Estimation of C* Integral for Mismatched Welded Compact Tension Specimen

The C* integral for the compact tension (CT) specimen is calculated using the estimation equation in ASTM E1457-15. This equation was developed based on the assumption of material homogeneity and is not applicable to a welded CT specimen. In this paper, a modified equation for estimating the C* integral for a welded compact tension (CT) specimen under creep conditions is proposed. The proposed equation is defined on the basis of systematically conducted extensive finite element (FE) analyses using the ABAQUS program. A crack in the welded CT specimen is located in the center of the heat-affected zone (HAZ), because the most severe type IV cracks are located in the HAZ. The results obtained by the analysis show that the equation for estimating the C* integral in ASTM E1457-15 can underestimate the value of the C* integral for creep-soft HAZ and overestimate for creep-hard HAZ. Therefore, the proposed modified equation is suitable for describing the creep crack growth (CCG) of welded specimens.

Heterogeneous Tissue Modulus Improved Prediction of Mechanical Behavior in Osteoporotic Vertebral Cancellous Bone

The structural integrity of cancellous bone, which is essential to skeletal load-bearing capacity, is governed chiefly by apparent density, trabecular architecture, and tissue material properties. Metabolic bone disorders such as osteoporosis can affect each of these factors separately, resulting in compromised load-bearing function. While the impact of apparent density and architecture on bone mechanical behavior has been well-documented, much less is known about the influence of tissue material properties, particularly in osteoporotic bone. The goal of the present study is to isolate the influence of tissue material properties on the pre-yield mechanical response of normal and osteoporotic cancellous bone to uniaxial compression using finite element (FE) models derived from 3D micro-computed tomography images. Both average tissue material properties and the degree of tissue material heterogeneity vary between individuals. Therefore, three sets of FE models were created to study the relative importance of these two factors: 1) models with material homogeneity within and between subjects, 2) models with material homogeneity within subjects only, and 3) models with material heterogeneity within and between subjects. The results of finite element analyses were compared to data gathered from physical testing with matched conditions. For normal bone, incorporating material heterogeneity within and between subjects had no significant effect on model performance. For osteoporotic bone, incorporating material heterogeneity within subjects did not affect model performance, but models that incorporated subject-specific average material properties were significantly more accurate in replicating the results of physical testing. We conclude that, while the influence of bone apparent density and trabecular architecture on apparent stiffness are dominant in healthy bone, average material properties also play a role in osteoporotic bone. Osteoporosis is diagnosed based on apparent density alone, so our findings suggest a need to consider other patient-specific differences that may affect average tissue material properties, such a bone remodeling rate, in clinical assessments of osteoporotic bone structural integrity.

Corrosion Behavior of Cold Sprayed Aluminum Alloys 2024 and 7075 in an Immersed Seawater Environment

This paper describes the polarization and basic pitting behavior of 2024 and 7075 aluminum alloys produced by high pressure cold spray deposition. While cold spray is showing great promise as a solid state repair approach for metallic structures, the corrosion behavior of these materials still needs investigation, particularly in describing the potential galvanic interactions with the repaired substrate. Potentiodynamic testing was performed on cold sprayed (CS) aluminum alloys 2024 and 7075, and corresponding wrought AA2024-T3 and AA7075-T651 alloys for comparison. Testing used ASTM D1141 artificial seawater for potentiodynamic polarization, following the MIL-STD 889C standard for testing with consistent results. Pitting was investigated using 120-hour immersion tests, with subsequent photography, SEM imaging and EDS analysis of the surface. CS-2024 was found to be more active and reactive than wrought, with enhanced anodic kinetics; it experienced more aggressive pitting than the AA2024-T3 during the immersion test. CS-7075 was found to be less active and more reactive than wrought, with enhanced cathodic kinetics; the CS-7075 demonstrated reduced pitting compared to the AA7075-T651. Possible causes for these differences are discussed, including material homogeneity, CS powder intermetallics, and spray parameters. Overall, CS-2024 and CS-7075 should have little galvanic interaction with their corresponding substrates.

MECHANICAL CHARACTERISTICS OF THE MATERIAL OF ADDITIVE STRUCTURES WITH DIFFERENT METHODS FOR DETERMINING THE CROSS-SECTION AREA OF SPECIMENS

В статье рассматривается вопрос определения механических характеристик материала аддитивных структур с учетом таких параметров печати, как процент заполнения и направление нитей печати. В исследованиях использовались три типоразмера стандартизированных образцов на центральное растяжение, изготовленных с применением технологии 3D-печати. В ходе экспериментов было установлено, что при определении механических характеристик материала необходимо отходить от гипотезы однородности и сплошности материала, принятой в сопротивлении материалов. Для определения значений механических характеристик у образцов разных типоразмеров была предложена методика по расчету реальной площади поперечного сечения исследуемой структуры. В статье приведены диаграммы растяжения и рассчитанные по ним механические характеристики материала аддитивных структур, а также рассмотрен вопрос влияния отношения площади структуры к площади ограждения на механические характеристики материала. The article discusses the issue of determining the mechanical characteristics of the material of additive structures, taking into account such printing parameters as the percentage of filling and the direction of the printing filaments. The studies used three sizes of standardized specimens for central tension, made using 3D printing technology. During the experiments, it was found that when determining the mechanical characteristics of a material, it is necessary to deviate from the hypothesis of material homogeneity and continuity, adopted in the strength of materials. To determine the values of mechanical characteristics for samples of different sizes, a technique was proposed for calculating the real cross-sectional area of the structure under study. The article presents tensile diagrams and the mechanical characteristics of the material of additive structures calculated from them, as well as the issue of the influence of the ratio of the structure area to the perimeter area on the mechanical characteristics of the material.

Development of color guides to evaluate the maturity of cacao clones by digital image processing

ABSTRACT Raw material homogeneity is one of the most requested characteristics in any production industry, and the cacao industry is no exception. However, there are many factors that affect the final quality of fruits, among them the variety and maturity stage. The present study aimed to create color tables for evaluating the maturity index of the ICS06, CCN51 and EET8 cacao clones, using digital image processing, in order to contribute for the quality and final homogeneity of the fruits and their by-products.

Criticality Hidden in Acoustic Emissions and in Changing Electrical Resistance during Fracture of Rocks and Cement-Based Materials

Acoustic emissions (AE) due to microcracking in solid materials permit the monitoring of fracture processes and the study of failure dynamics. As an alternative method of integrity assessment, measurements of electrical resistance can be used as well. In the literature, however, many studies connect the notion of criticality with AE originating from the fracture, but not with the changes in the electrical properties of materials. In order to further investigate the possible critical behavior of fracture processes in rocks and cement-based materials, we apply natural time (NT) analysis to the time series of AE and resistance measurements, recorded during fracture experiments on cement mortar (CM) and Luserna stone (LS) specimens. The NT analysis indicates that criticality in terms of electrical resistance changes systematically precedes AE criticality for all investigated specimens. The observed greater unpredictability of the CM fracture behavior with respect to LS could be ascribed to the different degree of material homogeneity, since LS (heterogeneous material) expectedly offers more abundant and more easily identifiable fracture precursors than CM (homogenous material). Non-uniqueness of the critical point by varying the detection threshold of cracking events is apparently due to finite size effects which introduce deviations from the self-similarity.

Enhanced Direct Dimethyl Ether Synthesis from CO2-Rich Syngas with Cu/ZnO/ZrO2 Catalysts Prepared by Continuous Co-Precipitation

The manufacturing of technical catalysts generally involves a sequence of different process steps, of which co-precipitation is one of the most important. In this study, we investigate how continuous co-precipitation influences the properties of Cu/ZnO/ZrO2 (CZZ) catalysts and their application in the direct synthesis of dimethyl ether (DME) from CO2/CO/H2 feeds. We compare material characteristics investigated by means of XRF, XRD, N2 physisorption, H2-TPR, N2O-RFC, TEM and EDXS as well as the catalytic properties to those of CZZ catalysts prepared by a semi-batch co-precipitation method. Ultra-fast mixing in continuous co-precipitation results in high BET and copper surface areas as well as in improved metal dispersion. DME synthesis performed in combination with a ferrierite-type co-catalyst shows correspondingly improved productivity for CZZ catalysts prepared by the continuous co-precipitation method, using CO2-rich as well as CO-rich syngas feeds. Our continuous co-precipitation approach allows for improved material homogeneity due to faster and more homogeneous solid formation. The so-called “chemical memory” stamped during initial co-precipitation is kept through all process steps and is reflected in the final catalytic properties. Furthermore, our continuous co-precipitation approach may be easily scaled-up to industrial production rates by numbering-up. Hence, we believe that our approach represents a promising contribution to improve catalysts for direct DME synthesis.