Experimental Mechanics最新文献

Background

Assessing embryo quality is crucial for improving in vitro fertilization (IVF) success rates, yet traditional grading methods rely on subjective evaluations by embryologists, leading to potential bias. Hyperspectral imaging (HSI) offers a non-invasive approach to embryo assessment by capturing detailed spectral information beyond conventional grayscale images.

Objective

This study aims to investigate the effectiveness of HSI in predicting embryo quality and to compare its classification performance with grayscale images, using maternal human chorionic gonadotropin β (β-HCG) levels as labels.

Methods

HSI of embryos obtained from National Taiwan University Hospital were analyzed, with β-HCG levels categorized into three groups. Machine learning models were trained and evaluated using confusion matrices, Cohen’s kappa coefficient, and receiver operating characteristic (ROC) curves to assess classification performance.

Results

The findings indicate that HSI significantly improves classification accuracy compared to grayscale images, particularly in identifying embryos with medium β-HCG concentrations. HSI-based models outperformed random classification, demonstrating enhanced predictive capability in embryo quality assessment.

Conclusions

This study is the first to use β-HCG levels as classification labels, reducing subjective bias in embryo evaluation. The results highlight the potential of HSI as an objective and reliable tool for embryo quality assessment, paving the way for improved decision-making in assisted reproductive technologies.

Background

Many manufacturing processes introduce non-homogeneous distributions of residual stress (RS) in components. Accurate measurement of such stresses requires localized techniques with high spatial resolution, which presents a considerable challenge.

Objectives

This study presents an experimental procedure for mapping non-homogeneous RS using incremental hole drilling (IHD) with small-diameter end mills.

Methods

A multi-magnification stereo digital image correlation (stereo-DIC) system, equipped with parfocal zoom lens optics, is used to capture full-field displacements around drilled holes ranging from 3 mm down to 0.5 mm in diameter. Schajer’s optical formulation—based on displacement fields rather than local strain readings—is applied to quantify RS. The dependence of RS values on end mill diameter is analyzed as a benchmark to assess the reliability of the measurements.

Results

For IHD with small-diameter end mills, fluorescent speckling offers several advantages over conventional black-and-white speckling, including reduced noise, improved stability, and facile detection of the datum plane. Optimal drilling parameters for minimizing deformation are strongly influenced by end mill diameter. The Schajer’s optical formulation leads to high consistency due to its insensitivity to filter size, a common source of uncertainty in DIC-based measurements. Consequently, RS values show weak and unsystematic dependence on end mill diameter, reinforcing the robustness of the approach. Finally, non-homogeneous RS distributions of a dissimilarly welded 304 stainless steel block is mapped.

Conclusion

The proposed experimental method enables a reliable and high-resolution assessment of non-homogeneous RS distributions.

Background

It is of great significance to study the internal and surface crack extension of rock. Currently, there are few studies on quantitative observation of internal deformation of rocks, and there is a lack of correlation analysis between internal and external deformation.

Objective

The objective of this study is to develop a test method capable of testing the internal deformation and stress deflection towards the rock, and to investigate the relationship between the model surface cracking and the internal stress change, the evolution law of the rupture mechanism during the model cracking process, and the influencing effect played by the compressive strength.

Methods

The techniques employed in this study include the embedded strain-cubes technique, digital image correlation system and acoustic emission technique, and rock-like models.

Results

Select the upper end of the prefabricated fissure for analysis, during the yield stage, the maximum local principal strain in the model increases significantly, and the growth is more obvious in the dilatation quadrants, the number of small-scale tensile cracks in the model increases, and the local deformation parameters within the model are strongly correlated with both the overall model strain and the cumulative acoustic emission energy.

Conclusions

As the strength decreases, the model is less prone to local deformation before the yield stage, the model plastic deformation is obvious, the fluctuation of the deflection angle is gradually distributed from the yield stage to the compaction stage, and the rupture mode transitions from being predominantly shear-dominated damage to a mixed tensile-shear failure mechanism.

Background

In optical metrology systems, such as fringe projection profilometry, cameras with lens systems are used to obtain images that allow calculations of three-dimensional shapes of objects with high precision and quality, so it is necessary to minimize all sources of error that may affect measurements.

Objective

We propose an experimental method that enables the portability of chromatic aberration calibration when a lens is interchanged between cameras in optical setups.

Methods

The method consists of compensating for errors through a chromatic aberration calibration process in two different cameras (monochromatic and color cameras) and comparing both calibrations, verifying that they are similar.

Results

The results demonstrate that it is possible to generate a chromatic aberration compensation matrix and apply it to any system that uses the same lens. Comparing the results obtained by the cameras shows that the slope variation of the chromatic aberration phase-difference planes lies between 0.0001 and 0.0003 degrees.

Conclusions

The proposed method ensures that chromatic aberration calibration is not limited to a single camera, but can be applied to any system with the same lens, improving measurement accuracy and enabling portability in optical metrology setups.

Background

The experimental sources, e.g. transducers, cameras, etc. involved in increasingly sophisticated experimental studies usually have dissimilar temporal resolutions. The data fusion process involves a synchronization step, either subsampling to the slowest resolution or supersampling to the fastest resolution. The former leads to data loss, while the latter can introduce significant interpolation errors in the case of transient behavior.

Objective

The goal is to develop a methodology to enhance the robustness of time-sensitive material behavior identification, exploiting the full richness of the experimental dataset.

Method

This paper discusses an identification framework based on a multi-phase interpolation method of the boundary conditions using Multi Degree B-splines and the asynchronous definition of cost functions of established inverse methods, namely Finite Element Model Updating and Integrated Digital Image Correlation. The approach is validated through the identification of viscoelastic constitutive parameters of a polymer 3D-printed specimen on both synthetic and real uniaxial and biaxial experiments.

Results

The proposed methodology enhances signal-to-noise ratios and time-dependent parameter identification quality without unnecessary data inflation.

Background

Compared to gas-driven shock tubes, the explosively driven shock tubes (EDSTs) in straight form are more applicable to simulate explosive shock wave. However, there are still few studies on the propagation characteristics of shock wave and the formation distance of uniformly distributed planar shock wave (referred to as the characteristic distance in this paper) inside the EDSTs.

Objective

The study presents a method for determining the characteristic distance within the EDSTs in straight form and analyzes the differences in characteristic distance, overpressure peak, and impulse of the shock wave under typical cases.

Methods

To ascertain whether the shock wave is planar and uniform at a given distance, a novel method is proposed according to the weighted coefficient of variation (WCV, which is a dimensionless quantity used to characterize the degree of data dispersion) of the peak overpressure and impulse of the shock wave.

Results

The experimental and simulation results show that when shock wave propagates in the tube, the uniform spatial distribution of the impulse and planar spatial form on the wave front are satisfied first. Afterwards, the uniform spatial distribution of the peak overpressure on the wave front is gradually satisfied. Therefore, when the WCV of the peak overpressure tends to be consistently small, it is presumed that the shock wave has reached the characteristic distance.

Conclusions

By using the characteristic distance determination method, it was found out that the characteristic distance is mainly affected by different straight tube models, where the detonation point is located and how the explosive is shaped.

Background

Laboratory earthquakes provide a controlled setting to examine rupture dynamics, such as rupture initiation, termination, speed evolution, and various patterns. However, the fracture energy of ruptures associated with different velocities and interface roughness remains unclear. Existing methods like photo-elasticity, digital image correlation, and strain gauges are crucial for observing stress fields but face challenges in capturing high stress gradients near the rupture tip.

Objective

To overcome the limitations of existing stress field measurement techniques, this study aims to improve the characterization of rupture dynamics and quantify fracture energy with higher accuracy, particularly under varying rupture velocities and interface roughness.

Methods

To achieve this, the digital gradient sensing (DGS) method is refined through integration with real contact area measurements to accurately characterize the rupture velocity and stress field near the rupture tip. Accuracy is validated through comparison with theoretical solutions and through integrated application with digital image correlation. The fracture energy of sub-Rayleigh and supershear ruptures is studied on interfaces with two different roughness levels.

Results

The improved DGS method captures rupture tip location, velocity, and stress intensity factor with high accuracy. The parameter study shows that large field of view and large subset size are effective for capturing dynamic ruptures. Using the improved method, the fracture energy of supershear ruptures was found to be nearly equivalent to that of sub-Rayleigh ruptures for both rough and smooth faults.

Conclusion

The enhanced approach enables quantitative characterization of the rupture tip, potentially enhancing the accuracy and precision of laboratory earthquake observations. Furthermore, this study acts as a reference for the future integration of various dynamic testing methods, promising to provide multidimensional insights into the complex nature of dynamic ruptures.

Background

Localised Spectrum Analysis is a full-field measurement method which enables processing optimal patterns (i.e. checkerboard patterns) and obtaining high metrological performance. However, LSA was still limited to 2D cases.

Objective

This paper presents stereo-LSA, an extension of the method for stereo image pairs, enabling the measurement of the 3D displacement field on sample surfaces engraved with optimal checkerboard patterns.

Methods

A standard stereo procedure is followed. The LSA formulation is updated to take into account global rotations induced by the stereo angle.

Results

The technique is applied to three different cases. A synthetic case is used to validate the stereo implementation, and a comparison is proposed with stereo digital image correlation, routinely used in the community.

Conclusions

Stereo-LSA enables measuring 3D-displacement field on a sample surface prepared with checkerboard patterns, leading to high metrological performance.

Background

Toughness is essential for analyzing the damage and fracture behavior of metals and can be effectively characterized using the Charpy impact test.

Objective

The Charpy V-notch test, based on the German standards DIN EN ISO 148-1 (Metallische Werkstoffe - Kerbschlagbiegeversuch nach Charpy, 2010) and DIN EN ISO 14556 (Metallische Werkstoffe - Kerbschlagbiegeversuch nach Charpy (V-Kerb), 2017), requires test specimens to have a minimum thickness of 10 mm. Therefore, it is unsuitable for thin metal sheets with a thickness of only 2 mm. To address this limitation, a new pendulum test setup and impact tensile specimens using thin metal sheets are designed to evaluate the energy absorption of the investigated high-strength steels S1100A and S1100B.

Methods

The newly designed impact tensile specimens are subjected to various temperatures, ranging from room temperature to -196 (^circ )C, in intervals of 25 (^circ )C. In addition, sub-size Charpy tests are performed to compare with the newly designed impact tensile tests. Scanning electron microscopy is used to examine the fracture surfaces after the experiments, distinguishing between ductile and cleavage fracture behavior.

Results

Different absorbed impact energy–temperature transition curves are obtained for the sub-size Charpy V-notch and impact tensile experiments for the high-strength steels S1100A and S1100B. Additionally, the results reveal that stress states significantly influence the ductile-to-brittle transition curves, as well as different damage and fracture behavior.

Conclusions

The new experimental approach provides an effective method to capture the toughness of thin metal sheets under different stress states. It facilitates understanding damage and fracture behavior under impact loading conditions while accounting for temperature effects.