Comparative Transcriptomic Analyses of Different Jujube Cultivars Reveal the Co-Regulation of Multiple Pathways during Fruit Cracking

Fruit cracking is a common physiological disorder in many fruit species. Jujube (Ziziphus jujuba Mill.) is an economically valuable fruit in which fruit cracking seriously affects fruit yield and quality and causes significant economic losses. To elucidate cracking-related molecular mechanisms, the cracking-susceptible cultivars ‘Cuizaohong’ and ‘Jinsixiaozao’ and the cracking-resistant cultivar ‘Muzao’ were selected, and comparative transcriptome analyses of cracking and non-cracking ‘Cuizaohong’ (CC and NC), cracking and non-cracking ‘Jinsixiaozao’ (CJ and NJ), and non-cracking ‘Muzao’ (NM) were conducted. A total of 131 differentially expressed genes (DEGs) were common to the CC vs. NC and CJ vs. NJ comparisons. To avoid passive processes after fruit cracking, we also mainly focused on the 225 gradually downregulated DEGs in the CJ, NJ, and NM samples. The functional annotation of the candidate DEGs revealed that 61 genes related to calcium, the cell wall, the cuticle structure, hormone metabolism, starch/sucrose metabolism, transcription factors, and water transport were highly expressed in cracking fruits. We propose that expression-level changes in these genes might increase the turgor pressure and weaken mechanical properties, ultimately leading to jujube fruit cracking. These results may serve as a rich genetic resource for future investigations on fruit cracking mechanisms in jujube and in other fruit species.

Investigation on the Micromechanisms of the Cracking of 316L Heat Exchanger Tubes

The cracking mechanisms of 316L heat exchanger tubes employed in power station were studied using optical microscope (OM) and scanning electron microscope (SEM). It is demonstrated that the hardness value, microstructure and tensile properties of selected #1 and #2 tube samples all meet the requirements of relevant standards, but the contents of Ni and Mo element of #1 tube are slightly lower than the standard requirements. The circumferential cracks on the two samples nucleate at the corrosion pits on the inner wall of the tubes, while Cl element was detected in the corrosion products of these pits. The cracks propagate from the inner wall to the outer wall along the circumferential direction of the tube, forming a dendritic crack morphology with both transgranular and intergranular propagation characteristics. Combined with the investigation of the service condition of the heat exchanger tubes and the analysis of the experimental results, it can be concluded that the main reason for cracking is the initiation of pin-corrosion when the content of chloride ion exceeds the standard during the service of the tubes, which will induce stress corrosion cracking, causing crack expansion through the wall thickness, and finally lead to leakage of the tube. In addition, from the point of view of materials, Mo is an important element to improve the pitting resistance of materials. The content of Mo element detected in the samples is lower than the standard requirement, which is also one of the reasons for the easy pitting corrosion of the inner wall of the pipe.

Fracture toughness of ABS additively manufactured by FDM process

Purpose: The purpose on this article is to study the failure of FDM printed ABS by exhibiting an exhaustive crack growth analysis mainly based on raster angle parameter. Design/methodology/approach: Two approaches have been developed in this study; On one hand, mechanical experiments were carried out to determine the critical stress intensity factor KIC. On the other hand, numerical analysis was used to predict the paths within the part as well as the crack propagation. Findings: This work has clearly shown the effect of raster angle on the damage mechanism of the ABS printed by FDM. Indeed, for the combination 1 (0°/90°), the structure presents an important stiffness and a high degree of stress distribution symmetry with respect to the notch. Moreover, the crack propagation is regular and straight, and the damage surfaces are on the same plane. However, for the combination 2 (-45°/45°), the structure is less resistant with an asymmetrical stress distribution according to two different planes. Research limitations/implications: In order to present an exhaustive study, we focused on the effect of two raster angles (including 0°/90°, -45°/45°) on the ABS crack propagation, additively manufactured. This study is still in progress for other raster angles, and will be developed from a design of experiments (DoE) design that incorporates all relevant factors. To highlight more the cracking mechanisms, microscopic observations will be developed in more depth. Practical implications: Our analysis can be used as a decision aid in the design of FDM parts. Indeed, we can choose the raster angle that would ensure the desired crack propagation resistance for a functional part. Originality/value: In this article, we have analyzed the mechanism of damage and crack propagation. This topic represents a new orientation for many research papers. For our study, we accompanied our experimental approach with an original numerical approach. In this numerical approach, we were able to mesh distinctly raster by raster for all layers.

Resistance of Austenitic Stainless Steels to Ductility-Dip Cracking: Mechanisms

In Ni-based alloys, precipitates that form along grain boundaries (GBs) during terminal solidification have been shown to pin GBs and resist GB sliding, which can cause ductility-dip cracking (DDC). As a result, it is often suggested that the stainless steel skeletal/lacy  in a  matrix resists DDC because it pins GBs. In the present study, austenitic stainless steels 304, 316, 310, and 321 were quenched with liquid Wood’s metal (75˚C) during welding. Quenching captured the elevated-temperature micro-structure and simultaneously induced cracking, thus revealing the mechanisms of the resistance to DDC. In addition, DDC was much higher in 310 than 304, 316, and 321, which is consistent with results of conventional tests. Both 304 and 316 solidified as columnar  grains, with continuous  formed along GBs soon after solidification to resist DDC along the GBs. 321 solidified as equiaxed grains of  instead of columnar, and the tortuous GBs associated with equiaxed grains resisted DDC. 310, however, solidified as coarse, straight  grains with little  along the GBs, and solidification GBs migrated to become locally straight. The resulting GBs were long, straight, and naked, which is ideal for DDC. In 304, 316, or 321, skeletal/lacy  in a  matrix did not exist in the fusion zone near the mushy zone, where DDC occurs. This proved skeletal/lacy  cannot resist DDC as often suggested. Instead, the present study identified two new mechanisms of resistance to DDC: 1) formation of continuous or nearly continuous  along boundaries of columnar  grains and 2) solidification as equiaxed  grains.