Peak Load Energy Research Articles

Effect of multiple holes on dynamic buckling of stubby shells: An experimental and numerical investigation

Current study investigates the deformation behavior and energy absorption of thin walled cylinders having multiple holes when subjected to dynamic compressive loading. A split-Hopkinson pressure bar (SHPB) was utilized for obtaining short duration dynamic loading. A SIM02-16 high speed camera was employed to capture the real time images of the deformation process. Holes of different diameters were arranged in different geometric configurations along the length of the cylinders. The effect of holes and their arrangement on peak load reduction and energy absorption characteristics of the cylinders was investigated. From the experimental study, it was observed that the diameter of the holes, their spacing, and pattern of arrangement, all have a strong influence on the peak load transmitted by the cylinders and also on the deformation pattern. Larger number of smaller diameter holes resulted in higher peak load reduction. Subsequently a numerical analysis was carried out using the commercially available finite element package Abaqus Explicit 6.11. The results of the analysis revealed that both the level of stress concentration induced by the holes and the interaction of stresses between adjacent holes have a role to play in reducing the peak load through controlling the deformation.

Benefits of Short Kevlar Fiber Reinforcement at the Interface for Repair of Concrete-Like Materials

AbstractInterfacial adhesive bonding of concrete-like materials is strengthened by short Kevlar fibers. The tough and flexible Kevlar fibers, bridging across grain structures, can effectively suppress premature surface and subsurface local fracture at the interface during the formation of fictitious crack. The adhesive joint, formed through either repairing of a gap using epoxy or structural reinforcement using carbon-fibers/epoxy composite, is changed into a composite adhesive joint because of use of Kevlar fibers at the interface. In this study, grey granite samples were tested under three-point-bending with two different interfacial repair conditions: (1) epoxy only, and (2) epoxy with short Kevlar fibers of 6 mm in length. Peak loads and RILEM fracture energy Gf were measured from as-received granite samples, and the two different types of repaired samples. Improvements were observed in both the peak load and fracture energy. Formation of fictitious crack and its influence on the peak load were discussed.

Dissimilar ultrasonic spot welding of aerospace aluminum alloy AA2139 to titanium alloy TiAl6V4

The microstructure, hardness, lap shear strength and fracture energy of AA2139–TiAl6V4 spot joints produced by ultrasonic welding were investigated and related to the weld thermal cycle. No obvious intermetallic reaction layer was observed in the AA2139–TiAl6V4 welds, even using transmission electron microscopy. The hardness profile of AA2139 side after welding was studied, demonstrating that the heat introduced by the welding process leads to some softening with partial hardness recovery after natural aging. The effects of welding time on peak load and fracture energy were investigated. The peak load and fracture energy of welds increased with an increase in welding time and then reached a plateau, i.e., maximum peak load 5.3kN and maximum fracture energy 3.7kNmm. In all cases, failure occurred by fracture at the weld interface.

Thermal System Analysis and Optimization of Large-Scale Compressed Air Energy Storage (CAES)

As an important solution to issues regarding peak load and renewable energy resources on grids, large-scale compressed air energy storage (CAES) power generation technology has recently become a popular research topic in the area of large-scale industrial energy storage. At present, the combination of high-expansion ratio turbines with advanced gas turbine technology is an important breakthrough in energy storage technology. In this study, a new gas turbine power generation system is coupled with current CAES technology. Moreover, a thermodynamic cycle system is optimized by calculating for the parameters of a thermodynamic system. Results show that the thermal efficiency of the new system increases by at least 5% over that of the existing system.

Microstructural and mechanical performance of aluminium to steel high power ultrasonic spot welding

Welding of Aluminium 6111-T4 to bare and two different zinc coated steels was successfully carried out using high power ultrasonic spot welding. The thermal behaviour and non-uniform heat distribution at the local weld area were investigated. The effect of heat generation on precipitates dissolution and natural aging of Al6111-T4 was studied. The maximum hardness in TMAZ was 10-15Hv higher than natural aging which is because of higher rate of precipitation due to reduction in grain/subgrain size. The performance of soft hot-dipped DX56-Z and hard galvannealed DX53-ZF zinc coated steels was discussed in terms of mechanical properties and joinability, in comparison with uncoated steel. The highest peak load (3.25kN) and fracture energy (∼5kNmm) was reached in the case of aluminium to hot dipped DX56-Z zinc coated steel joints owing to the maximum ductility. In contrast, in aluminium to galvannealed DX53-ZF zinc coated steel joints failure was promoted earlier with low mechanical properties of 2.6kN shear strength and 1.25kNmm fracture energy as a result of damage to the zinc layer. Formation of brittle Al–Fe intermetallic layer at the interface of aluminium to bare steel was the main effect of reduction in ∼3.0kN lap shear strength at the maxima. Surface damage due to sonotrode welding tip penetration was seen to be more severe in aluminium to bare DC04 steel compared to other weld combinations that resulted strength loss when the thickness of the weld nugget is reduced at the optimum condition.

Microstructure, flexural properties and durability of coir fibre reinforced concrete beams externally strengthened with flax FRP composites

This study investigated the flexural behaviour of plain concrete (PC) and coir fibre reinforced concrete (CFRC) beams externally strengthened by flax fabric reinforced epoxy polymer (FFRP) composites. PC and CFRC beams without and with FFRP (i.e. 2, 4 and 6 layers) reinforcement were tested under three- and four-point bending. The microstructures of coir fibre, coir/cement matrix, flax/epoxy matrix, and FFRP/concrete interfaces were analysed using scanning electronic microscope (SEM). Test results indicated that the peak load, flexural strength, deflection and fracture energy of both PC and CFRC specimens enhanced proportional to an increase of FFRP layers. Coir further increased load, strength and energy of the specimens remarkably. It was also found that the thickness and coir influenced the failure modes while the test method influenced the load and energy of the specimens remarkably. SEM studies showed effective bond at coir/cement, flax/epoxy and FFRP/concrete interfaces. Therefore, it concluded that natural FFRP composites can be used to repair or retrofit existing concrete structures.

Investigation of Microstructure and Mechanical Properties of Resistance Spot Welded Dissimilar Joints Between Ferritic Stainless Steel and Weathering Steel

Resistance spot welding is widely used in automobile and rail car manufacturing industries. In this research work, resistance spot welded dissimilar joints of ferritic stainless steel and weathering steel sheets is investigated for mechanical and metallurgical properties. Ferritic stainless steel AISI 409M and weathering steel corten A (ASTM A 242) of 2mm thickness were used in this work. Spot welding was done at different current values, keeping other parameters such as electrode force, electrode tip diameter and weld time as constant. Test specimens were subjected to tensile shear test and micro hardness test to assess the mechanical properties of the weld joints. The influence of welding current on nugget growth, fusion zone hardness, peak load, and failure energy and failure mode during tensile shear test, was investigated at various current ratings. The results showed that, with increasing value of current, peak load increased correspondingly. Nugget shape was found to be near symmetrical. Nugget diameter was found to be increasing with increase in current, in expulsion free welds. Interfacial mode of failure was noticed at low current values, whereas, at higher current values, pull out mode of failure was observed. Presence of martensite was observed in the fusion zone. Micro hardness values at fusion zone were found to be more than that of both heat affected zones and base metals.

Plain concrete cylinders and beams externally strengthened with natural flax fabric reinforced epoxy composites

The use of bio-composites as construction and building materials will be beneficial for the development of sustainable construction industry. This study evaluated the performance of natural flax fabric reinforced epoxy polymer (FFRP) composites as external strengthening materials for concrete elements. A total of 24 plain concrete cylinders and beams with and without FFRP reinforcement were tested under uni-axial compression and four-point bending. The considered FFRP thicknesses were 2, 4 and 6 layers of the fabric. Microstructures of flax/epoxy and FFRP/concrete interfaces were analysed by scanning electronic microscope (SEM). Test results indicate that in axial compression, FFRP as external strengthening material enhanced peak strength, strain, fracture energy and ductility of the concrete cylinders remarkably, i.e. the increase in strength and fracture energy by 6-layer FFRP is 134 and 2570 %, respectively. Experimental peak strength of the strengthened specimens were compared with the predictions by existing strength equations. A strength equation was proposed to predict the ultimate compressive strength accurately. In flexure, FFRP strengthening increased lateral load, deflection, flexural strength and fracture energy of the concrete beams significantly, i.e. the increase in peak load and fracture energy by 6-layer FFRP is 374 and 4660 %, respectively. SEM studies showed the good interfacial bond between FFRP and concrete because of the epoxy adhesive. The study therefore concluded that the woven FFRP composite is a suitable material for external strengthening of concrete structures.

Experimental investigation into dynamic axial impact responses of double hat shaped CFRP tubes

This paper aims to explore the dynamic responses and crashing characteristics of double hat shaped tubes made of weave carbon fiber reinforced plastic (CFRP). Experimental investigations were carried out into three different thicknesses and lengths of the composite tubes fabricated by the bladder molding process. Three distinct failure modes, classified as progressive end crushing, mid-length collapse and overlap opening, were observed in the dynamic crushing tests. Unlike continuous splaying fronds observed in the quasi-static tests, dynamic tests exhibited a number of fragment segments in the progressive end crushing mode. It is shown that the ply number was a critical parameter affecting the failure mode and energy absorption capability. The increase in ply number led to increases in the peak load and specific energy absorption (SEA); whereas the tubal length seemed insensitive to energy absorption capability. Compared to the quasi-static cases, the dynamic impact tests resulted in the higher peak load (increased from 46 % to 125 %) and lower SEA (reduced from 21 % to 33 %) for the tested tubes.

Modeling peak load reduction and energy consumption enabled by an integrated thermal energy and water storage system for residential air conditioning systems in Austin, Texas

This paper discusses the development of a model for evaluating peak load reduction and change in overall energy consumption for a residential air conditioning (AC) compressor with and without condenser-side thermal storage. Stored rainwater (or any other type of on-site water storage) could be utilized as a heat sink for the condenser during peak hours, allowing for more efficient and lower power compressor operation, then re-chilled at night during off-peak hours. The system evaluated in this manuscript is referred to as ‘integrated thermal energy and rainwater storage’ (ITHERST).The model used simulated cooling load data for a typical home in Austin, Texas, based on summer 2011 historical and typical meteorological year (TMY) datasets. The analysis suggests that the ITHERST system with 3785–18,925l of water could reduce on-peak compressor power demand by approximately 29–53%, as compared to a traditional AC with an air-cooled condenser. However, total compressor energy consumption increases 5–15% because of the inefficiencies of re-cooling the thermal mass, but this additional energy consumption occurs during low demand off-peak hours. System performance varied depending on weather data, the individual compressor, and thermal storage volume.

Impact response of nano reinforced mat glass/epoxy laminates

The present work intends to characterize the effect that nanoclay and carbon nanotubes matrix reinforcements have on low velocity impact response of epoxy/glass fiber composites. The composite matrix used was the epoxy resin Biresin® CR120 combined with the hardener CH120-3 and the fiberglass triaxial mats ETXT 450. The results of the present paper are discussed in terms of load-time, load-displacement, energy-time diagrams and damage. The incorporation of nanoparticles produces only small improvement of the impact response in terms of the peak load and specific recovery energy. Peak load decreases slightly with increasing percentage of nanoparticles reaching a maximum decrease of 6 % for 3 wt% of nanoclays. Specific recovery energy increases in comparison with control formulation, around 14–18 % for 0.5 wt% addition of nanotubes and 7–15 % for 1 wt% of nanoclays, respectively. Specific recovery energy tends to decrease for higher percentages of nanoparticles in consequence of its poor distribution. Damaged area apparent shows a small reduction with nanoparticle content.

Microstructural characterization and mechanical properties of high power ultrasonic spot welded aluminum alloy AA6111–TiAl6V4 dissimilar joints

Aluminum alloy AA6111 and TiAl6V4 dissimilar alloys were successfully welded by high power ultrasonic spot welding. No visible intermetallic reaction layer was detected in as-welded AA6111/TiAl6V4 welds, even when transmission electron microscopy was used. The effects of welding time and natural aging on peak load and fracture energy were investigated. The peak load and fracture energy of welds increased with an increase in welding time and then reached a plateau. The lap shear strength (peak load) can reach the same level as that of similar Al–Al joints. After natural aging, the fracture mode of welds transferred from ductile fracture of the softened aluminum to interfacial failure due to the strength recovery of AA6111.

Modeling the impact of integrating solar thermal systems and heat pumps for domestic hot water in electric systems – The case study of Corvo Island

The use of solar thermal systems with electricity backup and heat pumps as hot water suppliers in residential buildings seems to be a very promising way to increase energy efficiency. Nevertheless, the massive adoption of such solutions in small networks (neighborhood, village) may induce problems in the electric grid management. This study explores the impact of such systems in small electric grids, using an hourly electricity backup load model. To test and validate the model, we used the island of Corvo (Azores), a small isolated community where it is being implemented a project of electrification of domestic hot water systems (DHW). We consider different load scenarios to manage the backup of DHW systems and analyze its consequences on the peak load and overall energy demand. For Corvo, for the best case where the backup is limited and distributed along off-peak hours, we observed an increase of 24% in the peak load and 7.5% in the annual energy demand. Critical values of peak load are found in winter, when daily solar irradiation is lower than 2000 Wh/m2/day. We conclude that the solar thermal systems are responsible for most of the peak load increase, but since they have the flexibility to adjust the electric backup hours due to the thermal storage capacity, the use of these systems can minimize the impact on the grid. Heat pumps on the other hand, albeit being more efficient in terms electric backup, are less flexible to contribute to the grid management as they operate continuously.

Quasi-static axial crushing and transverse bending of double hat shaped CFRP tubes

This paper aims to explore the failure modes and crashworthiness characteristics of double hat shaped tubes made of weave carbon fiber reinforced plastic (CFRP) subjected to quasi-static axial crushing and transverse bending. Experimental investigations were carried out into three different thicknesses of the composite tubes fabricated by the bladder molding process. Three distinct failure modes, classified as progressive end crushing (I), unstable local buckling (II) and mid-length collapse (III), were observed in the axial crushing tests, whereas only one similar progressive collapse mode was observed in transverse bending tests. It is shown that the thickness is a critical parameter affecting the failure mode and energy absorption capability, leading to the increase in the peak load and specific energy absorption (SEA) during the tests. The SEA of the tested double hat shaped tubes under axial crushing ranges from 60 to 90J/g, which is marginally higher than that of regular sectional CFRP tubes but over 2 times of that of conventional metallic tubes. By comparison, the load bearing and energy absorption capabilities of the tubes under transverse bending are much lower than those of the axially compressed tubes (less than 10% and 1%, respectively).

Influence of the Cross Section Shape on Energy Absorbing Component of Bumper Subjected to Low Speed Crash

Energy absorbing component of bumper equipped at the front end of a car, is one of the most important automotive parts for crash energy absorption. It usually was made a mental thin walled tube. In the paper, automobile energy absorbing component at low-velocity impact was studied by using Finite Element Method. The FE model of the tube was builded by comparing the five cross section shape . Results show that the impact peak load and maximum energy absorption have certain effect to energy-absorbing component with different the cross section shape.

Impact properties of glass-fiber/polypropylene composites: The influence of fiber loading, specimen geometry and test temperature

Glass fiber reinforced polypropylene composites were compounded with a twin-screw extruder and injection molded. Fiber length distribution study showed that more fiber degradation occurred during processing of the composites with higher fiber loading. Dynamic mechanical analysis carried out showed that magnitudes of storage and loss modulus of composites are improves with the presence of the glass fiber in the system. The incorporation of fibers into the composites has slightly shifted the glass transition temperature to lower values. On the other hand, the presence of the glass fiber reduces the magnitude of tan δ at α-transition dramatically due to the strengthening effect by the fibers. From impact test, it was found that increment in glass fiber loading leads to an increase in peak load, critical strain energy release rate and critical stress intensity factor indicating the improvement in the material toughness. However, there was no significant change observed in fracture energy. With respect to increasing in specimen geometry, despite an improvement in peak load and fracture energy of the impact specimen, the critical strain energy release rate and critical stress intensity factor values were decreased. On the other hand, increase in test temperature resulted in reduction of peak load and critical stress intensity factor due to increment in material ductility, whereby fracture energy and critical strain energy release rate improved.

Permanent indentation and damage creation of laminates with different composite systems: An experimental investigation

Quasi‐static indentation (QSI) and low‐velocity impact tests have been conducted to laminated composite specimens made from different composite systems. C‐scan and thermal deply techniques were used to observe the internal damage characteristics of the laminates. The test results show the effect of fibers and matrices on the permanent indentation and damage behaviors of composite laminates. Fiber breakage plays an important role in the formation of permanent indentation and the match between the fiber and matrix also has a significant influence on the permanent indentation and damage behaviors. A comparison shows the correlation between the peak load energy of the QSI tests and the knee point energy of the impact tests, based on which a condition for the prominent indentation formation was proposed for the impact tests. POLYM. COMPOS., 35:872–883, 2014. © 2013 Society of Plastics Engineers

Energy Impacts of Nonlinear Behavior of Phase Change Materials When Applied to Opaque Building Envelopes

Research on phase change materials (PCM) as a potential technology to reduce peak loads and heating, ventilation and air conditioning (HVAC) energy use in buildings has been conducted for several decades, resulting in a great deal of literature on PCM properties, temperature, and peak reduction potential. However, there are few building energy simulation programs that include PCM modeling features, and very few of these have been validated. Additionally, there is no previous research that indicates the level of accuracy when modeling PCMs from a building energy simulation perspective. This study analyzes the effects a nonlinear enthalpy profile has on thermal performance and expected energy benefits for PCM-enhanced insulation. The impact of accurately modeling realistic, nonlinear enthalpy profiles for PCMs versus simpler profiles is analyzed based on peak load reduction and energy savings using the conduction finite difference (CondFD) algorithm in EnergyPlus. The PCM and CondFD models used in this study have been previously validated after intensive verification and validation done at the National Renewable Energy Laboratory. Overall, the results of this study show annual energy savings are not very sensitive to the linearization of enthalpy curve. However, hourly analysis shows that if simpler linear profiles are used, users should try to specify a melting range covering roughly 80% of the latent heat; otherwise, hourly results can differ by up to 20%.

Static and low-velocity impact on mechanical behaviors of foam sandwiched composites with different ply angles face sheets

The current studies give a brief account of analysis of static and low-velocity impact on foam sandwiched composites comprising composite faces from carbon/epoxy and cores from Rohacell (polymethacrylimide). The face sheets consist of four different stacking sequences as unidirectional, cross-ply, angle-ply and quasi-isotropic, which were fabricated by using hand lay-up process. Later, the composite panels were subjected to quasi-static and low-velocity impact loading using MTS and an instrumented Drop-Weight Machine (Instron 9250HV), respectively. The load-displacement curves have been obtained to characterize the failure mechanisms in the face sheets and the core. Impact parameters were evaluated and compared for different types of sandwich structures. Failure modes were studied by sectioning the samples at the impact location and observing under optical microscope. The results evaluated from static test have shown that the unidirectional have the highest peak load. However, the dynamic test data indicated that the foam sandwich with unidirectional face sheet have lowest peak load, lowest displacement at peak load and minimum energy absorption. It has also been observed that largest damage size, highest penetration depth and shear cracking have been experienced by unidirectional as compared to cross-ply, angle-ply and quasi-isotropic face sheets.

Mitigation measures for fish habitat improvement in Alpine rivers affected by hydropower operations

ABSTRACTIn mountainous areas, high‐head‐storage hydropower plants produce peak load energy. The resulting unsteady water release to rivers, called hydropeaking, alters the natural flow regime. Mitigating the adverse impacts of hydropeaking on aquatic ecosystems has become a crucial step in recent water policies.We developed a novel economic‐ecological diagnostic and intervention method to assess hydropeaking mitigation measures for fish habitat improvement. This method was applied to an Alpine river downstream of a complex storage hydropower scheme. The approach comprises (1) a hydropower operation model of flow regime generation and cost estimates for different mitigation measures, (2) a two‐dimensional hydrodynamic model to simulate the flow conditions in representative river reaches and (3) a dynamic fish habitat simulation tool to assess the sub‐daily changes in habitat conditions of three brown trout (Salmo trutta fario) life stages (adult, spawning and young‐of‐the‐year). Simulations showed that operational measures such as limiting maximum turbine discharge, increasing residual flow and limiting drawdown range incur high costs in relation to their ecological effectiveness. Compensation basins and powerhouse outflow deviation achieved the best cost–benefit ratio. Hydropeaking impact was strongly dependent on river morphology. Monotonous river reaches exhibited low habitat suitability for peak discharge, whereas a braided morphology provided high in‐stream structure and thus suitable habitat for unsteady flow conditions.The interdisciplinary approach to economic and habitat rating informs decision makers regarding the effectiveness of measures implemented to mitigate the environmental impacts associated with fluctuating hydropower operations. Copyright © 2013 John Wiley & Sons, Ltd.