Apparent Strain Research Articles

Therapeutic radiation directly alters bone fatigue strength and microdamage accumulation

Radiotherapy (RTx) is an essential and efficacious oncologic treatment, however, post-RTx bone fragility fractures present a challenging clinical problem. Cancer survivors treated with RTx are at variable risk for these late-onset, complex fragility fractures. Little data exists regarding the effects of RTx on bone fatigue properties despite the likelihood of fatigue loading as a mechanism leading up to atraumatic fracture. In this study, femurs collected from adult male rats were irradiated ex vivo with a therapeutic dose of x-irradiation (20 Gy), and then fatigued using a three-point bend setup. Femurs positioned in an isotonic bath at room temperature were loaded to a range of prescribed initial strain levels (based on beam theory equations, prior to any fatigue damage) at 3 Hz in force control. The goals of this study were to determine the feasibility of assessing RTx-induced alterations in 1) femur fatigue strength, 2) structural microdamage (creep and stiffness), and 3) tissue damage (diffuse damage and/or linear microcracking). Mid-diaphyseal morphology and tissue mineral density were not different between the RTx and Sham groups (p ≥ 0.35). With increasing applied apparent strain, the number of cycles to failure was reduced for the RTx femurs when compared to the Sham femurs (treatment x εapp, p = 0.041). RTx femurs had a greater phase II (steady state) creep rate (p = 0.0462) compared to Sham femurs. For femurs that reached 500k cycles, the RTx group had greater diffuse damage area (p = 0.015) than the Sham. This study provides evidence that radiation at therapeutic doses can directly diminish bone fatigue properties. This loss of fatigue properties is associated with increased structural fatigue damage and diffuse microdamage, without alterations in morphology or tissue mineral density, indicating a reduction in bone quality.

Evaluation of compression behaviour of 316L SS Gyroid and Diamond structures using SLM process – Experimental programme under static and dynamic compression loadings

The relative comparison in terms of energy absorption efficiency for a set of 4 structures made of various Triply Periodic Minimal Surfaces (TPMS) topologies is experimentally investigated. These TPMS structures are printed by Selective Laser Melting AM process using 316L SS. The study is carried out in consideration of the effect of parameters such as relative density, compressive loading directions and loading rates, number of unit cells for Diamond and Gyroids TPMS both declined for Sheet and Skeletal topologies. The objective is to quantify their structural responses in terms of apparent stress and strain, dynamic enhancement and Specific Energy Absorbed (SEA) and to evaluate their structural integrity in terms of collapse stability. The results reveal that the Sheet pattern of TPMS structures with its constant wall thickness and uniform geometry exhibits better energy absorption capabilities than the Skeletal pattern. The Diamond family shows greater interest rather than the Gyroid family only in the case of the Sheet pattern. The increase in relative density from 20 to 30% is characterized by improved manufacturing quality, an increase in energy absorption capacity and more homogeneous progressive deformations during compression. On the whole, the set of TPMS geometries exhibits energy absorption capacities prior to those of other conventional cellular materials currently used for impact engineering applications. Finally, in a first approach, an original design methodology using charts can be developed to establish a link between the energy absorption capabilities and the design geometric parameters of TPMS structures.

Excipient-Induced Lattice Disorder inActive Pharmaceutical Ingredient: Implications on Drug Product Continuous Manufacturing.

Our previous work (Mol Pharm, 20 (2023) 3427) showed that crystalline excipients, specifically anhydrous dibasic calcium phosphate (DCPA), facilitated the dehydration of carbamazepine dihydrate (CBZDH) and the formation of an amorphous product phase during the mixing stage of continuous tablet manufacturing. Understanding the mechanism of this excipient-induced effect was the object of this study. Blending with DCPA for 15 min caused pronounced lattice disorder in CBZDH. This was evident from the 190% increase in the apparent lattice strain determined by the Williamson-Hall plot. The rapid dehydration was attributed to the increased reactivity of CBZDH caused by this lattice disorder. Lattice disorder in CBZDH was induced by a second method, cryomilling it with DCPA. The dehydration was accelerated in the milled sample. Annealing the cryomilled sample reversed the effect, thus confirming the effect of lattice disorder on the dehydration kinetics. The hardness of DCPA appeared to be responsible for the disordering effect. DCPA exhibited a similar effect in other hydrates, thereby revealing that the effect was not unique to CBZDH. However, its magnitude varied on a case-by-case basis. The high shear powder mixing was necessary for rapid and efficient powder mixing during continuous drug product manufacturing. The mechanical stress imposed on the CBZDH, and exacerbated by DCPA, caused this unexpected destabilization.

Damage deformation properties and acoustic emission characteristics of hard-brittle rock under constant amplitude cyclic loading

In order to study the deformation and damage characteristics of the limestone specimens with high strength and brittleness under constant amplitude cyclic loading, the deformation and the acoustic emission (AE) characteristics were analysed, and the relationship between them was sought. The damage variables under different amplitude cyclic loading were defined by AE counts. The results showed that the radial deformation of the limestone specimens was more sensitive and unstable than the axial deformation. The concept of apparent residual strain was proposed to describe the specimen deformation characteristics, and it resulted that the radial apparent residual strain produced at higher stress state would recover at lower stress state. The limestone specimens showed obvious Kaiser effect and Felicity effect under cyclic loading. When the upper limit of the cyclic loading was close to the peak stress of the specimen, the AE counts generated in unloading sections were almost the same as that in the loading sections. The damage was increased as the amplitude and the stress level increased and the unloading process at higher stress level would also lead to the aggravation of damages. Specimens would absorb more energy under cyclic loading than under uniaxial loading. Reasonable driving parameters should be controlled in underground excavation practice, to ensure that the stress level of surrounding rock mass in a periodic stress state is located before peak stress and such that to limit the occurrence of rock burst to a certain extent.

3D regional evaluation of right ventricular myocardial work from cineCT.

Regional myocardial work (MW) is not measured in the right ventricle (RV) due to a lack of high spatial resolution regional strain (RS) estimates throughout the ventricle. We present a cineCT-based approach to evaluate regional RV performance and demonstrate its ability to phenotype three complex populations: end-stage LV failure (HF), chronic thromboembolic pulmonary hypertension (CTEPH), and repaired tetralogy of Fallot (rTOF). 49 patients (19 HF, 11 CTEPH, 19 rTOF) underwent cineCT and right heart catheterization (RHC). RS was estimated from full-cycle ECG-gated cineCT and combined with RHC pressure waveforms to create regional pressure-strain loops; endocardial MW was measured as the loop area. Detailed, 3D mapping of RS and MW enabled spatial visualization of strain and work strength, and phenotyping of patients. HF patients demonstrated more overall impaired strain and work compared to the CTEPH and rTOF cohorts. For example, the HF patients had more akinetic areas (median: 9%) than CTEPH (median: <1%, p=0.02) and rTOF (median: 1%, p<0.01) and performed more low work (median: 69%) than the rTOF cohort (median: 38%, p<0.01). The CTEPH cohort had more impairment in the septal wall; <1% of the free wall and 16% of the septal wall performed negative work. The rTOF cohort demonstrated a wide distribution of strain and work, ranging from hypokinetic to hyperkinetic strain and low to medium-high work. Impaired strain (-0.15≤RS) and negative work were strongly-to-very strongly correlated with RVEF (R=-0.89, p<0.01; R=-0.70, p<0.01 respectively), while impaired work (MW≤5 mmHg) was moderately correlated with RVEF (R=-0.53, p<0.01). Regional RV MW maps can be derived from clinical CT and RHC studies and can provide patient-specific phenotyping of RV function in complex heart disease patients. Evaluating regional variations in right ventricular (RV) performance can be challenging, particularly in patients with significant impairments due to the need for 3D spatial coverage with high spatial resolution. ECG-gated cineCT can fully visualize the RV and be used to quantify regional strain with high spatial resolution. However, strain is influenced by loading conditions. Myocardial work (MW) - measured clinically derived as the ventricular pressure-strain loop area - is considered a more comprehensive metric due to its independence of preload and afterload. In this study, we sought to develop regional RV myocardial work (MW) assessments in 3D with high spatial resolution by combining cineCT-derived regional strain with RV pressure waveforms from right heart catheterization (RHC). We developed our method using data from three clinical cohorts who routinely undergo cineCT and RHC: patients in heart failure, patients with chronic thromboembolic pulmonary hypertension, and adults with repaired tetralogy of Fallot.We demonstrate that regional strain and work provide different perspectives on RV performance. While strain can be used to evaluate apparent function, similar profiles of RV strain can lead to different MW estimates. Specifically, MW integrates apparent strain with measures of afterload, and timing information helps to account for dyssynchrony. As a result, CT-based assessment of RV MW appears to be a useful new metric for the care of patients with dysfunction.

Mandrel diameter effect on ring-pull testing of nuclear fuel cladding

Inconsistencies in ring-pull testing methods for thin-walled tubes make it difficult to compare a material's mechanical properties in the hoop direction presented in past publications. The effect of test setup, specifically mandrel diameter, was investigated for nuclear fuel cladding tubes of the iron-chromium-aluminium (FeCrAl) alloy, C26M (Fe-12Cr-6Al-2Mo). Mandrel diameter for ring-pull testing can change how the ring deforms and friction effects, further convoluting the results from testing. To address the impact of mandrel size in relation to ring diameter, gaugeless ring-pull samples were tested across a range of mandrel diameters and compared to uniaxial tensile tests from the same tube of material. Two groups of samples were tested: an as-received, low ductility sample set and an annealed, high ductility sample set, both cut from the same extruded tube. By pairing systematic variation of mandrel geometry with analysis of local strain gradients using digital image correlation, this study investigates the effect of test fixture geometry on apparent mechanical properties and effective strain fields and provides guidance for comparing previously published data. Certain features in uniaxial stress-strain curves (namely the yield strength, ultimate tensile strength, and uniform elongation) appeared to have analogies in the effective stress-strain curves from ring-pull testing. These corresponding features are compared to expose biases in the analysis of material properties using gaugeless ring-pull and to provide novel guidance on test setup during experimental design.

Experimental study on the impact of “IDS + JFCS” complex wetting agent on the characteristics of coal bodies

As China's coal mines have transitioned to deep mining, the ground stress within the coal seams has progressively increased, resulting in reduced permeability and poor wetting ability of conventional wetting agents. Consequently, these agents have become inadequate in fulfilling the requirements for preventing washouts during deep mining operations. In response to the aforementioned challenges, a solution was proposed to address the issues by formulating a composite wetting agent. This composite wetting agent combines a conventional surfactant with a chelating agent called tetrasodium iminodisuccinate (IDS). By conducting a meticulous screening of surfactant monomer solutions, the ideal formulation for the composite wetting agent was determined by combining the monomer surfactant with IDS. Extensive testing, encompassing evaluations of the composite solution's apparent strain, contact angle measurements, and alterations in the oxygenated functional groups on the coal surface, led to the identification of the optimal composition. This composition consisted of IDS serving as the chelating agent and fatty alcohol polyoxyethylene ether (JFCS).Subsequent assessment of the physical and mechanical performance of the coal briquettes treated with the composite wetting agent revealed notable enhancements. These findings signify significant advancements in the field and hold promising implications. Following the application of the composite wetting agent, notable reductions were observed in the dry basis ash and dry basis full sulfur of coal. Additionally, the water content within the coal mass increased significantly, leading to a substantial enhancement in the wetting effect of the coal body. This enhanced wetting effect effectively mitigated the coal body’s inclination towards impact, thereby offering technical support for optimizing water injection into coal seams and preventing as well as treating impact ground pressure.

Transient Response of Macroscopic Deformation of Magnetoactive Elastomeric Cylinders in Uniform Magnetic Fields.

Significant deformations of bodies made from compliant magnetoactive elastomers (MAE) in magnetic fields make these materials promising for applications in magnetically controlled actuators for soft robotics. Reported experimental research in this context was devoted to the behaviour in the quasi-static magnetic field, but the transient dynamics are of great practical importance. This paper presents an experimental study of the transient response of apparent longitudinal and transverse strains of a family of isotropic and anisotropic MAE cylinders with six different aspect ratios in time-varying uniform magnetic fields. The time dependence of the magnetic field has a trapezoidal form, where the rate of both legs is varied between 52 and 757 kA/(s·m) and the maximum magnetic field takes three values between 153 and 505 kA/m. It is proposed to introduce four characteristic times: two for the delay of the transient response during increasing and decreasing magnetic field, as well as two for rise and fall times. To facilitate the comparison between different magnetic field rates, these characteristic times are further normalized on the rise time of the magnetic field ramp. The dependence of the normalized characteristic times on the aspect ratio, the magnetic field slew rate, maximum magnetic field values, initial internal structure (isotropic versus anisotropic specimens) and weight fraction of the soft-magnetic filler are obtained and discussed in detail. The normalized magnetostrictive hysteresis loop is introduced, and used to explain why the normalized delay times vary with changing experimental parameters.

Crack Coalescence Mechanism and Crack Type Determination Model Based on the Analysis of Specimen Apparent Strain Field Data

Crack Coalescence Mechanism and Crack Type Determination Model Based on the Analysis of Specimen Apparent Strain Field Data

Multiscale mechanical characterisation of the craniofacial system under external forces

Premature fusion of craniofacial joints, i.e. sutures, is a major clinical condition. This condition affects children and often requires numerous invasive surgeries to correct. Minimally invasive external loading of the skull has shown some success in achieving therapeutic effects in a mouse model of this condition, promising a new non-invasive treatment approach. However, our fundamental understanding of the level of deformation that such loading has induced across the sutures, leading to the effects observed is severely limited, yet crucial for its scalability. We carried out a series of multiscale characterisations of the loading effects on normal and craniosynostotic mice, in a series of in vivo and ex vivo studies. This involved developing a custom loading setup as well as software for its control and a novel in situ CT strain estimation approach following the principles of digital volume correlation. Our findings highlight that this treatment may disrupt bone formation across the sutures through plastic deformation of the treated suture. The level of permanent deformations observed across the coronal suture after loading corresponded well with the apparent strain that was estimated. This work provides invaluable insight into the level of mechanical forces that may prevent early fusion of cranial joints during the minimally invasive treatment cycle and will help the clinical translation of the treatment approach to humans.

Hierarchical Flower-like Sulfides with Increased Entropy for Electromagnetic Wave Absorption.

The concept of high entropy is considered promising to enhance electromagnetic wave absorption properties. However, preparing high-entropy sulfides with unique structures for high-performance electromagnetic absorption remains a challenge. In this study, hierarchical porous flower-like dual-phase sulfides were designed with increased entropy and fabricated using a versatile approach. The porous flower configuration enhanced the scattering of electromagnetic waves and the impedance-matching characteristics. Additionally, the effect of high entropy induced diverse defects that were favorable for electromagnetic wave dissipation in dual-phase sulfides. The design of the dual-phase structure generated strong interface polarization, and the composition and content of the phases exhibited clear changes with the increase in the number of metal elements. Interestingly, apparent lattice distortions, defects, and shear strains were directly observed near the dual-phase interface of millerite (102) and pyrite (220) planes, facilitating the occurrence of dipole polarization. Consequently, the developed dual-phase high-entropy sulfide exhibited outstanding microwave absorption properties. The minimum reflection loss value of (FeCoNiCuZn)S was -45.8 dB at a thickness of 1.5 mm, and the optimal effective absorption bandwidth was 3.8 GHz at a thickness of 1.4 mm thickness. Thus, the design of high-entropy sulfides brings meaningful guidance for tuning the wave absorption properties in sulfides.

Nanoscale engineering of low-misfit TiB2/Al3(Sc,Zr)/α-Al multi-interface to improve strength-ductility synergy for direct energy deposited aluminum alloy

The nature of the interface between ceramic particle (CP) and metal matrix is critical to obtain solidification microstructures with optimal mechanical properties of CP-reinforced Al alloys in additive manufacturing. Generally, when the lattice misfit between the CP (e.g., TiB2) and the α-Al matrix is higher than 4%, the interfacial coherency reduces, lowering the effectiveness of CPs. Here, we demonstrate that an L12 three-dimensional compound (3DC), which possesses lattice misfit with α-Al lower than 1%, can be introduced in between TiB2 and α-Al via properly regulating the solidification cooling rate. In the 5TiB2/Al-4.5Mg-0.7Sc-0.2Zr (wt%) as a model system, the lattice coherence of the TiB2/α-Al interface is tailored by introducing a 10–30 nm thick Al3(Sc,Zr) 3DC interphase when the cooling rate is increased to ∼1000 °C/s. But, further increasing the cooling rate to ∼6800 °C/s, only Al3(Sc,Zr) two-dimensional compound (2DC) with an apparent lattice strain forms at the interface. Taking advantage of the cooling rate (102-103 oC/s) provided by laser direct energy deposition (L-DED), the low-misfit “TiB2/Al3(Sc,Zr) 3DC/α-Al” multi-structural interfaces are acquired, enabling the 3.56TiB2/Al-4.36Mg-0.72Sc-0.22Zr alloy as fabricated with L-DED to achieved improved strength-ductility synergy (yield strength 257 MPa, elongation 13.8%) due to the isotropically fine Al grain structure and the homogenous TiB2 particle dispersion. The outcome of this study provides fundamental knowledge on designing “ceramic/coherent primary interphase/metal matrix” multi-structural interfaces to improve the mechanical properties of engineering metallic materials manufactured by rapid solidification techniques, such as DED additive manufacturing (AM).

Effects of polypropylene fibers and aggregate contents on the impact performance of coral aggregate concrete

The paper aims to study the effect of polypropylene (PP) fibers and aggregate contents on the impact compression mechanical performance of coral aggregate concrete (CASC). 5 PP fiber contents (0 kg/m3, 1 kg/m3, 2 kg/m3 3 kg/m3, 4 kg/m3), 3 natural gravel replacement ratios (0 %, 40 %,70 %), and 3 impact pressures (0.10 MPa, 0.12 MPa, 0.14 MPa) were designed for the split Hopkinson pressure bar (SHPB) test herein. The PP fiber contents and gravel replacement ratios effects on the impact compressive properties of CASC were assessed in term of the stress-strain curve, the strain rate effects and the toughness. The results showed that the dynamic compressive strength enhanced obviously with the increasing PP fiber contents and gravel replacement ratio, while the excessive fiber can degrade its properties instead. There exists the apparent strain rate effect of dynamic compressive strength and dynamic increase factor. The addition of PP fiber and the gravel can also improve the toughness of CASC and weaken the strain rate sensitivity. Eventually, the dynamic constitutive model based on ZWT constitutive model was established by considering the material damage, which can excellently forecast the dynamic stress-strain curve of CASC and the dynamic mechanical properties.

Creep behavior of sandstone under the coupling action of stress and pore water pressure using three-dimensional digital image correlation

Understanding the damage evolution and time-dependent property of rock creep is of great significance for predicting geohazards and evaluating the long-term stability of geotechnical structures. In this study, a three-dimensional digital image correlation system was adopted to investigate the creep behavior of sandstone under the coupling action of stress and pore water pressure. The apparent strain fields, deformation characteristics of the localization zone, and micromorphology of the fracture surface were analyzed. The results demonstrated that when the applied deviatoric stress level was above σci (crack initial stress) or σcd (crack damage stress), the increase in pore water pressure promoted creep deformation evidently, improved the creep rate significantly and shortened the time-to-failure of the rock obviously. In the radial strain field, the localized development of substantial microcracks on the rock surface was concentrated in the steady-state creep, while the microcracks interconnected to form macroscopic shear cracks that dominated the accelerating creep, and this damage evolution characteristic can be used as a precursor and early warning of rock creep failure. Besides, increasing the pore water pressure also would cause the divergence point of strain curves inside and outside the localization zone to appear earlier at the secondary creep, and produce a wider localization zone at the tertiary creep. The creep fracture surface of the rock was dominated by intergranular microcracks. Increasing the pore water pressure would result in the deterioration of the cemented structure and breakage of the cemented matrix more seriously, thus stimulating the generation of more microcracks.

Glacial-isostatic-adjustment strain rate–stress paradox in the Western Alps and impact on active faults and seismicity

Abstract. In many regions formerly glaciated during the Last Glacial Maximum (LGM), glacial isostatic adjustment (GIA) explains most of the measured uplift and deformation rates. GIA is also proposed as a key process contributing to fault activity and seismicity shortly after the LGM and potentially up to the present day. Here, we study the impact of GIA on present-day fault activity and seismicity in the Western Alps. We show that, in the upper crust, GIA induces horizontal compressive stress perturbations associated with horizontal extension rates. The latter agree with the observed geodetic strain rates and with the seismicity deformation patterns. Yet, in nearly all cases, the GIA stress perturbations tend to either inhibit fault slip or promote fault slip with the wrong mechanism compared to the seismicity deformation style. Thus, although GIA from the LGM explains a major part of the Western Alp geodetic strain rates, it does not drive or promote the observed seismicity (which must be driven by other processes). This apparent strain rate–stress paradox results from the gradual diminution over time of the finite shortening induced in the upper crust by the Würm ice cap load. A direct corollary of our results is that seismicity and seismic-hazard studies in the Western Alps cannot directly integrate geodetic velocities and strain rates but instead require detailed modeling of the GIA transient impact.

Creep-dominated fatigue of freestanding gold thin films studied by bulge testing

Although metallic thin films are widely used in microelectronics, their high-cycle fatigue properties are not well-understood. Cyclic testing was conducted on 150-nm thick freestanding gold thin films using nominal stress amplitudes between 50 and 150 MPa at 23–100 °C. As expected, lifetime decreases with increasing stress amplitude and temperature. The strain at failure hardly exceeds 1.5%, which is in agreement with previous studies on metallic thin films. The hysteresis stress-strain curves suggest that strain accumulates mostly due to cyclic creep. Based on this observation, we calculated the stress exponent n and activation energy Q – which are typical creep parameters – from the apparent steady-state strain rate observed during cyclic testing. Comparison to preexisting creep bulge tests show that the higher the temperature, the more pronounced the influence of creep on the fatigue behavior. Especially at 100 °C, creep mechanisms clearly dominate. At lower temperatures (23 °C) the data indicate that creep still plays a role, but intrinsic cycling effects become more pronounced. That leads us to postulate that the fatigue lifetime of gold thin films is closely connected to their creep properties.

Unraveling Seed Dormancy and Host Specificity of Alectra Vogelii in Malawi

Parasitic angiosperm Alectra vogelii Benth is a growing problem in Malawi, particularly with the current emphasis on legume crops. Therefore, a pot experiment was conducted in Lilongwe, Malawi to evaluate the effects of site, A. vogelii dormancy-breaking period on Mkanakaufiti and IT82E-16 cowpea varieties. Varieties of cowpea were grown in A. vogelii-infested pots sourced from three agroecological zones and subjected to varied dormancy-breaking periods. The experiment was arranged in a Randomized Complete Block Design and replicated four times. The study revealed that dormancy breaking had impacts depending on the A. vogelii source. However, the Alectra source affected the A. vogelii shoot counts and cowpea grain weight. Neno-Manyenye collections had a higher incidence without induced dormancy breaking periods while Lilongwe-Kamowa, and Salima-Matumba collections had a high incidence after the dormancy-breaking period. Late infestation (at 119 to 149 days after planting) on resistant Mkanakaufiti cowpea variety by A. vogelii collections used indicated apparent strain variability of collections used. The results confirmed the delayed resistance mechanism of Mkanakaufiti against A. vogelii. Nevertheless, the variety reactions on the parasitic weed depends on suitability, compatibility, and specificity, although some resistant genotypes tend to lose the resistance mechanism with time. A. vogelii seeds organic carbon % varied (4.87±1.73 to 9.13±0.95) from the three agroecological zones which signified the collections’ variability due to warmer temperatures, relative humidity, and crop husbandry practices under long-term conditions. Therefore, screening efforts for resistance or evaluation of agronomic options to suppress the weed should be intensified.

Температурна характеристика електричного опору тензометра при вимірюванні статичних та термічних напружень деталей при температурі до 700 °С

An overview of the existing methods of measuring static stresses at elevated temperatures, at which it is problematic to use classical strain gauges, and methods of compensating the imaginary temperature deformation was performed. Namely: the use of multi-component alloys, the manufacture of active and compensatory sensitive elements from different alloys, which should theoretically compensate for each other's shortcomings. In practice, this can be sufficiently achieved only in a narrow temperature range. The described primary transducer is a rectangular strain-gauge rosette for measuring static and thermal stresses in structural parts operating under extreme conditions at temperatures up to 700°C. This sensor is a two-layer rosette consisting of two sensitive elements (SE), the main axes of which are rotated relative to each other by 90°. The lower SE perceives the main deformation of the part, and the upper one, located above the lower one, plays the role of a temperature-compensating electrical resistance of the element and simultaneously registers the transverse deformation of the part. SE rosettes were made of a wire with a diameter of 30 microns of the Х20Н80 alloy and fixed to each other and to the part using Ц-165-32А cement. The experimental study consisted in determining the temperature characteristics of the resistance of both the lower and the upper SE of the studied strain gauge associated with the temperature expansion of the part-strain gauge system as well as with the shunting of the insulator-connector and the change in the specific resistance of the SE material. Experimental determination of apparent strain gauge deformation at different temperatures was performed. To determine the influence of the coefficient of linear expansion of the material of the part on the change in the resistance of the SE, strain gauges were attached to samples of various materials. The change in the apparent deformation of the strain gauge in the temperature range from room temperature to 700 °C is shown. Its maximum value for the ceramic sample was less than 350 µm/m, for the 30ХГСА steel sample it was less than 1000 µm/m, and for the ВЖЛ14Н-ВІ alloy sample it was less than 750 µm/m. Dependencies were obtained that allow corrections to be made in the result of a real study of the stressed state of the part to achieve the maximum accuracy of measurements.

Influence of distributed out-of-plane waviness defects on the mechanical behavior of CFRP laminates

One of the most common defects induced during manufacturing of laminates is out-of-plane fibre waviness. This defect significantly affects the mechanical behavior of the laminate and reduces fatigue life and the load capacity of the material. Therefore, it is important to understand the impact of fibre waviness on the performance of composite laminates. In this work, multiple out-of-plane waves have been introduced throughout a Carbon Fibre Reinforced Polymer (CFRP) laminate at different thickness positions. The specimens were tested under tensile loading and an analysis of the surface of the laminate has been carried out by means of Digital Image Correlation (DIC). The results obtained by DIC were able to predict the apparent strain of the laminate quite accurately, as well as locate up to seven undulations at different depths. It was proved that a laminate with multiple wrinkles has 16% less tensile load strength. The results were used to validate different Finite Element (FE) models of the laminate showing a good agreement. These simple models were able to predict the initiation and propagation of failure in both the matrix and the fibre.

A Comparative Study on the Dynamic Tensile Strength Evaluation Method of Rock Materials

The representative calculation methods of dynamic tensile strength applied to the spalling test are comparatively reviewed in the same experimental cases. The results are compared with those of the ISRM suggested dynamic BD method. Through comparative verification results and analysis of methodological characteristics of each determination method in the spalling test, the most reasonable method for calculating dynamic tensile strength in the high strain rate condition is derived. The local strain rate and apparent strain rate are calculated for the same experimental cases, and the difference in the result values according to the strain rate calculation technique is analyzed through comparative verification of the calculated results. Consequently, the characteristics of each dynamic tensile strength determination method and strain rate calculation method in the spalling test are presented, and the results of the review on the most suitable method for calculating the dynamic tensile strength of rock materials are presented.