Micromechanical Testing Research Articles

Study of microbially-induced carbonate precipitation for improving coarse-grained salty soil

The salinity of soil can result in serious potential environmental hazards such as increased collapsibility and corrosiveness. Microbially induced carbonate precipitation is an upcoming and pollution-free treatment modality that can eliminate environmental and engineering hazards of saline soil . To verify the feasibility of the method of curing saline soils, a series of tests were conducted to investigate the impact of chloride salt on urea hydrolysis, the impact of the method on engineering and mechanical properties of coarse-grained soils containing chloride salt and the deterioration mechanism of curing effect caused by salt. The study demonstrated that, even though the curing effect of the method is excellent, the negative effect of salt cannot be ignored. With increased salt concentration, the hydrolysis rate and calcium carbonate precipitation efficiency sharply decrease at first and tend to be flatter. The unconfined compressive strength and shear strength of the samples can be greatly improved through the application of the method. However, calcium carbonate content reduces with an increase in the salt content, which decreases the strength. Compared to uncured samples, the permeability coefficient of cured samples reduced from 1 to 2 orders of magnitude. On the other hand, as the dominant aperture size increases with a decrease in the calcium carbonate content, the permeability coefficient increases with an increase in the salt content. Furthermore, micro-mechanical tests, such as X-ray diffraction and scanning electron microscope tests, were conducted to analyze the mechanism by which salt degrades the reinforcement. As a guiding agent, while chloride salt can improve the proportion of calcite in calcium carbonate, it decreases the total quantity of calcium carbonate through the limiting urea hydrolysis process . A significant amount of calcium carbonate is deposited on the surface of the particles in each sample, especially the contact surface. In conclusion, even though salt has a certain deterioration effect, microbially-induced carbonate precipitation is still an effective and environment-friendly method to cure saline soil. This study can provide a theoretical basis for using this method to solidify saline soil.

Viscoporoelasticity of coagulation blood clots

A blood clot is an essential biological tissue in physiological hemostasis and pathological thrombus in human bodies. In both physiological and pathological activities, the blood clots are often under external force from the blood flow. Quantifying the mechanical properties of the blood clot is important for the diagnosis and treatment of bleeding disorders and thrombotic diseases. In this work, the blood clot is shown to be viscoporoelastic and its properties are quantitatively characterized through combined rheology and indentation measurements. First, the viscoelasticity of the blood clot is determined by the shear rheology measurement because shear deformation does not induce volume change, and thus does not invoke the poroelastic behavior (i.e., coupled solvent migration and deformation) of the blood clot. Subsequently, an indentation test is carried out. Using a micromechanical testing machine, a spherical bead is pressed onto the blood clot to a certain depth and held for a period, meanwhile, the force is measured as a function of time. The force relaxation is contributed by both viscoelastic and poroelastic effects. Since the viscoelasticity of the blood clots has been fully characterized in shear rheology, the indentation data is used to determine the poroelastic properties of the blood clots. A general viscoporoelastic model is formulated and based on this model the relaxation indentation problem is simulated. By fitting the experimental force relaxation curves with the simulation results, the poroelastic parameters including permeability and drained Poisson’s ratio are obtained. Interestingly, the value of the drained Poisson’s ratio of the blood clot is very close to zero. To verify this behavior, we also carry out unconfined compression measurements to directly observe the volume evolution of the blood clot. The small value of drained Poisson’s ratio is validated by the unconfined compression result. Using the viscoporoelastic parameters determined in this work, we discuss the contribution of solvent migration and viscoelastic effect on the apparent modulus of the blood clot in physiologically relevant conditions. The high poroelasticity indicates the blood clot can withstand high instantaneous loads in the normal direction by resistance to solvent migration. Both poroelastic and viscoelastic processes dissipate energy, and thus could delay the fracture process of the material. This study systematically measures the viscoporoelastic properties of the blood clot and provides an understanding of the contributions of the two mechanisms to the time-dependent responses of coagulation blood clots.

Size-dependent to size-independent transition in creep of single crystalline Cu micropillars

Micromechanical tests are performed to investigate the sample size effects on creep behavior of single crystalline Cu micropillars at room temperature. We report a transition from size-dependent to size-independent creep, where the transition size decreases with increasing holding stress. Furthermore, we find that the stress-related transition from size-dependent to size-independent creep can be explained by the competition between thermally-activated dislocation generation from sources and thermally-activated dislocation motion. Based on this competition mechanism, a quantitative model is established to further formulate the transition, where the model predictions agree well with the experimental results.

Precipitation-based grain boundary design alters Inter- to Trans-granular Fracture in AlCrN Thin Films

Despite their high hardness and indentation modulus, nanostructured crystalline ceramic thin films produced by physical vapour deposition usually lack sufficient fracture strength and toughness. This brittleness is often caused by underdense columnar grain boundaries of low cohesive energy, which serve as preferential paths for crack propagation. In this study, mechanical and structural properties of arc-evaporated Al0.9Cr0.1N thin films were analyzed using micromechanical tests, electron microscopy, atom probe tomography and in situ high-energy high-temperature grazing incidence transmission X-ray diffraction. Vacuum annealing at 1100°C resulted in the formation of regularly-distributed globular cubic Cr(Al)N and elongated cubic CrN precipitates at intracrystalline Cr-enriched sublayers and at columnar grain boundaries with sizes of ∼5 and ∼30 nm, respectively. Consequently, in situ micromechanical testing before and after the heat treatment revealed simultaneous enhancement of Young's modulus, fracture stress and fracture toughness by ∼35, 60 and 10%, respectively. The annealing-induced concomitant improvement of toughness and strength was inferred to precipitations observed within grains as well as at grain boundaries enhancing the cohesive energy of the grain boundaries and thereby altering the crack propagation pathway from inter- to transcrystalline. The here reported experimental data unveil the hitherto untapped potential of precipitation-based grain boundary design for the improvement of mechanical properties of transition metal nitride thin films.

Evolution of the fracture properties of arc evaporated Ti1-xAlxN coatings with increasing Al content

Although the positive effect of an increasing Al content in Ti1-xAlxN hard coatings within the cubic regime is thoroughly investigated, there is a lack of systematic studies on the fracture properties. Thus within the present work, seven Ti1-xAlxN coatings with increasing Al content from x = 0 up to x = 0.78 were deposited by cathodic arc evaporation. Using scanning electron microscopy and X-ray diffraction, a grain refinement with increasing Al content up to x = 0.65 could be observed, while the coating with the highest Al content of x = 0.78 showed again a coarser grain size. The presence of a single phase face-centered cubic (fcc)-structure up to an Al content of x = 0.49 was confirmed by X-ray diffraction. Ti0.44Al0.56N and Ti0.35Al0.65N exhibited a dual phase fcc- and wurtzitic (w)-structure, where for the latter the w-structure is dominating. A single phase w-structure was observed for the Ti0.22Al0.78N coating. Nano-indentation experiments revealed an increasing hardness with increasing Al content up to x = 0.56 and thus, as long as the fcc-phase is dominating, due to decreasing grain size and increasing compressive stress. For the coatings with dominating and pure w-structure a drop in hardness was observed. Similar to the hardness, the micromechanical bending tests also revealed improving fracture properties with increasing Al content up to x = 0.56 and deteriorating fracture properties when the w-structure becomes dominant.

High‐Throughput Micromechanical Testing Enabled by Optimized Direct Laser Writing

Direct laser writing by two‐photon lithography enables the manufacturing of tailored 3D objects, commonly referred to as 3D‐printing, with submicrometer precision. Thereby, new approaches are enabled for miniaturized optical and mechanical devices, where basic material properties act as design guideline and initial input for finite element simulation‐driven device design. These mechanical properties are accessible through micromechanical testing and suitably adapted miniaturized specimens. With direct laser writing, a micromechanical specimen geometry can be readily manufactured without additional postprocessing, enabling the possibility of repetitive sample production and further high‐throughput testing. Widely overhanging features, as in common bending beam or tension specimens, easily cause floating layers as writing artifacts and thereby undefined geometries. Within this work, an approach to overcome this issue is presented. By introducing a slight taper within the geometry at initially printed layers, a reliable sample geometry is achievable without changing the overall mechanical behavior. As showcase geometries, miniaturized notched cantilever and advanced push‐to‐pull devices incorporating a notched tension specimen are detailed. Mechanical testing is conducted in situ and ex situ, and the mechanical influence from introducing a taper to a straight geometry is assessed via a finite element modeling. Thereby, a comprehensive approach for high‐throughput micromechanical testing is established.

Assessing the intimate mechanobiological link between human bone micro-scale trabecular architecture and micro-damages

The dramatic increase in fragility fractures and the related health and economic burden rise the urge of a cutting-edge perspective to anticipate catastrophic fracture propagation in human bones. Recent studies address the issue from a multi-scale perspective, elevating the micro-scale phenomena as the key for detecting early damage occurrence. However, several limitations arise specifically for defining a quantitative framework to assess the contribution of lacunar micro-pores to fracture initiation and propagation. Moreover, the need for high resolution imaging imposes time-demanding post-processing phases. Here, we exploit synchrotron scans in combination with micro-mechanical tests, to offer a fracture mechanics-based approach for quantifying the critical stress intensification in healthy and osteoporotic trabecular human bones. This is paired with a morphological and densitometric framework for capturing lacunar network differences in presence of pathological alterations. To address the current time-consuming and computationally expensive manual/semi-automatic segmenting steps, we implement convolutional neural network to detect the initiation and propagation of micro-scale damages. The results highlight the intimate cross talks between toughening and weakening phenomena at micro-scale as a fundamental aspect for fracture prevention.

Innovative wicking and interfacial evaluation of carbon fiber (CF)/Epoxy composites by CF tow capillary glass tube method (TCGTM) with Tripe-CF fragmentation test

For improvement of mechanical property and manufacturing efficiency of fiber reinforced composites, wettability, which was affected by temperature, viscosity, the pressure of resin injection, fiber volume fraction, fiber array, and so on, was important factor, which had been focused many researchers. Although the wettability during manufacturing processing was usually evaluated by the permeability, it does not contain the surface energies for the fiber and matrix. Using innovative CF tow capillary glass tube method (TCGTM), this study investigated the wetting, wicking and interfacial properties for three type CFs reinforced epoxy composites combined with a triple-fiber fragmentation test. The CFs TCGTM was performed to evaluate wettability and wicking of CF tow with epoxy resin by measuring height of impregnated epoxy front in capillary tube more practically. After curing the specimens, contact angle between CF and epoxy was measured using FE-SEM photos directly. Wetting and wicking were also evaluated by measuring the impregnated length of epoxy droplets on CF tow, and compared with result by CF TCGTM. From all of the relating tests, the 50C type CF exhibited better wetting and wicking than 60E type CF and the desized CF. Interfacial shear strength (IFSS) were evaluated using a triple-fiber fragmentation test for three different type CFs. Better IFSS of the 50C type CF was consistent with wetting and wicking results by CFs TCGTM. A new innovative CF TCGTM can be applicable for conventional CF reinforced epoxy composites more practically by combining with micromechanical test for the IFSS between single CF and epoxy mainly.

Elastic Characterization of Shale at Microscale: A Comparison between Modulus Mapping, PeakForce Quantitative Nanomechanical Mapping, and Contact Resonance Method

Summary Because of the extremely high resolution and little damage to the sample, micromechanical mapping methods have been widely used for elastic characterization of shale at microscale. However, few studies have investigated connections and differences among commonly used micromechanical mapping methods. The influencing factors of micromechanical tests, such as sample preparation, experimental setup, and data processing, have not yet been sufficiently discussed. In the presented paper, three representative micromechanical mapping methods, including modulus mapping (MM), PeakForce quantitative nanomechanical mapping (PFQNM), and contact resonance (CR) method, were systematically compared from theory to application. The fundamental principles of the three methods were introduced, and connections in theoretical background were discussed. A shale sample from the Yanchang Formation in the Ordos Basin was selected for elastic characterization. Mechanical tests were performed on a fixed area on the sample surface by using different methods. The modulus distribution images obtained by the three methods intuitively exhibited microheterogeneity in shale. The influences of scanning frequency, peak force frequency, and force setpoint were analyzed based on the test results. The comparison of the contact area revealed that MM possessed the lowest spatial resolution with the experimental setup, and the CR method was less sensitive to the surface condition than PFQNM. The effectiveness of the data processing method was demonstrated through scale dependency analysis, and the limitations of the test methods were discussed. This work may contribute to improved understanding and selection of micromechanical mapping methods and experimental design of elastic characterization of shale.

Chemo-mechanical effects on the cutting-induced mixed-mode II-III fracture of martensitic stainless steels: An in-situ investigation

Coated carbide-rich martensitic stainless steels are typically used for sharp edges because of their high wear and corrosion resistance. Yet they fail under the combined chemo-mechanical actions of the harsh environment they operate in, and under the mixed mode II-III stress they are subjected to. To investigate this complex failure process, we exposed sharp edges to increasing corrosion severity and carried out in-situ electron microscopy cutting experiments with two micro-mechanical testing setups: a Deben Gatan micro-tensile deformation stage and a Hysitron PI 88 Picoindenter. At low corrosion levels, byproducts formed on the surface are removed during cutting, and cracks propagate at an angle with respect to the sharp edge to form a chip. As corrosion severity increases, a percolated void structure develops in the substrate and cracks propagate perpendicularly to the sharp edge, with portions of the material bending out-of-plane. At high corrosion, a chromium-rich oxide forms in place of the percolated void structure and the material becomes brittle and unable to withstand any applied stress. Although increasing corrosion severity increases the cutting force, our numerical investigation suggests that the formation of the percolated porous structure, which in turn increases substructural heterogeneity in the material, is responsible for the change in crack propagation direction and failure mechanism.

Subchondral bone plate thickness is associated with micromechanical and microstructural changes in the bovine patella osteochondral junction with different levels of cartilage degeneration

The influence of joint degeneration on the biomechanical properties of calcified cartilage and subchondral bone plate at the osteochondral junction is relatively unknown. Common experimental difficulties include accessibility to and visualization of the osteochondral junction, application of mechanical testing at the appropriate length scale, and availability of tissue that provides a consistent range of degenerative changes. This study addresses these challenges.A well-established bovine patella model of early joint degeneration was employed, in which micromechanical testing of fully hydrated osteochondral sections was carried out in conjunction with high-resolution imaging using differential interference contrast (DIC) optical light microscopy. A total of forty-two bovine patellae with different grades of tissue health ranging from healthy to mild, moderate, and severe cartilage degeneration, were selected. From the distal–lateral region of each patella, two adjacent osteochondral sections were obtained for the mechanical testing and the DIC imaging, respectively. Mechanical testing was carried out using a robotic micro-force acquisition system, applying compression tests over an array (area: 200 μm × 1000 μm, step size: 50 μm) across the osteochondral junction to obtain a stiffness map. Morphometric analysis was performed for the DIC images of fully hydrated cryo-sections. The levels of cartilage degeneration, DIC images, and the stiffness maps were used to associate the mechanical properties onto the specific tissue regions of cartilage, calcified cartilage, and subchondral bone plate.The results showed that there were up to 20% and 24% decreases (p < 0.05) in the stiffness of calcified cartilage and subchondral bone plate, respectively, in the severely degenerated group compared to the healthy group. Furthermore, there were increases (p < 0.05) in the number of tidemarks, bone spicules at the cement line, and the mean thickness of the subchondral bone plate with increasing levels of degeneration.The decreasing stiffness in the subchondral bone plate coupled with the presence of bone spicules may be indicative of a subchondral remodeling process involving new bone formation. Moreover, the mean thickness of the subchondral bone plate was found to be the strongest indicator of mechanical and associated structural changes in the osteochondral joint tissues.

Probing the constitutive behavior of microcrystals by analyzing the dynamics of the micromechanical testing system

Probing the constitutive behavior of microcrystals by analyzing the dynamics of the micromechanical testing system

Green Synthesis of Soy Protein Nanocomposites: Effects of Cross-Linking and Clay Nanoparticles on the Mechanical Performance.

A green synthesis scheme was adopted for preparation of soy-protein-based clay nanocomposites, in which soy protein isolates (SPIs) were utilized as the biodegradable resin and clay nanoparticles (CNPs) were used as the nanoreinforcing phase. Cross-linking of the SPIs was realized through an aqueous reaction scheme with oxidized sugars (e.g., glucose and sucrose as the typical constituents of soy flours) as the cross-linkers. Toughening effects of the cross-linkers, process parameters, and CNPs on the mechanical properties (e.g., tensile strength, stiffness, strain at break, and toughness) of the resulting SPI-based clay nanocomposites were examined by micromechanical tensile testing. The cross-linking and toughening mechanisms of the SPI-based nanocomposites were evaluated by Fourier transform infrared spectroscopy, sol–gel and color characterization, scanning differential calorimetry, and transmission electron microscopy. Thermal stability of the cross-linked SPIs was evaluated by thermogravimetric analysis. Experimental results show that cross-linking can noticeably improve both the tensile strength and tensile modulus of the resulting SPI films, and a small quantity of CNPs can obviously alter the mechanical properties of the resulting clay nanocomposite films. The present study indicates that defatted soy flours can be directly utilized for developing low-cost, SPI-based nanocomposites without the need for external plasticizers, and the entire synthesis is completely green without involvement of any petroleum-based organic solvents, polymers, and metallic catalysts. Such biodegradable SPI-based green nanocomposites have the potential to substitute fossil-based plastics and polymer composites for use in various industrial products and house utilities.

Microstructural and micro-mechanical investigation of cathodic arc evaporated ZrN/TiN multilayer coatings with varying bilayer thickness

Modifying the architecture of multilayer hard coatings allows to adjust the mechanical properties of these materials for a given application. Within this work, the effect of the bilayer thickness (Λ) and the individual sublayer thickness ratio on the microstructure and mechanical properties of ZrN/TiN multilayer coatings was investigated. Multilayer coatings with Λ of 570, 320 and 35 nm were deposited by cathodic arc evaporation and compared to TiN and ZrN single-layer coatings. The microstructure was investigated by X-ray diffraction (XRD) and scanning electron microscopy. All coatings exhibit a single phase face-centred cubic structure and a predominant (111) texture. A columnar structure was observed for all coatings and grain growth extending beyond the ZrN/TiN interfaces was evident in all multilayers. For all coatings, compressive residual stresses were determined by XRD using the sin 2 ψ method, where the multilayer sample with the largest Λ exhibited the highest compressive residual stress of −1.7 ± 0.2 GPa. Lower compressive residual stresses could be correlated with decreasing Λ and decreasing ZrN:TiN thickness ratio. Nanoindentation experiments as well as micro-mechanical bending tests were conducted to assess the mechanical properties of the coatings. The ZrN/TiN multilayer sample with Λ of 35 nm showed the highest hardness of 28.0 ± 1.1 GPa. This value is similar to the TiN single-layer and higher compared to the ZrN single-layer, which exhibited a hardness of 27.9 ± 1.4 GPa and 25.8 ± 1.3 GPa, respectively. While the ZrN single-layer showed the highest fracture toughness, the ZrN/TiN multilayer samples were identified as the mechanically stiffest and strongest of the investigated coatings, since they exhibited a higher fracture stress compared to the single-layer coatings. The obtained results allow to optimise the architecture of ZrN/TiN multilayer coatings yielding the desired coating properties for application in the cutting industry. • Arc evaporated ZrN/TiN multilayer coatings with varying bilayer thickness Λ • Smaller Λ leads to grain refinement and more pronounced (111) texture. • Multilayer coating with lowest Λ exhibits the highest hardness. • Highest fracture toughness for ZrN single-layer coating • Improved fracture stress for multilayers compared to single-layers

Additive Manufacturing of Microcantilevers of Varying Stiffnesses for Sensing Applications

Fabrication of the microcantilevers using the traditional methods is time-consuming and costly. With the advancement of additive manufacturing methods, the fabrication of functional microcantilevers is possible. This work presents the fabrication of elastomeric microcantilevers using the SLA 3D printing technology. Different microcantilevers are fabricated. The mechanical characteristics of the fabricated cantilevers are identified by performing micromechanical tests. Results show that the cantilevers’ measured stiffnesses are comparable with those reported in the literature. The method explained in this work reveals the possibility of employing SLA 3D printing and soft elastomeric printing materials to fabricate microcantilevers.

A method for cleaning flat punch diamond microprobe tips

Microprobe tips are commonly used to perform in-situ micromechanical tests within an electron microscope. In service, such tips have a tendency to accumulate along their surface a layer of deposited material. Tip cleanliness is crucial in order to obtain reliable and reproducible data; however, cleaning of such tips can be arduous, due to their fragility. The literature on appropriate tip cleaning methods is relatively sparse; we aim in this study to fill this gap by presenting an effective way to clean flat punch diamond microprobe tips within an electron microscope, based on mechanical scraping. Initial attempts to remove deposits from a contaminated diamond tip using two micro-brush samples, one containing silica needles and the other containing cementite lamellae, were unsuccessful, due to the adherence of the deposit to the surface of the tip and its apparently high hardness. The successful cleaning method consists of milling a silicon ridge by means of a focused ion beam, and then using this ridge to effectively scrape the deposits off the tip surface in a controlled and complete manner. This method avoids potential damage to the microprobe and can be implemented easily to clean flat punch tips rapidly within a scanning electron microscope.

Biodegradable Thermoplastic Starch/Polycaprolactone Blends with Co-Continuous Morphology Suitable for Local Release of Antibiotics.

We report a reproducible preparation and characterization of highly homogeneous thermoplastic starch/pol(ε-caprolactone) blends (TPS/PCL) with a minimal thermomechanical degradation and co-continuous morphology. These materials would be suitable for biomedical applications, specifically for the local release of antibiotics (ATB) from the TPS phase. The TPS/PCL blends were prepared in the whole concentration range. In agreement with theoretical predictions based on component viscosities, the co-continuous morphology was found for TPS/PCL blends with a composition of 70/30 wt.%. The minimal thermomechanical degradation of the blends was achieved by an optimization of the processing conditions and by keeping processing temperatures as low as possible, because higher temperatures might damage ATB in the final application. The blends’ homogeneity was verified by scanning electron microscopy. The co-continuous morphology was confirmed by submicron-computed tomography. The mechanical performance of the blends was characterized in both microscale (by an instrumented microindentation hardness testing; MHI) and macroscale (by dynamic thermomechanical analysis; DMTA). The elastic moduli of TPS increased ca four times in the TPS/PCL (70/30) blend. The correlations between elastic moduli measured by MHI and DMTA were very strong, which implied that, in the future studies, it would be possible to use just micromechanical testing that does not require large specimens.

Nanostructure and Morphology of the Surface as Well as Micromechanical and Sclerometric Properties of Al2O3 Layers Subjected to Thermo-Chemical Treatment

The article presents the effect of the thermo-chemical treatment of Al2O3 layers on their nanostructure, surface morphology, chemical composition as well as their micromechanical and sclerometric properties. Oxide layers were produced on EN AW-5251 aluminium alloy (AlMg2) by the method of direct current anodizing in a three-component electrolyte. The thermo-chemical treatment was carried out in distilled water and aqueous solutions of Na2SO4·10H2O and Na2Cr2O7·2H2O. It was shown that the thermo-chemical treatment process changes the morphology of the surface of the layers (the formation of a sub-layer from the Na2SO4·10H2O and Na2Cr2O7·2H2O solutions), which directly increases the thickness of the layers by 0.37 and 1.77 µm, respectively. The thermo-chemical treatment in water also resulted in the formation of a 0.63 µm thick sub-layer. The micromechanical tests indicated a rise in the surface microhardness of the layers in the case of their thermo-chemical treatment in water and the Na2SO4·10H2O solution and a decrease in the case of the layers modified in the Na2Cr2O7·2H2O solution. The highest microhardness (7.1 GPa) was exhibited by the layer modified in the Na2SO4·10H2O solution. Scratch tests demonstrated that the thermo-chemically treated layers had better adhesive properties than the reference layer. The best scratch resistance was exhibited by the layer after thermo-chemical treatment in the Na2SO4·10H2O solution (the highest values, practically for all the critical loads) which, together with its low roughness and high load capacity, predispose it to sliding contacts.

Orientation-dependent superelasticity and fatigue of CuAlMn alloy under in situ micromechanical tensile characterization

The in situ micromechanical tensile tests are conducted to characterize the superelastic behaviors for [223], [1214], [325] and [205] oriented Cu67Al24Mn9 micro-slats. The stress-induced martensitic transformations are captured in all textures corresponding to strong crystallographic anisotropy. We propose a one-dimensional constitutive model considering the directional anisotropy of elastic modulus for cubic symmetry and the crystallographic compatibility of twinned martensite. The modeled mechanical behaviors agree with the micromechanical tensile tests well, which suggests that the formation of compatible twins is the primary deformation mechanism. Particularly in the [205] texture, we observed formation of nano-cavities (<100nm) on the lateral surface of the micro-slat. Based on the analysis of compatible martensite twin laminates and fcc slip systems, we theorize that the massive normal elongation and little lateral shear cause the formation, stretching and growth of nano-cavities at nano scales to accommodate the external loads. As a result, the structural and functional fatigue resistance is improved compared to other textures. The experimental and theoretical results in this paper are potentially useful to guide the texture design of Cu-based shape memory alloy for high transformation strain and low functional fatigue.

Optically Pumped Magnetometer Measuring Fatigue-Induced Damage in Steel

Uniaxial fatigue testing of micro-mechanical metallic specimens can provide valuable insight into damage formation. Magnetic and piezomagnetic testing are commonly used for qualitative characterization of damage in ferromagnetic specimens. Sensitive and accurate measurements with magnetic sensors is a key part of such a characterization. This work presents an experimental setup to induce structural defects in a micro-mechanical fatigue test. Simultaneously, the resulting piezomagnetic signals are measured during the complete lifetime of the tested specimen. The key component is a highly sensitive optically pumped magnetometer (OPM) used to measure the piezomagnetic hysteresis of a small specimen whose structural defects can be analyzed on a small scale by other metallographic characterization methods as well. This setup aims to quantify the magnetic signatures of damage during the fatigue process, which could enable non-destructive mechanical testing of materials. This paper reports the initial results obtained from this novel micro-magneto-mechanical test setup for a ferritic steel specimen.