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Purpose: Engineering composite laminates/structures are usually subjected to complex and variable loads, which result in interlayer delamination damage. However, damaged laminate may cause the whole structure to fail before reaching the design level. Therefore, the purpose of this paper is to develop an equivalent model to effectively evaluate compressive residual strength. Design/methodology/approach: In this paper, taking carbon fiber reinforced composite T300/69 specimens as the study object, first, the compressive residual strength under different impact energy is obtained. Then, zero-thickness cohesive elements, Hashin failure criteria and Camanho nonlinear degradation scheme are used to simulate the full-process simulation for compression after edge impact (CAEI). Lastly, based on an improved Whitney–Nuismer criterion, the equation of edge hole stress distribution, characteristic length and compressive residual strength is used to verify the correctness of the equivalent model. Findings: An equivalent relationship between the compressive residual strength of damaged laminates and laminates with edge hole is established. For T300/69 laminates with a thickness of 2.4 mm, the compressive residual strength after damage under an impact energy of 3 J is equivalent to that when the hole aperture R = 2.25 mm and the hole aperture R = 9.18 mm when impact energy is 6 J. Besides, the relationship under the same size and different thickness is obtained. Originality/value: The value of this study is to provide a reference for the equivalent behavior of damaged laminates. An equivalent model proposed in this paper will contribute to the research of compressive residual strength and provide a theoretical basis for practical engineering application. [ABSTRACT FROM AUTHOR]

In order to study the influence of the distribution characteristics of micro pores in soil on the strength of foamed soil with river sludge, the digital image analysis method was applied on the qualitative and quantitative analysis of the micro pore distribution in the foamed soil with river sludge. The experimental results show that the pore groups with 0.06-0.08 mm and0.20-0.40 mm equivalent aperture are dominant pore groups in foamed soil with river sludge under laboratory condition, the strength of foamed soil with river sludge is closely related to the distribution characteristics of dominant pore groups; the increase of the foam amount will lead to the increase of the number and area proportion of the larger size pore group, the increase of inhomogeneity of pore size distribution, and the decrease of the strength and stiffness of foamed soil with river sludge; the increase of the cement content makes the number and area proportion of the larger size pore group in the foamed soil with river sludge decrease, and the strength and stiffness of foamed soil with river sludge are improved. [ABSTRACT FROM AUTHOR]

The unfrozen water content is a result of soil freezing, and its variation is closely related to temperature. To study the change in unfrozen water content, a relationship between water pressure and ice pressure is built based on the Clapeyron equation. Then, using an assumption of coincident faces between the water–ice interface and the water–air interface, a formula is deduced to estimate the unfrozen water content via the soil-water potential curve combined with the capillary pressure theory. In this process, the soil particle size distribution curve is introduced to determine the soil pore-size distribution and obtain the soil-water potential curve. Finally, verification and analysis are performed by comparing these results with the pre-existing test data for unfrozen water content. The results show that unfrozen water content can be calculated by means of the soil particle size distribution curve, and the simulation accuracy has a positive correlation with the degree of saturation occupied by water. Moreover, the equivalent aperture size increases as the mean grain size of the soil increases, and the equivalent aperture size increases sharply and approaches the mean particle size when the mean is within a range of relatively large values. Additionally, the value of scale parameter α has an obvious influence on the unfrozen water content curve, as enlargement of α causes an increase in the unfrozen water content and makes water freezing in soils more difficult, and vice versa. [ABSTRACT FROM AUTHOR]

The air voids distribution has a significant effect on the pavement performance related distresses such as rutting, cracking, moisture damage and permeability. However, most studies only quantified the air voids by average content, ignoring the heterogeneity inside the materials. This study focuses on the heterogeneity of air voids distribution inside the open-grade asphalt mixture based on 2D image analysis. Equivalent aperture is proposed to measure the area of each air void. Results showed that along both vertical and horizontal sections inside the open-grade asphalt mixture, the number of voids with 0~2 mm equivalent aperture would have a great impact on the total number of voids, while large amounts of small voids would not significantly affect the total voids number. Additionally, voids with 0~4 mm equivalent aperture account for the largest proportion, and when the equivalent aperture is beyond 4 mm, the number of voids would decrease as the equivalent aperture increases, regardless of the void areas. Furthermore, in both vertical and horizontal sections, as the equivalent aperture increases, the speed to accumulate voids area would firstly increase and then decrease. As the equivalent aperture increases, the contribution to the total voids area would increase accordingly, and it would approach the peak when the equivalent aperture reaches about 8 mm. [ABSTRACT FROM AUTHOR]

The air voids distribution has a significant effect on the pavement performance related distresses such as rutting, cracking, moisture damage and permeability. However, most studies only quantified the air voids by average content, ignoring the heterogeneity inside the materials. This study focuses on the heterogeneity of air voids distribution inside the open-grade asphalt mixture based on 2D image analysis. Equivalent aperture is proposed to measure the area of each air void. Results showed that along both vertical and horizontal sections inside the open-grade asphalt mixture, the number of voids with 0~2 mm equivalent aperture would have a great impact on the total number of voids, while large amounts of small voids would not significantly affect the total voids number. Additionally, voids with 0~4 mm equivalent aperture account for the largest proportion, and when the equivalent aperture is beyond 4 mm, the number of voids would decrease as the equivalent aperture increases, regardless of the void areas. Furthermore, in both vertical and horizontal sections, as the equivalent aperture increases, the speed to accumulate voids area would firstly increase and then decrease. As the equivalent aperture increases, the contribution to the total voids area would increase accordingly, and it would approach the peak when the equivalent aperture reaches about 8 mm.

The first hydraulic stimulation for enhanced geothermal system (EGS) development in Korea had been conducted in the PX-2 well of 4,348 m depth in Pohang EGS site from January 29 th to February 20 th , 2016. Treatment histories of injection rate, wellhead pressure and corresponding induced microseismicity data were obtained from the stimulation test upon 140 m long open hole section at the well bottom. Wellhead pressure was up to 89 MPa and considerable level of flow rate was attempted up to 47 L/sec. Microseismicity observation showed a trend of lager and more frequent seismicity occurrence in shut-in phase than in injection phase. The injectivity index during the stimulation periods had increased as 2.7 times in January 30 th at the wellhead pressure of 73 MPa. Postulating the existence of a major fracture zone intersecting the open hole section, the transmissivity and the corresponding equivalent aperture of the fracture were evaluated. Required breakdown pressures by hydrofracturing and hydroshearing mechanisms were estimated based on the various scenarios on the in-situ stress condition, major fracture zone orientation and shear failure criteria. [ABSTRACT FROM AUTHOR]