Polyurethane Foam Composites Reinforced with Renewable Fillers for Cryogenic Insulation

Sawdust, microcellulose and nanocellulose and their silanized forms were used to reinforce rigid polyurethane (PU) foam composites. The concentration of fillers was varied in the range of 0.5–1.5%. For rigid PU foam formulations, three polyols from recycled and renewable materials were used, among other components. Polyols were obtained from rapeseed oil, tall oil fatty acids and recycled polyethylene terephthalate. As rigid PU foam composites in literature have been described as appropriate thermal insulation material, the appliance of obtained composites for cryogenic insulation was investigated by determining the various physical-mechanical properties of composites. The physical-mechanical properties, such as the modulus of elasticity, compressive and tensile strength in both 293 K and 77 K, adhesion measurements with and without cryo-shock, apparent density, thermal conductivity coefficient, and safety coefficient were measured. The results showed that the addition of fillers did not give a significant improvement of characteristics.

OPTIMUM WORKHOLDING CONDITIONS FOR PRECISION CYLINDRICAL GRINDING OPERATIONS

Grinding process is a very important process in machining industry being one of the most popular processes when high quality parts must be manufacture. Likewise, workholding is a critical issue on cylindrical grinding. The use of the driving dog is common when the workpiece is held between centers. However, one of the handicaps of this workholding is that the cylindrical workpiece cannot be ground along the complete length. In order to tackle this issue, in the present work the workpiece is held between centers avoiding the use of the driving dog. To this end, a methodology to obtain the grinding limit parameters that ensure that the transmitted torque is higher that the resistance torque is presented, being the aim of these tests is to avoid the sliding between the point and the workpiece. Finally, non-destructive tests are designed, which, using a safety coefficient of about 0.77, the tests allow the correct design of each specific grinding process. Keywords: cylindrical grinding, workholding, driving dog, sliding

KAJIAN STRUKTUR CHECK DAM 3 BATANG HULU KURANJI KOTA PADANG STUDY OF CHECK DAM STRUCTURE 3 BATANG HULU KURANJI PADANG CITY

Batang Kuranji is a river located in Kota Padang. The high rainfall and human factors that cause changes in characteristics, especially in the upstream area make the water from the flow of kuranji stems in the rainy season often overflows, and cause flash floods, therefore built Check Dam at the head of the river batang kuranji to prevent the shallowing of the riverbed. Thisresearch aims toreview the structure of the Check Dam 3 building on Batang Kuranji in the city of Padang. This study refers to SNI 2851:2015 with rainfall data for 15 years used from 2005 to 2019, with batu busuk observation station and rice fields obtained from PSDA. Luas DAS is obtained from ArcGIS Applications. Dari hydroligi analysis obtained rainfall plan (R100th) 153,152 m3/dt with Gumbel method, Discharge flood plan for the 100 year anniversary period used Haspers method obtained (Q100th) 165.19 m3/dt. The type of Check Dam that is planned is the type of pelimpah (head work) with a height of Check Dam 8.5 m. Tilt of the body at the upstream 0.6, the distance between the main dam and sub dam 25.2 m, the thickness of the apron floor 1.6 m, with an estimated volume of sediment flow that can be accommodated by 14797.6 m3. The stability of the Check Dam construction was obtained at a value of 3.43 >1.5 and a sliding of 1.53 > 1.5 with a safety coefficient of 1.5, so that the construction of the Check Dam was stable.

A Study of Safety Coefficient Determination and Support Parameter Optimization Based on Vulnerability Preevaluation

The preevaluation to the vulnerability of the surrounding rocks is proposed as one of the reliable indicators of the safety coefficient of gateway support and a foundation to optimize the support design parameters. In this study, taking the surrounding rocks, stress, geological environment, and service time into consideration, the safety coefficient is determined based on the vulnerability scores calculated by the vulnerability preevaluation model of the surrounding rock. Applying the safety coefficient to the instability evaluation of the composite rock-bolt bearing structure, the strength required to maintain the stability of the gateway is calculated, which further provides references and guidance to the optimization of the anchor support parameters. This method has been successfully adopted by the GuCheng coal mining project in N1303 tailgate to strengthen the anchor-bolt structure in the roof watering area especially the main inclined shaft. Applying more accurately calculated strength to the anchor-bolt structure can effectively avoid the issue of overcompensation, thus reducing the cost and increasing the driving speed. Furthermore, this method provides insights into optimizing design parameters of the gateway. This method provides a reliable basis for the optimization design of bolt support parameters in coal mine gateway.

Comparison of Existing Equations for the Design of Crown Walls: Application to the Case Study of Ericeira Breakwater (Portugal)

The correct calculation of forces and moments caused by wave action over crown wall structures is critical for their design. There are several existing equations for this, some of which are sanctioned in practice as it is the case for Jensen (1984) and Bradbury et al. (1998), Günback and Gökce (1984), Martin et al. (1999), Berenguer and Baonza (2006), and Pedersen (1996) and Nørgaard et al. (2013). These equations are the main tool for the design of breakwater crown walls and their accuracy is crucial to ensure the stability of the crown wall, especially when considering the sea level rise due to climate change and the possible damage of the armor, since both aspects are not usually considered in most original design studies. In a scenario of climate change, it is very important to estimate the possible changes in security factors due to both these aspects, comparing the results with the original design ones. This paper has as main objective to analyze it for the case study of Ericeira rubble mound breakwater in Portugal. For this, a comparison of the results using those equations and different scenarios including the current, considering sea level rise and armor damage, were performed to extract some conclusions: the increase in the sea level in the case study was not significant and therefore its incidence is very small; and the damage to the main armor by losing pieces at the berm is much more important in this case study, so it is essential to carry out the proper maintenance of the design section. On the other hand, horizontal forces are more conservative using Pedersen and Nørgaard equations, obtaining the lowest value with Martin. Regarding uplift pressures, Martin gives the lowest value, while the most conservative values are given by Günbak and Gökce’s for two scenarios, and Pedersen and Nørgaard for the other two scenarios. Furthermore, the sliding safety coefficient is more conditioning than overturning the safety coefficient in all the scenarios.

Numerical simulation of slope stability of the abandoned dreg site

A mathematical model of No. 1 abandoned dreg site of the newly-built highway from Xiangle village, Pingyao County to Hougou village, Qinyuan County was developed using GeoStudio software. The stability of the abandoned dreg site was simulated and analyzed under rainstorm. As a result, the influence of rainfall infiltration on slope seepage field is not limited to the rainfall process. The slope stability coefficient decreases significantly during the rainfall and the decreases slightly after the rainfall stopped due to continuous rainwater seepage. The minimum safety coefficient is 2.292 at 24h, greater than the allowable value, which demonstrates that the slope is stable.

Experimental and finite element analysis of slope stability treated by lime milk (case of El Amir Abdelkader embankment)

This paper presents an experimental stabilization approach of the landslide that threatens a slope located near the city of El Amir Abdelkader, Ain Temouchent, Algeria. Stabilization is assured by the addition of lime milk, and then a numerical validation of the results with respect to the safety coefficient before and after treatment was performed by “Plaxis” software. Experimental results show that the stabilization by lime milk improves compaction parameters, swelling and shear strength, particularly the cohesion and friction angle, the latter permitting appreciation of the sliding surface on which it is necessary to base the calculation of the safety coefficient before and after treatment. Numerical results indicate that the factor of safety increases with the improvement of the mechanical characteristics c and ϕ, which are improved by increasing lime milk percentage. The numerical validation using “Plaxis” finite element code gives results that are in perfect agreement with the experimental ones, indicating that this software is a good tool for slope stability study.