This paper considers a detailed mechanism of the electrical resistance change observed after delamination cracking of a thin Carbon Fiber Reinforced Polymer (CFRP) laminate. For this laminate, the electrical resistance increases after delamination cracking, although the electrical resistance decreases after delamination cracking of a thick CFRP laminate. One of the proposed reasons for this difference is the residual strain relief caused by the delamination cracking. We report experimental and FEM analyses to investigate the effect of shut-off of the current path caused by delamination cracking, and the effect of piezoresistance caused by residual strain relief after delamination cracking. Residual strain relief was measured experimentally, and the results compared to the FEM results. On the basis of the FEM results the effect of the piezoresistance was estimated. It was found that the effect of the piezoresistance is small compared to the effect of the current shut-off for the thin CFRP laminate.

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Based on a two-dimensional physical model of a mode I crack with a slip band, the analysis of mechanical interaction between hydrogen and dynamic dislocations with non-steady emission from a stressed source around a crack tip is conducted. To analyze the mechanical interaction between a crack and dynamic dislocations on a neighboring slip band, a crack is replaced by static discrete dislocations mechanically equivalent with the crack and a physical model of analyzing the mechanical interaction between static, dynamic dislocations and hydrogen is constructed. The occurrence conditions of the mechanisms of corrosive anodic chemical reaction, inter-granular cracking due to hydrogen concentration and facet like fracture due to the interaction between hydrogen and dynamic dislocations were clarified. These results were found to be in good agreement with previous results based on a convenient one-dimensional model. Furthermore, the competitive interaction between hydrogen and dynamic dislocations which causes the facet like fracture is found to occur under the limited velocity range of hydrogen and dynamic dislocations which is closely related to the corresponding range of yield stress.

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Printed wiring board (PWB) for mobile devices continues to have higher wiring density and more complicated structures from functionality requirements in addition to product size restriction. With enhancing the functionality, PWB failures occurred by drop impact is one of the most critical stresses to mobile devices. This paper illustrates the influences of the PWB in the detailed structures level “micro-scale structures” over drop reliability. The micro-scale structures studied include microvias, dielectric layers and copper layers. In order to characterize those influences, board-level drop tests and 2-dimensional mechanical simulation in micro-scale were conducted. It was clarified that the micro-scale structures had significant influences to drop reliability, and also the effectiveness of micro-scale approach was verified.

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Ratcheting behavior has been investigated on Inconel 718 at 649°C under axial-torsional loading with load control. Ratcheting strain was measured to near failure cycles. The effects of loading path, magnitude of stress amplitude and mean stress on the development of ratcheting strain over the life have been studied by comparing the equivalent ratcheting strain. Ratcheting strain is found to increase with cycles in the manner similar to the creep strain under static load. Ratcheting rates are found higher for circular paths than for linear paths. More ratcheting occurs when the cyclic stress and mean stress are in the same direction. No clear relation is found between the ratcheting strain at failure and fatigue life, however fatigue life decreases as the ratcheting rate increases under the same applied stress.

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In this paper, the use of silver nanoparticles paste has been proposed to laser-weld AZ31B magnesium alloy with a thickness of 0.3 mm. The paste containing Ag nanoparticles of 5 nm in average diameter and an organic solvent was used to coat the surface of AZ31B thin sheet by a spin coater. The coated sheet was heated at 100 °C for 60 s to evaporate the solvent. The dried sheet was set as a lower AZ31B sheet on the jig, and then lap fillet welding was carried out by using a pulsed Nd:YAG laser in a closed box filled with argon gas. Characteristics of microstructure and mechanical properties of the joint were investigated. When the Ag nanoparticles paste was used, parameters for welding the thin AZ31B sheet were identified: a pulse energy of 1.8 J, pulse duration 3.0 ms, pulse repetition rate 80 Hz, and scan speed between 7.5 mm/s (450 mm/min) to 10.8 mm/s (650 mm/min). Under these conditions, the bond width improves, defects reduce and process parameters range broadens compared to welding without using the paste. Besides, the area of high hardness widens due to the increase of the fine grain area and the decrease of the heat affected zone. Weld joint efficiency also improves up to 92 % of the base metal.

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Fiber waviness is one of the initial defects in the filament winding process, and causes reduction of compressive strength of the composite structure. The mechanism of growth of fiber waviness is, however, not completely clear. In the present study, a model for generating fiber waviness is proposed. It is assumed to be due to local fiber micro-buckling arising from the compression load caused by shrinkage of a metal jig. Three faults are considered as causes of micro-buckling: bonding between metal jig and composite, insufficient cure of the resin, and initial deflection of fibers. Analysis and experiments based on this model have been carried out.

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The creep damage condition of components under elevated temperature is a requirement to guarantee safe life extension and continued operation. Destructive and/or non-destructive assessments are regularly applied to assess the remaining life of components during service. Uniaxial creep specimens have been traditionally employed for conventional tests to examine a series of high temperature creep properties. However the ability to remove these relatively large uniaxial specimens is limited due to the required size of the specimens with respect to the component dimensions. To overcome this shortcoming, small element testing techniques such as miniature creep (MC) and small punch creep (SPC) tests have recently been proposed to investigate creep properties. However their applications are limited as there is no established standard for the testing procedures and subsequent data evaluation. In order to aid the standardization of the SPC test method, this paper investigated the deformation and fracture of interrupted SPC tests. Results showed that the creep deformation in the SPC test could be classified into three conventional stages. Firstly, the crack of about 1mm in the diameter developed on the extended surface of the disc specimen at the end of the primary creep stage. Secondly, during secondary creep, circumferential cracking progressed in the through-thickness direction by about 0.1mm. Lastly, the tertiary creep region was extremely short and only appeared just before final fracture and failure. The result showed that the ratio of load in the SPC test to stress in the uniaxial creep proposed past was smaller than the experiment value. This result was due to the early crack formation in the disc specimen and the shear type crack development, and the difference of loading ball's diameter.

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