch test specimens were characterized through scanning electron microscopy, indicating that the dimple fracture mechanism dominated the failure mode. The results of this study are expected to inform the application of small punch test to evaluate in-service high-strength stainless steel materials.

Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

Young's Modulus Characterization of Nano‐Level Silicon Nanomembrane

Silicon nanomembrane (SiNM) has drawn great attention for the application in nanoelectrical devices as it shows excellent flexibility and is compatible with the integrated circuit process. The mechanical property measurement of the SiNM with nanoscale thickness is critical. A suspended SiNM (40 nm thick) for mechanical measurements is fabricated by transferring a chemically etched ultrathin monocrystalline silicon film from silicon on insulator wafer to a substrate with a multi‐hole array. And then, the atomic force probe is utilized to load force on the free‐standing SiNM to obtain a force deflection curve, and then the Young's modulus of such floating SiNM can be directly calculated based on the large deflection plane model. It shows that the Young's modulus of such SiNM is basically consistent with that of the bulk silicon. However, the SiNMs’ floating area significantly affects the results, i.e., the Young's modulus varies with the ratio of the suspended area diameter (i.e., hole diameter) to the film thickness. The Young's modulus is independent of hole diameter when the ratio is greater than 425. According to this relationship, the variation of Young's modulus can be predicted for arbitrary thick SiNMs and any transferable nanofilms.

An Improved Correlation for the Estimation of the Yield Strength from Small Punch Testing

This study aims at improving the empirical correlation for estimating the yield strength from small punch tests. The currently used procedure in the European standard EN 10371 to determine the elastic–plastic transition force—based on bi-linear fitting—involves a dependency not only on the onset of plastic flow but also on the work hardening of the material. Consequently, the yield strength correlation factor is not universal but depends on the material properties and on the geometry of the small punch set-up, leading to a significant uncertainty in the yield strength estimation. In this study, an alternative definition of the elastic–plastic transition force is proposed, which depends significantly less on the work hardening of the material and on the small punch geometry. The approach is based on extensive elastic–plastic finite element simulations with generic material properties, including a systematic variation of the yield strength, ultimate tensile strength, and uniform elongation. The new definition of the transition force is based on the deviation of the force-deflection curve from the analytical elastic slope derived by Reissner’s plate theory. A significant reduction of the uncertainty of the yield strength estimation is demonstrated.

Investigation on regression model for the force of small punch test using machine learning

The analytical solution for the force-deflection curve of the small punch test (SPT) is still a challenge. Machine learning is employed in the present study to establish a model for estimating SPT forces by using the strength of a material. The yield strength and ultimate tensile strength of materials and corresponding SPT force-deflection curves generated by finite element simulations are the training and testing data for machine learning. Pearson correlation analysis was performed first to measure the statistical association between the SPT force at a given deflection and the strength of materials. It was shown that a binary linear regression model was capable of correlating SPT forces to the yield strength and ultimate tensile strength of a material. The model parameters were determined after training, and then this model was tested by testing data. The accuracy of the regression model was verified by hypothetical materials, X70 steel and Incoloy 800H alloy. This study gives a new insight into the relationship between force responses of SPT and material properties, and can promote the development of novel approaches for determining material tensile properties using SPT.

Experimental evaluation of fracture properties of aluminum alloy 1050-H14 by small punch test

Although ductile fracture properties of aluminum alloy have been examined by several research works, the effect of strain rate in small punch test is still unclear. An investigation on rate sensitivity of fracture mechanical characteristics of aluminum alloy in small punch test is necessary. In the present study, an experimental investigation of small punch test is performed at different deformation rate in quasi-static test for aluminum alloy 1050-H14. The strain-rate sensitivity of fracture properties are discussed based on the force-deflection curve as well as observation of fracture surface of deformed specimen after testing. The obtained results show that the material possesses a positive rate-sensitivity in the investigated range of displacement rate from 0.48 to 1.26 mm/min. The necking appears in a small region due to inhomogeneous deformation in the direction of cross-section at lower deformation rate. In the case of higher rate of deformation, more uniform deformation in the direction of cross-section and the local ductile fracture with more dimples can be observed.

Research on Mechanical Properties of Winding Axial Bending Under Unbalance of Transformer Pad

To improve the study on the influence of transformer windings and pad support on transformer short-circuit resistance, the calculation method of wire bending elastic modulus is analyzed, and the sample test is carried out: The influences of the unbalance of the two ends of the wire between the number of wires wound and the span of adjacent pads on the force-deflection curve, the bending force at the selected deflection, and the elastic modulus of bending were analyzed. The results showed that: Increasing the number of wires and decreasing the height difference of adjacent pads can improve the bending force and bending elastic modulus of wires, the axial stability, and short-circuit resistance of transformer windings. When the height of the adjacent pad is not balanced, the axial force can increase the compression degree between the pad and the wire, and reduce the span of the wire. Under the action of force, the wire yields twice, which further reduces the bending force and elastic modulus of the wire. This research can provide test data support for improving the installation of transformer winding pads and theoretical evaluation of short-circuit tolerance.

Utilizing End-of-Life Tyre Crumb Rubber in Cement Formulation by Substituting Sand with Different Volume Proportions

Abstract The number of end-of-life tyres recycled into crumb rubber varies widely across different countries and regions, depending on factors such as local regulations, infrastructure, and demand for the product. According to the International Rubber Study Group (IRSG), the global production of crumb rubber from end-of-life tires was estimated to be around 12.7 million metric tons. This study is devoted to the development of cement composites where the sand was partially and fully replaced with a specially prepared fine fraction of crumb rubber. Partial replacement of sand with crumb rubber changes the workability of the concrete. The lighter concrete composite may also have improved acoustic and thermal insulation properties. Complete substitution of sand with crumb rubber leads to a lighter concrete composite, featuring reduced densities and enhanced ductility. In these experiments, prisms of dimensions 40×40×160 mm were produced, with various mixes where we changed the amount of replaced sand with crumb rubber and water-cement ratios. These samples were tested for strength in flexure and compression, simultaneously producing force-deflection curves indicating that the rubber granules prevent brittle failure. By full sand replacement, a lightweight cementitious composite was obtained, with the potential for use as acoustic absorption materials and shock energy absorbing layers, but careful consideration of the specific application and mix design is necessary to ensure optimal performance and sustainability. Replacing sand entirely resulted in a lightweight cementitious composite, with densities of 2222 kg/m3 for 10 % replacement and 1525 kg/m3 for 100 % replacement by volume. This material holds promise for applications in acoustic absorption and shock energy absorption. However, achieving optimal performance and sustainability requires thoughtful consideration of the specific application and mix design.

Performance of a shock isolator inspired by skeletal muscles

Nonlinear vibration isolators with low dynamic stiffness have advantages compared to linear isolators, but they also have limitations in terms of the maximum allowable displacement around a chosen equilibrium position. To overcome this issue, a novel nonlinear isolator is proposed that outperforms the classical quasi-zero stiffness nonlinear isolator when large inputs are applied. In this paper, the response of the isolator when subject to shock excitation is investigated. The isolator suspension is designed to exhibit a quasi-static force-deflection curve with sigmoidal shape, which has been observed in many studies reporting the characteristics of skeletal muscles. The shape of the force-deflection curve is such that the suspension system can store greater elastic potential energy. Simulations show that the proposed four-spring system outperforms the classical nonlinear three-spring configuration, in terms of maximum displacement of a suspended mass, when the shock amplitude is relatively large. This is achieved by exploiting the softening effect for large deformations.

Experimental-numerical-virtual (ENV) modelling technique for composite structure against low velocity impacts

In this paper, an experimental–numerical-virtual (ENV) modelling technique for the FRP composite laminate structures subjected to low-velocity impact loading is presented. The developed system is based on experimental observation, finite element numerical modelling and a damage-visible predictive algorithm relying on the machine learning technique. Both experimental and numerical results are used as training sources for the ENV framework to calibrate then make new predictions. The random damage mechanism is achieved by implementing non-deterministic failure criteria into the FRP composite structure. And the freshly developed clustering based extended support vector regression (C-XSVR) method is adopted to recognize the inherent relations between the variational systematic parameters and the structural progressive damage behaviors by analyzing the modes of induced fiber/matrix damage, energy absorption, and force deflection curves. Stimulating by the continuously changing inputs in real-life environment, different stages of impact process can be predicted by the ENV framework against future forecasted information in a computationally efficient manner. To illustrate the capability and efficiency of the proposed technique, two practical impact applications are fully investigated with both experimental tests and numerical simulations. Predicted impact damage patterns under variational working conditions are then provided and validated against different data sources.

Shear behavior of full-scale prestressed concrete double tee beams with steel-wire meshes

Prestressed concrete double tee (PCDT) members have been widely used in parking buildings with large spans and heavy loads. To investigate the shear behavior of PCDT members, four full-scale PCDT members with steel-wire meshes were tested under monotonic loading in this paper. The two beam-end zones of each specimen were loaded to failure. The parameters studied in-depth were the ratio of the shear span to the effective depth λ and the area of prestressing steel strands. The failure modes, the strain of concrete and steel bars, shear force-deflection curves, cracking load, and shear strength were discussed in detail. The test results show that the variation of the ratio of the shear span to the effective depth λ and the area of prestressing steel strands have a significant effect on the inclined crack distribution of the PCDT members. The deformation capacity of PCDT members increases with an increase in the ratio of shear span to effective depth λ and the area of prestressing steel strands. The shear strength decreases with an increase in the ratio of shear span to effective depth λ and increases with an increase in the area of prestressing steel strands. PCDT members have good crack closure performance and deformation recovery ability after removing the load. Furthermore, an analytical model was proposed to predict the shear strength of PCDT members, which considers the effect of the ratio of shear span to effective depth λ, steel-wire meshes, prestressing steel strands, and the flanges of beams. For an analytical model, the key parameters of the shear-compression zone were established based on the cross-section strain analysis and Rankine's failure criterion. The calculation results show that the proposed model can accurately predict the shear strength of PCDT members. The average predicted-to-test shear strength ratio and the integral absolute error are 0.989 and 0.071, respectively.

Performance of a vibration isolator with sigmoidal force-deflection curve

This paper presents a theoretical insight on the performance of a vibration isolator consisting of a combination of linear mechanical springs arranged to achieve a specific form of geometric nonlinearity. In particular, positive and negative stiffness nonlinearities are combined to achieve a sigmoidal shape of the force-deflection curve, which is proven to be beneficial for vibration isolation purposes when the amplitude of vibration is relatively large. Such behaviour is fundamentally different from that of the classical quasi-zero-stiffness isolator, which presents a low dynamic stiffness at the equilibrium configuration and is thus effective for relatively low amplitude of vibration. The analytical findings are validated by numerical simulations, providing useful guidelines for the design of such isolators.

Finite Element Analysis Methodology for Additive Manufactured Tooling Components

Fused deposition modeling (FDM) for additive manufacturing is constantly growing as an innovative process across the industry in areas of prototyping, tooling, and production parts across most manufacturing industry verticals such as Aerospace, Automotive, Agricultural, Healthcare, etc. One such application that is widely used is for tooling on the shop floor e.g. for pick-off tools, assembly fixtures etc. For tooling applications printing the solid fill component with +45/- 45 raster is common practice. There is a requirement for finite element analysis to validate the strength of 3D printed components for some specific applications in tooling, but due to the anisotropic behavior of 3D printed parts and the unavailability of all mechanical properties FE analysis of 3D printed parts is sometimes challenging. Advance approaches like multiscale modeling approach requires specialized & costly analytical tools. So, to understand the behavior of additively manufactured parts the team has conducted a few tests and compared the results. In this work, solid-filled dog-bone tensile test and three-point bending test specimens were printed with +45/-45 raster orientation and tested in the lab. Tensile test specimens were built with flat, on-edge, and up-right orientations and tested to determine the directional properties of young’s modulus. Using mechanical properties from the tension test 3 points bending test is simulated in FE software- ANSYS. The FE modeling was done in two ways, in first model orthotropic properties were assigned to the specimen, and for second model isotropic properties were assigned. For isotropic modeling least value of young’s modulus is used. Simulation results of three-point bending test shows that in the linear region of force-deflection curve, deformation values from FE model with both orthotropic and isotropic modeling are in good agreement with the experimental results. Also, the difference in stress results between isotropic and orthotropic FE model is almost negligible. To support this observation, study is performed for various conditions. The specimens were printed with ABS material on Ultimaker® and ASA material on Stratasys® Fortus 360mc™ machine with T12, T16 and T20 nozzle settings. Study shows, for tooling applications if the 3D printed solid-filled components are designed with a certain factor of safety then validating its strength with isotropic material properties will give acceptable results. The advantage of this approach is getting the isotropic mechanical properties is easy and modeling with FE modeling will be simple.

Comparing the Energy-Stretch Properties of Two Compression Bandage Systems in a Laboratory-Based Test under Controlled Conditions.

ABSTRACTOBJECTIVETo compare the characteristics of two commercially available compression systems, a dual-compression bandage system (DCS) and a traditional two-layer bandage (TLB), using a laboratory bench test.METHODSThe compression systems were evaluated in a computer-controlled tensile test to generate force-deflection curves for each sample. The compressive work and the theoretical pressure applied to the limb by the respective compression bandages were calculated at the maximum stretch and a stretch instructed by the manufacturers. The manufacturer of the DCS provides reference points on how much the bandage should be stretched to provide the desired pressure, and the TLB stretch was calculated from the product’s datasheet.RESULTSThe combined results of layers 1 and 2 for the DCS showed greater load and work than the TLB at both the maximum and recommended stretch. The recommended stretch for DCS and TLB was less than 50% of the deflection up to the breaking point.CONCLUSIONSThe high work provided by the two layers of the DCS suggests a wider range of performance than the TLB when applied to the lower limb, especially after the limb volume is initially reduced by compression. Moreover, using the tensile test and the guide of the reference points on layers 1 and 2 from DCS, the calculated pressure achieved the expected values stated by the manufacturer. Human studies should be conducted to determine whether the reference points provided by DCS are beneficial for obtaining repeatable values.

Estimation of UTS from small punch test using an improved method

Small punch test is a promising method for evaluating the tensile and fracture properties from small volumes of material especially for assessing material degradation of structural components in service. In this paper, the existing methods to determine ultimate tensile strength (UTS) from small punch test are revisited and an improved method is proposed and validated through finite element analysis and experiments. In the new method, the force corresponding to the inflection point in the slope of force-deflection curve in the membrane stretching regime is identified for UTS correlation. The onset of plastic instability during small punch deformation is associated with this inflection point. The UTS correlation determined from the slope based method exhibited stronger linearity with lower relative error compared to the existing methods for a wide range of material strength and ductility.