Traditional Mechanical Testing Research Articles

A Perspective on Democratizing Mechanical Testing: Harnessing Artificial Intelligence to Advance Sustainable Material Adoption and Decentralized Manufacturing

Abstract Democratized mechanical testing offers a promising solution for enabling the widespread adoption of recycled and renewably sourced feedstocks. Locally sourced, sustainable materials often exhibit variable mechanical properties, which limit their large-scale use due to tight manufacturing specifications. Wider access to mechanical testing at the local level can address this challenge by collecting data on the variable properties of sustainable feedstocks, allowing for the development of appropriate, uncertainty-aware mechanics frameworks. These frameworks are essential for designing custom manufacturing approaches that accommodate variable local feedstocks, while ensuring product quality and reliability through post-manufacturing testing. However, traditional mechanical testing apparatuses are too costly and complex for widespread local use by individuals or small, community-based facilities. Despite promising efforts over the past decade to develop more affordable and versatile testing hardware, significant limitations remain in their reliability, adaptability, and ease–of-use. Recent advances in artificial intelligence (AI) present an opportunity to overcome these limitations by reducing human intervention, enhancing instrument reliability, and facilitating data interpretation. AI can thus enable the creation of low-cost, user-friendly mechanical testing infrastructure. Future efforts to democratize mechanical testing are expected to be closely linked with advancements in manufacturing and materials mechanics. This perspective paper highlights the need to embrace AI advancements to facilitate local production from sustainable feedstocks and enhance the development of decentralized, low-/zero-waste supply chains.

Application of image processing technology based on field programmable gate array in mechanical part inspection

Introduction: In the field of industrial manufacturing, accurate inspection of mechanical components such as gears and bearings is of Paramount importance. However, the traditional mechanical testing methods are often disturbed by human factors, which not only affects the stability of the test results, but also leads to low efficiency and large error. In order to solve these problems, this research focuses on developing a new edge detection model.Methods: A novel edge detection model based on field-programmable gate array image processing technology was used in this study. The model uses adaptive threshold multi-directional edge detection technology to identify the edge features of mechanical gears and bearings, aiming at improving the precision of detection.Results and Discussion: After performance verification, the running time of the model was controlled within 11 s, and the detection error was limited to less than 9%. Compared with the control group and the experimental group, their performance was superior. Further analysis data show that the detection accuracy of this model is as high as 0.9004, its internal resource utilization rate is 88%, and the detection rate is as high as 91%, which are better than the comparison model.Conclusion: The proposed test model not only significantly improves the efficiency and accuracy of the test, but also fully meets the requirements of the test. This new edge detection model has potential application value in industrial manufacturing field, and provides a new solution for industrial manufacturing quality inspection.

Numerical simulation of concrete strength based on microstructure and mineral composition analysis using micro-CT and XRD technology

The investigation of mechanical properties in porous materials, such as concrete, has been a significant area of interest in the fields of civil engineering and architecture. Traditional macroscopic mechanical testing methods are limited due to destructive experimental conditions, time-consuming procedures, and the inability to characterize internal structures. To overcome these limitations, researchers have utilized microscopic factors with micro-CT and simulation models. Different simulation methods demand mechanical parameters to effectively model the constituent materials; however, there exists variability in the amount and standard values of these input parameters, which leads to a decrease in the reliability of the obtained results. In order to tackle this issue, a novel approach is proposed, which integrates mineral component analysis using X-ray diffraction (XRD) and establishes coefficients to minimize the number of necessary input parameters. Simulation results demonstrate excellent agreement with experimental measurements, accurately reproducing the stages of elastic deformation, failure, and fracture in the stress-strain curve of concrete. Our findings reveal that changes in the concrete skeletal structure, microstructure, and mineral composition significantly influence compressive strength. Coarse aggregates and high-mechanical-performance minerals, in particular, have a substantial impact. Additionally, the mechanical properties show a significant linear relationship with the strength reduction coefficient of aggregates and concrete cores. In conclusion, the proposed method, combining CT scanning and XRD with FDEM, proves to be a reliable and practical approach for accurately assessing the mechanical properties of concrete. This methodology simplifies the intricate processes associated with the time-intensive parameter calibration, leading to a more efficient parameter allocation procedure. As a result, this method enhances concrete design, promotes a better understanding of parameter impacts, and enables accurate prediction of concrete behavior across diverse scenarios.

Resonant ultrasound spectroscopy experimental design and optimization

Resonant Ultrasound Spectroscopy (RUS) is a nondestructive material characterization technique that utilizes solid body resonances to estimate elastic moduli. This method is advantageous over traditional mechanical testing due to the significantly lower number of required samples to estimate the same number of moduli. The goal of this project is to develop a high-throughput RUS system capable of measuring experimental resonances and mode shapes in a fraction of the time of traditional RUS measurements. A new system was designed which leverages data/image analysis algorithms to aid in sample alignment and data collection. A standardized sample geometry was also analyzed by performing a geometric sensitivity study and optimizing the aspect ratio of lengths of a parallelepiped. The results show that the optimized sample geometry is consistent between materials with varying elastic properties. In order to validate the design of the new RUS system a comparative study to an existing system was conducted. The results show that the newly designed system produces comparable resonant frequency and mode shape measurements.

Hyperelastic constitutive model parameters identification using optical-based techniques and hybrid optimisation

AbstractIn this paper we propose a new optical-based technique to identify the constitutive relation coefficients of the hyperelastic material using a hybrid optimisation approach. This technique can be used in place of traditional mechanical testing of elastomers for applications that involve inhomogeneous deformation. The purpose of the proposed method is to identify the incompressible hyperelastic material constitutive relation coefficients using a single experiment under different loading cases. The method comprises sample surface 3D reconstruction and uses finite element simulations to replicate the experiments, and uses a hybrid optimisation technique to minimise the error between actual 3D deformations and FE simulation results. The proposed hybrid technique predicts the hyperelastic constitutive relation coefficients more accurately than other optimisation methods. This study introduces a novel approach by employing a subpixel image registration algorithm for 3D reconstruction. The method requires a single experiment with diverse loading cases to accurately determine the coefficients of hyperelastic constitutive relations. The setup is portable and can be accommodated in a small suitcase. For this purpose, an apparatus was constructed comprising a stereoscopic system with eight cameras and a six-degree-of-freedom force-torque sensor to measure the induced forces and torques during the experiments. We identified the constitutive relation coefficients of Ogden N1, Ogden N3, Yeoh, and Arruda-Boyce relations which are commonly used models for silicone materials, using a traditional uniaxial test, optical uniaxial test (experiments performed using a constructed optical system), and inhomogeneous deformations tests. The study demonstrated that the coefficients obtained from inhomogeneous deformation tests provided the most accurate FE predictions. It was also shown that hyperelastic constitutive relation coefficients obtained from traditional uniaxial tests are insufficient to describe the material behaviour when the material undergoes inhomogeneous deformations.

Determination of fracture toughness and yield strength of Inconel 718 by milling operation

This paper presents an analytical scheme to determine the fracture toughness and the yield strength of Inconel 718 by the widely used milling operation. It is noted that there exists material fracture at the tool tip and the removed layer of material undergoes plastic deformation along the primary shear plane. The fracture toughness is considered at the tool tip and the yield strength is applied on the primary shear plane. Subsequently, the modified Williams’ model and the modified Williams-minimization model are both proposed on the basis of the geometries and mechanics in the oblique cutting process. The modelling framework indicates that milling can be developed as an alternative method to determine the fracture toughness and the yield strength from the serrated chip thicknesses combined with the corresponding cutting forces. This is because the experimental method by milling is a convenient scheme as it only requires the cutting forces per unit width of cut with respect to a series of uncut chip thicknesses. In addition, the normal shear angle is predicted by applying the principle of energy minimization. Finally, milling experiments are conducted to validate the two proposed methods. Results show that the two analytical methods return similar values of fracture toughness and yield strength, respectively. Besides, it is noted that high values of yield strength are achieved based on Tresca criterion, which would indicate work hardening in the primary shear zone during the serrated chip formation. The proposed methods exhibit advantages of convenience and generality to derive the fracture toughness and the yield strength, since it is still a challenge for the traditional standard mechanical tests for Inconel 718 due to its toughness and ductility.

Compressive Strength Prediction of Cemented Backfill Containing Phosphate Tailings Using Extreme Gradient Boosting Optimized by Whale Optimization Algorithm

Unconfined compressive strength (UCS) is the most significant mechanical index for cemented backfill, and it is mainly determined by traditional mechanical tests. This study optimized the extreme gradient boosting (XGBoost) model by utilizing the whale optimization algorithm (WOA) to construct a hybrid model for the UCS prediction of cemented backfill. The PT proportion, the OPC proportion, the FA proportion, the solid concentration, and the curing age were selected as input variables, and the UCS of the cemented PT backfill was selected as the output variable. The original XGBoost model, the XGBoost model optimized by particle swarm optimization (PSO-XGBoost), and the decision tree (DT) model were also constructed for comparison with the WOA-XGBoost model. The results showed that the values of the root mean square error (RMSE), coefficient of determination (R2), and mean absolute error (MAE) obtained from the WOA-XGBoost model, XGBoost model, PSO-XGBoost model, and DT model were equal to (0.241, 0.967, 0.184), (0.426, 0.917, 0.336), (0.316, 0.943, 0.258), and (0.464, 0.852, 0.357), respectively. The results show that the proposed WOA-XGBoost has better prediction accuracy than the other machine learning models, confirming the ability of the WOA to enhance XGBoost in cemented PT backfill strength prediction. The WOA-XGBoost model could be a fast and accurate method for the UCS prediction of cemented PT backfill.

Evaluation of asphalt mixture micromechanical behavior evolution in the failure process based on Discrete Element Method

Asphalt mixture was a granular material, and traditional mechanical testing methods were difficult to reveal the failure mechanism. To evaluate the micromechanical behavior of asphalt mixture in the failure process, the DEM (Discrete Element Method) model of the uniaxial compression test was established. The virtual aggregate particle database with real morphology properties was constructed, and the linear parallel bond model was used to simulate the adhesion of asphalt. In the DEM model of the asphalt mixture failure process, the movement of asphalt mortar and coarse aggregate was evaluated, and the Discrete Fracture Network (DFN) was proposed to represent the microcrack. Finally, the three-dimensional spherical coordinate histogram was used to analyze the evolution of magnitude and direction of the coarse aggregate skeleton contact force. It found that the movement of coarse aggregate was less than that of asphalt mortar in the process of the uniaxial compression test, and the coarse aggregate movement was affected by its particle size and location. The result also found that although the adhesive and cohesion failure could occur at the same time, the adhesive failure was less than cohesion failure in the early stage of the uniaxial compression test, and the aggregate with larger particle size could reduce the generation of adhesive failure. Compared with the magnitude of coarse aggregate skeleton contact force, the change of direction was the main reason for a decrease in stress when the asphalt mixture specimen exceeded the peak strength.

Influencing Parameters for the Failure Mechanism of Carbon-FRCM (Fibre Reinforced Cementitious Matrix Systems)

Nowadays, FRCM (Fibre Reinforced Cementitious Matrix) systems are highly attractive for the building materials market; thus, their optimization and development cover an essential role. This work points out the chemical and physical parameters influencing the carbon-FRCM mechanical behaviour. Three different FRCMs composed of commercially available carbon fabric and different inorganic matrices are involved. Matrices are specifically developed to enhance the adhesion with the fabric and differ in organic additive used. Moreover, different fabric geometry (twisted and untwisted) and fibre coatings are considered: micro-silica, fine silica aggregate and medium-size silica aggregate. A new shear test setup is designed to obtain an inexpensive characterization method and employs traditional mechanical tests. Morphological and compositional analyses were performed on the surface fractures. On equal reinforcement typology, significant improvements in shear strength are promoted by organic additives and fabric coatings. Also, pull-out test displays that the twisted bundle promoted the fibre-to-matrix adhesion and remarkably modified the sample failure mechanism compared to the untwisted one. Finally, the FRCM mechanical performance is primarily influenced by mechanical adhesion contribution that might be increased by adopting simple geometrical choices or fabric surface treatments.

Quasi-static and intermediate test speed validation of SHPB specimens for the determination of mode I, mode II fracture toughness of structural epoxy adhesives

The study of the behaviour of adhesive joints under impact loadings is a very active field of research, driven by significant industrial interest, such as the automotive industry, in order to improve mechanical behaviour, reduce weight and simplify manufacturing. Furthermore, due to high standards in terms of safety required in the automotive industry, namely the occupant’s safety during collisions, the behaviour of adhesives under impact loads is becoming a prominent object of study. This work proposes a novel and simplified method to experimentally obtain a custom set of TSLs (traction-separation laws) and estimate the fracture energy both for mode I and II that can be tested from quasi-static to impact conditions resorting to a SHPB (Split Hopkinson Pressure Bar) equipment with especially designed specimens. The method is validated by comparing those results to fracture energy values obtained using DCB (Double Cantilever Beam), ENF (End Notch Flexure) and prior validated mixed mode apparatus Finally, the SLJ (Single Lap Joint) behaviour is predicted by resorting to the custom TSLs and comparing model performance to experimental results. With the proposed method the obtained fracture energy was found to be equivalent to that obtained with more traditional fracture mechanical tests used in the field of adhesive bonding. The custom TSLs were able to predict the behaviour of SLJ fairly accurately.

Incorporation of In Situ Synthesized Nano-Copper Modified Phenol-Formaldehyde Resin to Improve the Mechanical Properties of Chinese Fir: A Preliminary Study.

Phenol-formaldehyde (PF) resin, modified using nano-copper with varying contents (0 wt%, 1 wt%, 3 wt%), was manufactured to improve the mechanical properties of Chinese fir. The morphology, chemical, micromechanical and micromechanical properties of the samples were determined by transmission electron microscopy (TEM), atomic force microscopy (AFM), environmental scanning electron microscopy (ESEM), Fourier transform infrared spectroscopy (FTIR), nanoindentation (NI) and traditional mechanical testing. The TEM and AFM results indicated that the in situ synthesized nano-copper particles were well-dispersed, and spherical, with a diameter of about 70 nm in PF resin. From the FTIR chemical changes detected by FTIR inferred that the nano-copper modified PF resin penetrated into the Chinese fir cell walls and interacted with the acetyl groups of hemicellulose by forming a crosslinked structure. Accordingly, the micro-mechanical properties of the Chinese fir cell walls were enhanced after treatment with nano-copper modified PF resin. The filling of the PF-1-Cu resin (1 wt% nano-copper) in the wood resulted in 13.7% and 22.2% increases in the elastic modulus (MOE) and hardness, respectively, of the cell walls. Besides, the impact toughness and compressive strength of the Chinese fir impregnated with PF-1-Cu resin were 21.8% and 8.2% higher than that of the PF-0-Cu resin. Therefore, in situ synthesized nano-copper-modified PF resin is a powerful treatment method for Chinese fir due to improved diffusive properties and reinforcement of the mechanical properties.

Experimental nanomechanics of 2D materials for strain engineering

The past 2 decades have witnessed the explosion of research on two-dimensional (2D) materials, where notable efforts have been made in the synthesis and design of a wide spectrum of applications. To understand their mechanical properties and responses triggered by deformation, the prerequisites for reliable applications under realistic service conditions, novel experimental methods have to be developed due to the limitations of traditional bulk mechanical testing for atomically-thin structures. Besides, the nearly-ideal 2D crystalline structures of many 2D materials endow them the great capability of deformation, showing promising potentials in “strain engineering” and “interface engineering” applications. This review summaries several representative approaches in experimental nanomechanics and corresponding progresses in the characterization of structural and mechanical properties of 2D materials, with the aim to provide insights into the instrumental design for nanomechanical tests. In addition, examples of strain-tuned material behaviors and changes in their performance are also discussed to demonstrate the significance of the nanomechanical approach for functional device design and applications.

Study on the mechanical properties and application prospects of the traditional and modern connection of wood structure

Based on the connection status of traditional wood structure nodes in southeast Guizhou, this paper analyzes the structural performance of traditional and modern connection methods of wood structure buildings, and analyzes the mechanical performance and deformation mechanism of the structure through basic traditional wood structure mechanical tests; Analyze the advantages and disadvantages of different connection methods, summarize the improvement ideas of node connection of residential wood structure buildings; compare traditional and modern wood structure systems, analyze the seismic performance of the structure; provide a reasonable reference for wood structure design. Further realize the industrialization and standardization of regional wood structures.

A poroelastic master curve for time-dependent and multiscale mechanics of hydrogels

Abstract

Initial research of changes in mechanical properties of polymer-graphene composite with use of Digital Image Correlation

The problem of the possibility of using digital image correlation to assess changes in the mechanical properties of a polymer composite with the addition of graphene (1% by weight) in the form of flakes was taken up in the paper. Samples for uniaxial tensile testing were produced by selective laser sintering from polyamide powder particles and multi-flake graphene. In the tests carried out using the three-camera system, a variable strain distribution was recorded in the heterogenic PA-G composite material. Maps developed in the evaluation process – in particular, tangential deformations – allowed to conclude the impact of axial load on PA-G behaviour in time in the area of the polymer matrix, graphene agglomerates, and their interfaces. The research showed that the digital image correlation technique is a perfect complement to traditional mechanical tests when determining the properties of new heterogeneous composites, in particular, polyamide-graphene composite. Real-time observation of changes in the material map allows for a detailed analyzes of complex micromechanical aspects.

Measurement of creep deformation of ex-service 12% Cr steel using digital image correlation

The effective operation of ageing coal-fired power plants requires routine damage assessment of critical component materials throughout their service history. Traditional post-exposure mechanical testing typically requires large amounts of material for each testing condition. This study introduces an accelerated (high stress and temperature) creep testing technique that employs digital image correlation for strain measurement over a non-uniform temperature field generated by a thermomechanical tester. When applied to different ex-service (exposed to service conditions within a power plant) 12% Cr piping steels, multiple accelerated creep curves at temperatures ranging from 550°C to 600°C are measured from a single specimen for each material condition. Higher creep damage in the steel due to longer service exposure and higher void densities is revealed by shorter rupture times, faster creep rates and tertiary-dominated creep curves when compared to the lower creep damage state. Microstructural study via quantitative electron microscopy confirms the dislocation creep-driven growth of subgrains in the specimen gauge regions relative to the grips. Larger subgrains and a weakening of precipitate distributions for the high damage material were also noted. Digital image correlation–measured strains are in good agreement with traditional techniques of creep testing with standard extensometry. On a comparative basis, the technique is shown to be a plausible form of damage assessment of 12% Cr piping steels with varying levels of service exposure and serve as a suitable mechanical complement to the traditional void replica methodology.

Mineralogical, microstructural and porosimetry analysis in three different clayey soils

Diffraction, scanning electron microscope and helium porosimetry techniques have been shown to be suitable for obtaining physical and mineralogical properties in soil samples. The X-ray fluorescence spectroscopy allows obtaining the elemental composition of the sample, while the X-ray diffraction technique permits obtaining a qualitative and quantitative composition of the soil minerals. On the other hand, scanning electron microscope shows the microstructure of the soil and the helium porosimetry measures the pore size, volume, distribution, density and other porosity-related characteristics of the material. This document presents the characterisation of three different clayey soils by an experimental plan that included mineralogical, microstructural and porosimetric tests. The soils used were bentonite, kaolin and a natural clay retrieved near to Bogotá city, Colombia. Results obtained from this study allow providing a better understanding of soil behaviour, which traditional mechanical tests do not explain.

Mechanical Properties of Lithium Metal for Next Generation Batteries

Recent technological innovations such as electrified vehicles and personal electronics have enabled by meaningful advances in lithium ion batteries. Due to long term investment in battery materials and manufacturing, this technology has improved at a relatively steady 8% per year (in terms of specific energy, Wh/kg) since introduction in 1991. To increase the rate of electrified vehicle adoption, revolutionary improvements in battery technology are needed beyond what is currently available. Currently, three chemistries comprise the next generation battery direction; solid-state (SS), lithium-sulfur and lithium-air. All of these chemistries would benefit from the use of lithium metal anodes as one of the primary means of improving energy density. A SS separator of comparable dimensions as a conventional polyolefin separator could lead to ~100% improvement in cell energy density by enabling metallic lithium anodes [1]. Despite the considerable interest and dependence on lithium anodes in future generation batteries, its mechanical properties are poorly understood. The successful integration of pure lithium metal anodes will require understanding and predicting its mechanical behavior under static and cycling conditions. Recently our group investigated the elastic, plastic and creep behavior or lithium metal [2]. This presentation will extend the scope from our previous study emphasizing general property characterization to more battery specific mechanical environments, specifically aspect ratio and strain speed. Modern lithium ion battery electrodes having large surface area to volume ratios yielding low aspect ratios which are very different than traditional mechanical testing (i.e. 2 to 4). Additionally there is growing interest in fast charge/discharge, resulting in relatively short periods of mechanical compression, again different from traditional strain speeds (i.e. 1x10-3 sec-1). The impact of aspect ratio and strain rate on lithium’s mechanical properties will be shown. REFERENCES [1] Albertus, P. et al. Nature Energy, 3 (2018) 16-21. [2] Masias, A. et al. J. Mat. Sci., 54(3) (2018), 2585-2600.

Multimodal Label-Free Imaging for Detecting Maturation of Engineered Osteogenic Grafts.

There is a critical need to develop noninvasive, nondestructive methods for assessing the quality of engineered constructs prior to implantation. Currently, the composition and maturity of engineered tissues are assessed using destructive, costly, and time-consuming biochemical and mechanical analyses. The goal of this study was to use noninvasive, multimodal imaging to monitor osteogenic differentiation and matrix deposition by human mesenchymal stem/stromal cells (MSCs) during in vitro culture. MSCs were encapsulated in alginate hydrogels and cultured in osteogenic conditions for 4 weeks. Samples were evaluated using fluorescence lifetime imaging (FLIm) and ultrasound backscatter microscopy (UBM) prior to traditional biochemical and mechanical testing. Using linear regression analysis, we identified strong correlations between imaging parameters (e.g., fluorescence lifetime and acoustic attenuation coefficient) and destructive mechanical and biochemical tests to assess the maturation of osteogenically induced constructs. These data demonstrate the promise of nondestructive label-free imaging techniques to noninvasively ascertain the progression and maturity of tissue engineered bone grafts.

Scattering spot imaging for the determination of optical and dynamical properties of viscoelastic media

The non-contact evaluation of dynamical properties of media presents several medical, biological, and industrial applications. Diverse optical methods, operating at different scales with various targeted applications, are currently being considered as alternatives to traditional mechanical testing devices. However, the accuracy of most optical techniques upon multiple scattering is compromised by the influence of the medium’s optical properties, namely scattering and absorption. Therefore, in order to accurately estimate dynamical properties, that are related to mechanical features, it is of pivotal importance to determine the medium’s optical properties. In this paper, we present a new simple scheme for the assessment of optical as well as dynamical properties of viscoelastic media. We demonstrate, for the first time, the possibility of estimating absorption, scattering, and dynamical properties using scattering spot imaging with a standard CCD camera at multiple exposure times and with a monochromatic continuous wave (CW) illuminance.