Strength Estimation Method Research Articles

Small punch evaluation of mechanical properties for 310S stainless steel considering pre-strain effect

Strain strengthening technology is widely used in practical engineering to increase the allowable stress of materials in pressure vessel manufacturing. Small punch analysis was performed using less material in this study to analyse the influence of pre-strain on the mechanical properties of 310S stainless steel. The results indicated that the material yield strength and ultimate tensile strength increased with pre-strain deformation. Similarly, the small punch characteristic parameters increased owing to the influence of the pre-strain, proving that the small punch test could estimate the evolution of mechanical properties along with pre-strain deformation. Small punch characteristic parameters at different deformation stages were analysed. In addition to the maximum load, small punch parameters at the inflection point were used in the ultimate tensile strength estimation. The small punch deformation features and stress distribution were discussed based on numerical simulations. Finally, an ultimate tensile strength estimation method based on membrane stretching model was proposed. Additionally, the strain hardening parameters considering the effect of pre-strain deformation were discussed.

Predicting concrete strength early age using a combination of machine learning and electromechanical impedance with nano-enhanced sensors

To ensure the structural integrity of concrete and prevent unanticipated fracturing, real-time monitoring of early-age concrete's strength development is essential, mainly through advanced techniques such as nano-enhanced sensors. The piezoelectric-based electro-mechanical impedance (EMI) method with nano-enhanced sensors is emerging as a practical solution for such monitoring requirements. This study presents a strength estimation method based on Non-Destructive Testing (NDT) Techniques and Long Short-Term Memory (LSTM) and artificial neural networks (ANNs) as hybrid (NDT-LSTMs-ANN), including several types of concrete strength-related agents. Input data includes water-to-cement rate, temperature, curing time, and maturity based on interior temperature, allowing experimentally monitoring the development of concrete strength from the early steps of hydration and casting to the last stages of hardening 28 days after the casting. The study investigated the impact of various factors on concrete strength development, utilizing a cutting-edge approach that combines traditional models with nano-enhanced piezoelectric sensors and NDT—LSTMs-ANN enhanced with nanotechnology. The results demonstrate that the hybrid provides highly accurate concrete strength estimation for construction safety and efficiency. Adopting the piezoelectric-based EMI technique with these advanced sensors offers a viable and effective monitoring solution, presenting a significant leap forward for the construction industry's structural health monitoring practices.

Geotechnical properties of natural sand-mixed granulated blast furnace slag applied to the sand compaction pile method

Granulated blast furnace slag (GBFS) has more advantageous properties over natural sand, such as lightweight, higher shear strength, and higher permeability. Therefore, it is regarded as a potentially promising substitute for natural sand in the ground improvement using the sand compaction pile (SCP) method. Due to the relatively rapid solidification, however, which is induced by the latent hydraulic property of GBFS, the permeability of the installed GBFS compaction pile (GBFSCP) decreases quickly, and such an application becomes difficult for the case of SCP with low sand replacement area ratio (LSRAR). So, to decelerate the permeability reduction of GBFSCP, different GBFSs, and natural sands were collected in Japan and Vietnam, and the specimens were prepared by changing the mixing ratio of sand to GBFS from 20% to 80%. Then, firstly, fundamental geotechnical properties of sand-mixed GBFS without hydration were observed. Secondly, the specimens of sand-GBFS mixture were cured in seawater at the temperature of 80°C for 3 days to 380 days. The unconfined compressive strength, permeability, and hydration reaction rate of the hydrated sand-mixed GBFS specimen were measured.
 In conclusion, the geotechnical properties of the unhydrated sand-mixed GBFS become more advantageous than those of natural sand. In addition, by mixing with natural sand, the hydration reaction rate and the solidification of GBFS are controlled. This means that it is possible to keep the compressive strength and the permeability at the predetermined conditions and, in turn, to satisfy requirements for the SCP method with LSRAR. In addition, a simple estimation method of the unconfined compressive strength was proposed for the hydrated sand-mixed GBFS specimen.

녹 면적율과 부식피트 형상비를 이용한 도장강재의 인장강도 추정법

녹 면적율과 부식피트 형상비를 이용한 도장강재의 인장강도 추정법

Fractographic strength estimations of 1- and 2-step, ion-exchanged glass plates fractured in bending

Fractography is routinely applied to estimate the fracture strength of annealed brittle materials, however, it is rarely used in chemically strengthened (CS) glasses displaying significant residual stress. This work expands and improves upon a recently proposed fractographic strength estimation method applicable to CS glass plates with deep, 1-step residual stress profiles and no stress relaxation. In particular, the current work considers both CS soda-lime silicate glass with significant stress relaxation and 2-step, ion-exchanged lithium aluminosilicate glass plates. The proposed methodology and its limitations are discussed in light of extensive testing and analysis carried out on numerous CS glass plates. The accuracy of the proposed correlation between non-dimensional strength and mirror radius was validated on both 1-step and 2-step ion-exchanged glass plates with a relatively small case depth and relatively large, induced surface damage.

Strength estimation method for arbitrary age of cement-treated soil based on high-temperature curing history

Strength estimation method for arbitrary age of cement-treated soil based on high-temperature curing history

A new method for estimation of undrained shear strength of cohesive soil for design use from CPTU

電気式コーン貫入試験（CPTU）結果のみからなる，新たな粘性土の設計用非排水せん断強さ（本論文ではsu(mob)と称す）の評価手法を提案する。この手法は，CPTU から得られるコーン貫入時の過剰間隙水圧から粘性土の正規圧密状態における強度増加率を推定し，得られた値と実効コーン貫入抵抗の一次的関係から算定されるコーン係数を介して su(mob)を評価するものであり，国内外 25 地域 31 地点で得られたデータに基づいている。本手法で求めた su(mob)は，別途室内試験および原位置試験から求めた su(mob)と比較され，その信頼性と適用性を実証している。提案する手法によれば，人的誤差を伴う，ボーリング～乱れの少ない試料採取～室内せん断試験という過程なしに，当地の粘性土の su(mob)を評価できる。

Estimation of in-situ rock strength from borehole geophysical logs in Australian coal mine sites

This study aims to improve the conventional empirical rock strength estimation method that is widely adopted in the Australian coal mining industry and provide more accurate rock uniaxial compression strength (UCS) predictions based on artificial neural network (ANN) models. 274 laboratory-measured UCS data (sample dimension: 60 mm (diameter) × 150 mm (height)) were collected from two longwall coal mines in Australia, along with the four geophysical logs (sonic, gamma, neutron, and porosity logs) and rock density of the tested core specimens. A two-layer ANN model was developed from these data based on the Levenberg–Marquardt algorithm as a base model. As compared to conventional sonic-UCS fitting equations, the mean percentage error, root mean squared error and maximum absolute error of the proposed ANN model were reduced from 34.27%, 15.23 MPa and 70.66 MPa to 20.67%, 11.02 MPa and 47.66 MPa, respectively. Further investigations were conducted by splitting the dataset based on rock lithology and mine locations, and separate ANN models were developed based on the divided subsets. Both lithology-specific and site-specific models exhibited improved estimation accuracy in comparison to the base model, indicating lithology and local geological conditions could considerably affect the estimation accuracy. Among the three types of models, the lithology-specific models yielded the most accurate predictions over the 274 data (MPE: 17.55%; RMSE: 8.84 MPa), followed by the site-specific models and the base model in descending order. Overall, all three models significantly outperformed the current empirical methods adopted in the studied mine sites. The outcomes of this study could provide more accurate UCS predictions for further geotechnical analysis in underground constructions, such as tunnel stability analysis and estimating in-situ stresses based on borehole breakout.

Cyclic Behavior of Interfaces for Seismically Retrofitted RC Buildings

In seismically retrofitted reinforced concrete (RC) structures, new members are connected to existing members using interfaces with roughened surfaces and post-installed dowel bars. During an earthquake, the interfaces are subjected to cyclic shear and normal stresses. Therefore, the structural design of interfaces is essential. In a previous study, normal and shear loads were applied to interface specimens. Moreover, a shear strength estimation method was proposed; however, the cyclic behavior was not discussed. This paper presents a cyclic model of the roughened surface in retrofitted RC structures. First, an envelope model was constructed using the previous shear strength estimation method and Saenz model, a constitutive law of concrete. Subsequently, the cyclic rules were modeled. Moreover, a previous dowel model was incorporated into the proposed cyclic model to estimate the test results. Finally, the proposed model provided reasonably estimated test results; the average ratio of the test results to the model results was 1.04. In addition, as δ increased, the effect of the dowel bar intensified in terms of shear.

Proposal of a simple estimation method of lower limb muscle strength based on function-specific effective muscle theory.

Proposal of a simple estimation method of lower limb muscle strength based on function-specific effective muscle theory.

Verification of Spalling Tensile Strength of Rocks using 3D GPGPU-accelerated Hybrid FEM/DEM

The spalling test is widely applied for evaluating dynamic tensile strength of rock under high strain-rate condition. The dynamic tensile strength is indirectly measured in the spalling test by theoretically assuming the tensile stress level at the failure position of a cylindrical specimen based on the 1D stress wave propagation theory. However, the theoretical estimation method for dynamic tensile strength have not been fully validated since dynamic tensile strength was determined with insufficient understanding of the fracture process, such as crack propagation and stress distribution in the rock specimen during the spalling test, owing to observational limitations in the experiment. Thus, a proper validation method is required for the proposed method, and numerical simulation can be used to validate the proposed method by reproducing the tensile fracture process of the rock specimen during the spalling test. Thus, the dynamic spalling tensile test for rock specimens was reproduced in this study using the GPGPU-based 3D hybrid FDEM that we recently developed. The dynamic tensile fracturing process was analyzed in the simulation of spalling under various strain-rate conditions. Finally, we discussed the application of various theoretical estimation methods to the 3D spalling test.

Education and Research Related to Welding and Joining Technology: A Study on Strength Estimation Method of Spot Welding by Machine Learning

Education and Research Related to Welding and Joining Technology: A Study on Strength Estimation Method of Spot Welding by Machine Learning

Evaluating the strength of a beam-type electric switch mechanism housing

Aim. Choice of method and its validation for the purpose of confirming the feasibility of safe operation of a switch mechanism housing submitted to rolling stock axle loads of 30 tf. Method. As of today, there are neither regulations regarding the strength parameters of load-carrying elements of electric switch mechanisms, nor verification procedures. Given the above, when evaluating the strength of electric switch mechanism housing, the authors used the method used for the purpose of evaluating the strength of load-carrying elements of locomotives per GOST R 55513-2013. That method has a long history of application as part of calculation and testing of motive power and has shown good results. According to the method, strength is evaluated by comparing the safety factor of fatigue strength n with the allowed value for steel structures [n] = 2.0. Result. The activities resulted in the validation of the proposed method of strength estimation by the criterion of fatigue strength. The value of fatigue endurance of electric switch mechanism housing was estimated based on the results of fatigue benchmark tests of three items. Each was stressed by stepping up the amplitude of the applied force after the base number of cycles had been reached. At the first stage, the loading was equivalent to the operational value. After the base number of functions had been reached for each item, the following step was initiated. The tests continued until cracks have been found. In the process of testing, the amplitude of stress was recorded at each level of loading. For the purpose of identifying the fatigue strength characteristics, the reduced fatigue strength of the switch mechanism housing was calculated under the hypothesis of linear addition of fatigue damage subject to the condition of deterministic loading and subsequent processing of the findings using statistical methods. The value of fatigue limit has been obtained for the housing of a tie-type electric switch mechanism equal to 48.4 MPa. The safety factor of fatigue strength was found to be equal to 2.86, which is above the minimal allowed value. Conclusion. It has been shown that the housing of a tie-type electric switch mechanism has a sufficient strength as regards the operational static and dynamic loads. Its safe operation when exposed to axle loads of 30 tf has also been confirmed.

Residual Strength Estimation Method of Soft Coal Based on Equivalent Residual Strain Ratio

In underground mining engineering, the residual strength of surrounding rock has an important influence on the secondary stress distribution caused by excavation. Generally, the residual strength of coal can be measured by experiments, but for soft coal, due to its large postpeak deformation characteristics and the limitation of strain sensor range, it is difficult to measure residual strength. Therefore, it is of great practical significance to estimate the residual strength of soft coal with incomplete stress-strain curves. In this paper, a method for estimating residual strength of soft coal based on the ratio of equivalent residual strain to peak strain is proposed. Taking advantage of the characteristics that the strain-softening curve of soft coal decreases approximately linearly in the initial stage, keeping the drop modulus unchanged, the endpoint of the extension line can be determined based on the ratio of equivalent residual strain to peak strain, which is estimated residual strength. There are 342 groups of typical complete stress-strain curves analyzed to determine the value range of the ratio of equivalent residual strain to peak strain. It is concluded that for briquette composed of soft coal, the ratio of equivalent residual strain to peak strain is between 1 and 3.35 when the confining pressure is 0-6 MPa, and the maximum probability interval of the ratio value under different confining pressures is further calculated. When the confining pressure is higher than 6 MPa, the briquette composed of soft coal tends to ideal plastic state after peak. The feasibility of the residual strength estimation method is verified by comparing the numerical simulation results of triaxial compression of coal pillars with the experimental results.

A strength estimation method for aluminum alloy butt welded joints with mismatched mechanical properties

Aluminum alloy thin-walled welded structures have been widely used in automotive lightweight design. However, during the welding process of aluminum alloy sheets, the mismatched welded joints with different microstructure and mechanical properties are formed. The entire mismatched welded joint can be divided into four zones, including welded zone (WZ), hardening heat affected zone (HZ), softening heat affected zone (SZ) and base metal zone (BM). This study aims to analyze the effects of mechanical properties and geometrical characteristics of different welding zones on the load-bearing capacity of aluminum alloy thin-wall welded structures. According to experimental results, the relationship between hardness and ultimate tensile strength was investigated. And then, a tetra-material model of mismatched welded joints was established based on the hardness distribution, and the strength of mismatched welded joints was systematically investigated by numerical simulation. Additionally, the statistical analysis of the relationship between mismatched parameters and the strength of welded joints was conducted through the design of experiments (DOE). The results show that the existence of SZ exerts a crucial role in the loading capacity of the welded joint. The main effects and interactions of geometrical and mechanical properties parameters have a great influence on the load-bearing capacity of welded joints. Moreover, the proposed meta-models could effectively predict the strength of thin-wall welded structures, providing a guideline for evaluating the load-bearing capacity of the complex components with the welded structures.

An improved estimation method of gear fatigue strength based on sample expansion and standard deviation correction

The conventional data processing of gear fatigue staircase test is based on the Dixon-Mood method. Extreme estimates might appear under small-sample condition. To solve the aforementioned limitation, this paper proposes an improved estimated method based on standard deviation correction and sample expansion. Meanwhile, the bending fatigue test is carried out for validation. Results show that the relative error of fatigue strength between the Dixon-Mood method and the proposed method is only 0.51% with 22 samples. As the sample number reduces to 12, the maximum errors of the fatigue strength of the Dixon-Mood method and the proposed method are 12.70% and 5.32%, respectively. To control the maximum error within 10%, the sample number required by the Dixon-Mood method is 14, while the proposed method is 8. The proposed method provides a more effective gear fatigue estimation.

Ring Hoop Tension Test for yield strength estimation: Numerical analysis for a novel correlation method and applicability for mechanical testing of tubes and pipes

The tubes and pipes manufacturing industry characterizes the mechanical properties of their products with a wide selection of standards, but most of them are qualitative testing methodologies. To estimate the mechanical properties from a quantitative point of view there are limited options in standards. In that sense, the standard tensile test is the preferred alternative by the manufacturers, but this option limits the mechanical estimation for the longitudinal direction of the tube–pipe product. Particular efforts have been made to design an alternative mechanical testing procedure to characterize the mechanical properties in the hoop direction of pipes and tubes. The Ring Hoop Tension Test (RHTT) was designed to fill this gap, but it shows limitations related to the required tooling and the influence of the frictional contact between the tooling and the ring specimen. In the nuclear industry, the Small Ring Test (SRT), a miniature test derivated from the RHTT, has been investigated in recent years. In this investigation, a novel RHTT was designed to overcome the limitations of SRT and RHTT, and a new procedure was implemented to estimate the yield strength of tubes and pipes. Numerical FEM simulations were performed to reach an optimum estimation method for the yield strength with the specific geometry of the SRT and a wide selection of pipe geometries with the RHTT. A set of hypothetical materials were designed to perform these analyses, taking into account the influence of Young’s modulus, proportional limit, hardening coefficient (based on the Ramberg–Osgood law), and presence of Lüders bands straining. To verify the results obtained from this numerical FEM analysis, experimental tests (standard tensile tests and RHTTs) and metallographic analysis were performed on aluminum Al 6063 T6 and copper C12200 R360 tubes, showing the capability of this optimized RHTT to estimate the yield strength in the hoop direction for anisotropic tubes and pipes.

A Grip Strength Estimation Method Using a Novel Flexible Sensor under Different Wrist Angles.

It is a considerable challenge to realize the accurate, continuous detection of handgrip strength due to its complexity and uncertainty. To address this issue, a novel grip strength estimation method oriented toward the multi-wrist angle based on the development of a flexible deformation sensor is proposed. The flexible deformation sensor consists of a foaming sponge, a Hall sensor, an LED, and photoresistors (PRs), which can measure the deformation of muscles with grip strength. When the external deformation squeezes the foaming sponge, its density and light intensity change, which is detected by a light-sensitive resistor. The light-sensitive resistor extended to the internal foaming sponge with illuminance complies with the extrusion of muscle deformation to enable relative muscle deformation measurement. Furthermore, to achieve the speed, accuracy, and continuous detection of grip strength with different wrist angles, a new grip strength-arm muscle model is adopted and a one-dimensional convolutional neural network based on the dynamic window is proposed to recognize wrist joints. Finally, all the experimental results demonstrate that our proposed flexible deformation sensor can accurately detect the muscle deformation of the arm, and the designed muscle model and convolutional neural network can continuously predict hand grip at different wrist angles in real-time.

Research on Estimation Method of Lower Limb Muscle Strength Based on Surface Electromyography

Research on Estimation Method of Lower Limb Muscle Strength Based on Surface Electromyography

Creating and Formulating Master Diagrams for Fatigue Strength Estimation of Machine Parts and Structural Elements

In the present study, a practical methodology for creating and formulating a master diagram which is utilized for fatigue strength estimation of machine parts and structural elements is discussed. The consideration proceeds based on the correlation parameter between fatigue strength of smooth and notched specimens “Equivalent cyclic stress ratio REQ” that is followed by “Size-dependent magnification factor FSkM1”. The master diagrams originally represent the axial load fatigue strength diagrams of smooth specimens and therefore they are determined as material-specific diagrams without depending on the shape and dimensions of the cross-section. However, they are mainly derived from axial load fatigue strength data of laboratory small notched specimens rather than smooth specimens and the derivation is done by the reverse direction procedure against the method of estimating the fatigue strength of the notched specimen from that of the smooth specimen. From a methodological point of view, it is more effective on the contrary. First, the notch fatigue strength estimation method by previous study is reviewed and then next improvements and new idea for the derivation of master diagrams are proposed. Finally, some examples of master diagrams are shown.