ISO 12135, which provides a fracture toughness test procedure, requires crack front straightness. In order to meet this requirement in weld specimens, Annex C to ISO 15653 provides a local ...compression (LC) technique. Although this technique has been used widely, some interested parties have reported that it often results in excessive underestimation of the critical CTOD. Following these previous studies, the authors reviewed the appropriate LC conditions and presented the typical effects of LC on fracture toughness and crack front straightness in this paper. In this regard, we conducted numerical analysis, sacrificial test, and fracture toughness test and investigated the LC effect on the crack front straightness and fracture toughness. In conclusion, a typical LC with an appropriate platen results in a straight crack front, but also has a large influence on fracture toughness, and it is difficult to solve this problem only by adjusting the amount of LC strain.
The local compression (LC) technique is used to achieve a straight crack front in weld specimens. However, some interested parties have reported that it results in an excessive underestimation of the ...fracture toughness value. In a previous study, the authors investigated an improved LC condition for securing a straight crack front while maintaining the fracture toughness value through a numerical analysis and fracture toughness tests. As a result, it was found that two local compression conditions which do not apply compression at the future notch tip are superior to the typical LC. However, since these proposed conditions were identified based on the experience of the authors, there may be others that will yield better results. In this study, Bayesian optimization was conducted to identify an improved LC condition. Because the results indicated that the compression area and position are important for improving LC, the conditions for a validation experiment were determined based on these parameters. The proposed LC condition achieved a straight crack front, and the fracture toughness was higher than under the condition recommended in ISO 15653. Therefore, the authors concluded that the condition for improvement of LC was successfully identified by the Bayesian optimization.
The local compression technique is used to achieve a straight crack front in weld specimens. However, some interested parties have reported that it decreases the fracture toughness value. The authors ...investigated the better local compression condition for securing a straight crack front while maintaining the fracture toughness value by a numerical analysis, and as a result, some local compression conditions, which do not involve compression of the crack tip, identified as promising. Fracture toughness tests were also conducted with these local compressions, and the test results showed that the fatigue precrack shape and fracture toughness value follows those estimated tendency by the numerical analysis. Two local compression conditions, which compress at the future notch side and ligament side by a square jig and at the ligament side by a circle jig, achieved a straight crack front while maintaining the fracture toughness value. The authors concluded that these new techniques are superior to that recommended in ISO 15,653.
ISO 12135, which describes the method for the fracture toughness test, requires that the specimen temperature be held at the test temperature for 30 s per 1 mm of specimen thickness before testing to ...ensure a constant temperature through the full specimen thickness. However, this requirement results in an inefficient practice when testing thick specimens; e.g., a specimen with a thickness of 100 mm must be held at the test temperature for 50 min. Considering the high thermal conductivity of metals, the authors considered this requirement is excessively conservative, and therefore developed a new decision method for the temperature control time based on a heat transfer analysis. In the proposed method, the temperature control time is decided based on the material properties and temperature condition as well as the specimen thickness, and the required time is much shorter than that required by the ISO standard for general purposes. Cooling tests were conducted to investigate the effectiveness of the proposed method. The temperature history was measured at the surfaces and mid-thickness, and as a result, the proposed method showed more rational required times than the ISO requirement. The proposed required time was overestimated in most tests, however, these errors are significantly smaller than that of conventional one. Although some results were underestimated by a few seconds, this is not a problem because the values were sufficiently small. Based on these results, we concluded that the proposed method is more appropriate than the requirement in the ISO standard.
•Conversion method considering pre-strain direction is proposed.•Fracture toughness tests were performed to investigate pre-strain effect.•Fracture toughness decreases by half or more by 1% LC ...strain.
Previous studies presented the fracture toughness evaluation values decrease due to pre-strain by local compression. However, it was not possible to distinguish whether the cause was fracture toughness deterioration or poor crack front shape straightness due to a bowing crack front at low strain. The authors applied pre-strain without affecting the crack front shape and conducted fracture toughness tests showing that 1% pre-strain reduces fracture toughness by 50%. Furthermore, we investigated the effect of the pre-strain direction on fracture toughness, and proposed a method for converting longitudinal pre-strain to thickness direction strain and demonstrated its effectiveness.
If more than one fracture toughness test is performed for the same material, the representative fracture toughness value is obtained from the minimum of three equivalent (MOTE) in accordance with the ...related standards. MOTE is evaluated by referring to the lowest value of the test results when the number of results is 3 to 5, the second lowest when 6 to 10, and the third lowest when 11 to 15. With the conventional process, it is clear, however, that the value depends on the number of test results. When comparing the MOTE evaluation values with 3 and 5 test results, the MOTE based on 5 results is statistically lower than that with 3 results because both MOTEs refer to the lowest value, while increasing the number of test results from 5 to 6 will increase MOTE because the reference of MOTE changes from the lowest value to the second lowest. However, we are of the view that the number of test results should not affect the evaluation value.Based on the above, we considered two new evaluation methods which are independent of the number of test results, and investigated the effectiveness of those methods by analytical and experimental approaches. As a result, the proposed methods continued to give a constant evaluation value regardless of the number of tests, and the variance was less than that of the conventional method in many cases. Therefore, we concluded that the proposed methods are superior to the conventional method.
Precise integration of individual cell behaviors is indispensable for collective tissue morphogenesis and maintenance of tissue integrity. Organized multicellular behavior is achieved via mechanical ...coupling of individual cellular contractility, mediated by cell adhesion molecules at the cell–cell interface. Conventionally, gene depletion or laser microsurgery has been used for functional analysis of intercellular mechanotransduction. Nevertheless, these methods are insufficient to investigate either the spatiotemporal dynamics or the biomolecular contribution in cell–cell mechanical coupling within collective multicellular behaviors. Herein, we present our effort in adaption of PhoCl for attenuation of cell-to-cell tension transmission mediated by E-cadherin. To release intercellular contractile tension applied on E-cadherin molecules with external light, a genetically encoded photocleavable module called PhoCl was inserted into the intracellular domain of E-cadherin, thereby creating photocleavable cadherin (PC-cadherin). In response to light illumination, the PC-cadherin cleaved into two fragments inside cells, resulting in attenuating mechanotransduction at intercellular junctions in living epithelial cells. Light-induced perturbation of the intercellular tension balance with surrounding cells changed the cell shape in an epithelial cell sheet. The method is expected to enable optical manipulation of force-mediated cell-to-cell communications in various multicellular behaviors, which contributes to a deeper understanding of embryogenesis and oncogenesis.
Mitochondria participate in various metabolic pathways, and their dysregulation results in multiple disorders, including aging-related diseases. However, the metabolic changes and mechanisms of ...mitochondrial disorders are not fully understood. Here, we found that induced pluripotent stem cells (iPSCs) from a patient with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) showed attenuated proliferation and survival when glycolysis was inhibited. These deficits were rescued by taurine administration. Metabolomic analyses showed that the ratio of the reduced (GSH) to oxidized glutathione (GSSG) was decreased; whereas the levels of cysteine, a substrate of GSH, and oxidative stress markers were upregulated in MELAS iPSCs. Taurine normalized these changes, suggesting that MELAS iPSCs were affected by the oxidative stress and taurine reduced its influence. We also analyzed the retinal pigment epithelium (RPE) differentiated from MELAS iPSCs by using a three-dimensional culture system and found that it showed epithelial mesenchymal transition (EMT), which was suppressed by taurine. Therefore, mitochondrial dysfunction caused metabolic changes, accumulation of oxidative stress that depleted GSH, and EMT in the RPE that could be involved in retinal pathogenesis. Because all these phenomena were sensitive to taurine treatment, we conclude that administration of taurine may be a potential new therapeutic approach for mitochondria-related retinal diseases.
Display omitted
•iPS cell lines were derived from a MELAS patient with the mtDNA A3243G mutation.•Decreased proliferation and survival of MELAS iPSCs were rescued by taurine.•Reduction in GSH/GSSG ratio in MELAS iPSCs was suppressed by taurine.•EMT in MELAS iPSC-derived retinal pigment epithelium was suppressed by taurine.•Oxidative stress markers in MELAS iPSCs and RPE were suppressed by taurine.
We prove the stability of the Riemannian curvature dimension condition introduced by Ambrosio–Gigli–Savaré under the concentration of metric measure spaces introduced by Gromov. This is an analogue ...of the result of Funano–Shioya for the curvature dimension condition of Lott–Villani and Sturm. These conditions are synthetic lower Ricci curvature bound for metric measure spaces. En route, we also prove the convergence of the Cheeger energy in our setting.
This paper deals with the optimization of blade stiffened composite panels. The main objective of the research is to make response surfaces for the constraints. The response surface for warping ...thermal deformation was previously made for a fixed dimension composite structure. In this study, the dimensions of the blade stiffener were treated as design variables. This meant that a new response surface technique was required for the constraints. For the response surfaces, the lamination parameters, linear thermal expansions and dimensions of the structures were used as variables. A genetic algorithm was adopted as an optimizer, and an optimal result, which satisfied two constraints, was obtained. As a result, a new response surface was obtained, for predicting warping thermal deformation.
PDF
