Load-time Curves Research Articles

Low Velocity Impact of Filament-Wound Glass-Fiber Reinforced Composite Pipes

Low velocity single-bounce impact tests have been conducted on filament-wound glass fiber reinforced/vinylester and glass fiber reinforced/epoxy composite pipes. An instrumented drop weight testing system was used for the impact testing. The tests were performed on 300 mm long sections of 150 mm diameter pipes having 6 mm wall thickness. The impact energy required to just initiate the damage in glass fiber reinforced/epoxy pipes was found to be larger than the energy needed for glass fiber reinforced/vinylester pipe. The load-time curves also reveal that vinyl ester-based pipes exhibit a ductile failure under impact, whereas, in the epoxy-based pipes the failure was rather brittle in nature.

Study of Acoustic Emission in a Compression Test of Andesite Rock

In the compression test of a material's sample, elastic waves produced by dynamic processes are known as acoustic emissions (AE). These waves, which propagate from the source to the material surface, arrive to the piezoelectric sensor where they are converted to electric signs and transformed into the typical AE parameters. These parameters will be employed for the evaluation of failure mechanisms present in the test. In this work, the mechanic behaviour of andesite's rocks of Cerro Blanco, San Juan, Argentina was studied. Two compression tests were performed for two cylindrical rock samples and the AE parameters were measured. The measurement configuration consisted of two syntonized sensors at 60kHz and 150kHz placed on the lateral face of the sample. The AE parameters registered were amplitude, duration, energy, RMS, etc. This data group was related to the load–time curve. Different indicators like average frequency and the ratio of rise–time to amplitude of the signal were calculated. These indicators were analyzed and evaluated with the purpose of identifying the damage level and the type of failure.

Experimental Study on Load-Settlement Behaviour of Cement Stabilised Footing with Different Dimensions on Sandy Soil

Laboratory tests were done to study the load-settlement behaviour. These tests evaluated rigid square footing on sandy soil and a layered system, stabilised with different dimensions and different cement contents. Nineteen plate load tests were done to make evaluations. The soil type used in tests was poorly graded sand in a box container with the following dimensions; cross section 130 cm × 130 cm and depth 100 cm. The soil was compacted in layers 10-cm thick. Cement was added in percentages of 2.5, 5 and 7.5 % by dry weight of soil. Samples were cured for 28 days, after which they were tested. Experimental data demonstrated effectiveness in terms of increasing bearing capacity and reducing settlement of the stabilised soil–cement layers. Results also showed difference in terms of crack propagation mechanism between samples with different cement contents as evaluations of number and direction. The load-time curves determined from test data showed that the required time to make constant the load variation versus time was more in those samples with 7.5 % cement content compared to those with cement contents of 2.5 and 5 %.

Low-velocity impact behavior of hollow core woven sandwich composite: Experimental and numerical study

Low-velocity impact analysis of 3D woven hollow core sandwich composite was conducted experimentally and numerically. Damage modes, perforation loads, load-time and energy-time curves, contact time, force-displacement and deflection-energy relationships were studied for three energy levels on specimens with different thicknesses utilizing both FE simulations and low-velocity impact tests. According to the results, contact stiffness and perforation load decreased with the panel thickness, whereas panels of higher thicknesses exhibited higher energy absorption capacity. The FE model consisting of glass fabric and surrounding resin reasonably predicted the impact behavior and damage modes. Subsequently, it could be inferred that FE simulation is capable to be used instead of time-consuming experiments to study impact properties of such materials.

Study on the kinetics of thermomechanical response accompanying plastic instability in mild steel

This paper deals with the analysis of heat power and strain rate evolutions accompanying Lüders instability in mild steel to quantitatively probe the kinematics of the associated localization during tensile testing. Thermomechanical parameters such as dissipative heat power, stored power and energy conversion rate ratios are estimated to provide an insight into the deformation behavior and the associated rate of energy conversions involved in each region of the load–time curve. It is shown that compared to temperature and strain evolutions, heat power and strain rate evolutions provide more quantitative information on the plastic strain localization during nucleation and growth of Lüders bands without the effects of the signatures of prior plastic localization. The occurrence of delayed localized yielding during the initial stages of uniform strain hardening is successively studied using heat power and strain rate evolutions. The difference in magnitude of yielding experienced by the specimen during the propagation of two different Lüders bands is clearly demonstrated by the estimated dissipative heat and stored powers. Estimated energy conversion rate ratios convey that fraction of heat power dissipated is relatively more in the load plateau involving strain localizations than the strain hardening region.

Preparation of hydroxypropyl cellulose microfibers by high-speed rotary spinning and prediction of the fiber-forming properties of hydroxypropyl cellulose gels by texture analysis

Water-soluble, nonionic cellulose-based fibers were prepared from aqueous hydroxypropyl cellulose gels of 5–13-μm diameter by using a high-speed rotary spinning technique. A combination of texture analysis and viscosity measurement was applied to determine the optimum concentration of hydroxypropyl cellulose gels for fiber formation. The examined concentration range of hydroxypropyl cellulose gels was 38–52 % w/w. The textural properties including the adhesiveness of gels of different concentrations were determined based on the load-distance and load-time curves, while the obtained fiber formation was visually observed with an optical microscope. The texture analysis method enabled the determination of the optimum gel concentration from the point of fiber formation. An unequivocal correlation was determined between the adhesiveness of gels and their fiber-forming ability. The adhesiveness has a local minimum where the productivity of the fiber formation process and the micromorphology of the emitted fibers are optimal. Statistical analysis of the distribution of fiber diameters confirmed that in case of the optimum concentration, the distribution approaches normality. Mechanical properties of the prepared fibers were also evaluated using texture analysis, which indicated that the fibers made of gels of the suggested optimum concentration had the most desirable elastic behavior. An optimum concentration range of hydroxypropyl cellulose exists that enables fiber formation with the required characteristics from the point of further pharmaceutical formulation processing.

Quantitative analysis of the material flow in transitional region during isothermal local loading forming of Ti-alloy rib-web component

The material flow in transitional region plays an important role in the forming quality of transitional region in the isothermal local loading forming of titanium alloy large-scale rib-web component. To study the material flow in transitional region, the finite element (FE) model of transitional region was established based on DEFORM-2D software and validated by physical experiment. Then, a quick and easy method, which can measure the area of different local regions of forged part in DEFORM-2D via user subroutine, was proposed to achieve the quantitative analysis of material flow mechanism. This technique can also be used in the analysis of other forming process, such as the calculation of fill ratio in forging process. The material flow pattern of transitional region during local loading forming was analyzed step by step and compared with integral forming. The results show that the material flow of transitional region during local loading process can be divided into six stages according to the material flow pattern and load-time curve. Twice transverse material flow with opposite directions occurred in the first and second loading steps sequentially, which does not exist in the integral forming. Four characteristic values evaluating the transverse flow of material, which are associated with the formation of defects and their severities, are defined and quantitatively measured at various processing conditions. It is found that decreasing the spacer block thickness and increasing friction both can decrease the four characteristic values, thus weaken the transverse material flow, which are helpful to improve the forming quality in transitional region. However, the transverse flow of material is little affected by the loading speed.

On the effect of gating system type on occurrence of hot tears in Al–4 wt% Cu castings

In this study, effects of gating system type on hot tearing occurrence of Al–4 wt% Cu castings were investigated using the instrumented constrained T-shaped casting method. Three different gating systems, i.e. a conventional pressurized gating system, a conventional unpressurized gating system and a naturally pressurized gating system with surge control arrangement, were used for this purpose. The presence of oxide bifilms in torn surfaces were studied using scanning electron microscopy and energy-dispersive x-ray spectroscopy. It was shown that hot tearing severity could be predicted from the final slope of the load–time curves. Hot tearing susceptibility was highest for the conventional pressurized gating system. This was associated with the high surface turbulence of the melt during mould filling which would result in the formation of such defects as oxide bifilms. For the naturally pressurized gating system, the maximum load tolerable by the solidifying casting was much larger than those for conventional gating systems and severity of hot tears formed were much less significant. Hot tearing occurrence in all the castings was closely associated with the presence of thick oxide layers. In other words, greater amounts of oxide bifilms were observed on the hot tearing surfaces of the more severely torn castings.

Low velocity impact behaviour of glass fabric/epoxy honeycomb core sandwich composites

Abstract In this paper, the low velocity impact characteristics of honeycomb sandwich panels with varying cell sizes such as the maximum load absorbed, absorbed energy and failure modes were investigated. Low-velocity impact tests were carried out at different energy levels using an instrumented drop-weight apparatus as per ASTM D3029-95. Honeycomb core sandwich composite panels were made with glass fabric/epoxy honeycomb core with different cell sizes i.e., 8, 12, 16 and 20 mm using the vacuum bag molding technique. Tests were conducted at impact energies that ranged ranging from 7 to 50 J. The energy absorption mechanism and the damage process are analysed with parameters derived from the load-time and energy-time curves. It is observed that at low energy levels, the core buckles while it gets crushed at higher levels. This buckling of the core is due to damage to the epoxy resin that allows the glass fiber to bend freely, and core crushing is due to the breakage of the glass fiber reinforcement within the core. It is inferred that for a given core height, as the cell size increases, the peak load at which cracking occurs in the face sheet decreases drastically. This is attributed to the fact that a core with a smaller cell size has fewer load paths to distribute the absorbed energy. It is evident from the post impact damage analysis that three types of failure modes occur viz., crack initiation, cracking of the face sheet along with debonding, and the crushing of cells. The common damage pattern observed on the front facing has a square shape which is the same as the shape of the indentor.

Investigation on Finite Element Simulation of ECAE with Variable Back Pressure for 7075 Aluminum Alloy

The numerical simulation of equal channel angular extrusion (ECAE) with variable back pressure was researched by applying the commercial Deform-3D software, in which choosing the hard deformation materials of 7075 aluminum alloy, and comparing the traditional ECAE without back pressure process. The influence of back pressure on the mean stress and the effective strain rate in the shear deformation zone was studied. The results show that the extrusion force transformation laws were different in both load ways, with the increase of back pressure, extrusion force enhances increasingly, but the final load-time curves tended towards stability, but in ECAE without back pressure, the final load-time curves tended towards decreasing; thus the whole deformation process can be divided into different stages. In addition, the larger the absolute value of the hydrostatic stress at the corner, the more beneficial to refine grain and improve the plasticity. The back pressure makes the distribution of effective strain rate in plastic deformation area more uniform and improves the uniformity of deformation.

OS1742 人工水晶の破壊挙動と発光現象

When In this study, uniaxial compression tests for synthetic quartz were carried out at quasi-static and dynamic rates to clarify the relationship between the luminous phenomena and the stress-strain curves. The intensity of light generated in the fracture of quartz was measured by a photodiode with photo-sensor amplifier. The fracture manners of quartz such as the number of fragments, the area of fracture surface and the volume of fragments were also examined. Even in the static test, dynamic response of load associated with fracture was precisely evaluated by the load cell apart from the specimen with taking account of unloading stress wave propagation. It was clearly found that the peaks in the signal record of light generated during the fracture of quartz correspond to the changing points of the slope on load-time curves. Especially, the largest peak was measured at the dramatic drop of the load due to the fracture of quartz. The total quantity of light from fracture surface generated in dynamic compression tests was greater than that observed in static tests because the finer fracture fragments collected after dynamic tests provides the wider area of the fracture surface than those in static tests.

An Acoustic Emission Study for Monitoring Anterior Cruciate Ligament Failure Under Tension

The analysis of the acoustic signals produced during anterior cruciate ligament (ACL) failure could be useful in understanding its behavior. The purpose of the present study was to evaluate the role of coupling conditions of the sensors and to determine the value of newly introduced acoustic emission (AE) parameters. Seven femur-ACL-tibia complex (FATC) specimens were fixed in a universal tensile testing machine and load was applied. Different coupling conditions were applied in two groups of specimens. The load-time curve was monitored, with the simultaneous recording of the acoustic signals and the failure mode. During ACL tear, detectable changes in the load-time curve occurred linked to changes in the macroscopic sequence of events and the measured AE parameters irrespective the coupling conditions. AE provides information on the determination of the moment (or load) when crucial irreversible damage occurs. Furthermore, specific AE indices exhibit changes throughout the testing, and imply shift of the failure mechanisms.

Regeneration of Periodontal Ligament for Apatite-coated Tooth-shaped Titanium Implants with and without Occlusion Using Rat Molar Model

Regeneration of periodontal ligament (PDL) is still a major issue in implant dentistry. In this study, we evaluated the effects of hydroxyapatite (HA) coating and occlusion on the regeneration of PDL around tooth-shaped titanium implants with root form. Three groups of tooth-shaped titanium implants, namely, non-HA-coated without occlusion (HA-/OCL-), HA-coated without occlusion (HA+/OCL-), and HA-coated with occlusion (HA+/OCL+), were immediately implanted into extracted tooth sockets with remaining PDL of rat molar model and the regeneration of PDL was examined histomorphometrically and histologically. Direct bony attachments were formed at the HA+/OCL- implant interface. In contrast, soft peri-implant tissue was distinctly seen between the HA+/OCL+ implant surface and surrounding alveolar bones. The shape of the load-time curve for the HA+/OCL+ group was similar to that for natural teeth. Peri-implant tissue of the HA+/OCL+ implants exhibited alkaline phosphatase with a distribution and activity similar to those of the PDL. Collagen fiber bundles were found functionally oriented in some regions of the peri-implant tissue. These findings indicate that the remaining PDL tissue around extracted sockets has the ability to regenerate bone and PDL-like tissues on HA-coated tooth-shaped implants. Occlusal loads to the HA-coated implants may induce regeneration of PDL-like tissue in the peri-implant tissue.

Dynamics Simulation for Horizontal-Axis Wind Turbines

In this study, the dynamic characteristics of three-blade horizontal¬-axis wind turbines were simulated, based on the aerodynamic software AeroDyn, wind turbine design software FAST and mechanical dynamics simulation software ADAMS. AeroDyn and FAST are Interface codes for ADAMS. As the pre-processor of ADAMS, FAST code helps to build wind turbine model as well as constrains ,while AeroDyn code applies wind field data to the model. At last the model was imported into ADAMS to be simulated. In this way, the dynamic operating characteristics of three-blade horizontal¬-axis wind turbines can be obtained. And the load-time curves of the blade roots can also be gotten. Results show that the method adopted is feasible and reliable.

Studies on the Low-Velocity Impact Response of Ultra-High Molecular Weight Polyethylene Laminated Composites

The low-velocity impact response of Ultra-High Molecular Weight Polyethylene (UHMWPE) laminated composites were studied by drop-weight experiments. Laminated composites were fabricated with unidirectional UHMWPE prepreg using hot-pressing process. Laminated composites of size 150mm×100mm were subjected to low-velocity impact loading at three energy levels of 15J, 25J and 35J. It is found that the slops of load-time and energy-time curves increase with increase in the impact energy. However, load-time curve shows that there are some fluctuations before the peak load was reached. Peak load and absorbed energy increase with increasing impact energy. However, time to peak load decreases linearly with increasing impact energy.

The Simulation of Compression Performance of Aluminum Foams Base on DEFORM

Two kinds of cell models, include of Octahedron cell model and Tetrakaidecahedron cell model, were analyzed for the open-cell Aluminium foams. Simulation results show that the compression load-time curves of the two models have the same trend. There are three stages, elastic region, yield region, densification region. In addition, The Tetrakaidecahedron model calculation and predication show good agreement with the experimental results. Its simulation results of platform stress closer to the experimental value in the two models. Therefore, Tetrakaidecahedron model was the best choice to simulate the aluminium foams.

Numerical and experimental study on the interaction cable structure during the failure of a stay in a cable stayed bridge

Corrosion, abrasion and fretting fatigue may cause deterioration and, eventually, the failure of a post-tensioning tendon or a stay cable on a cable supported structure. In the present study, the stress acting during the rupture on the remaining portion of the stay which fails is derived, and the role of the rupture time on the response of the structure is discussed from a theoretical and a numerical point of view. In addition, the load–time curve during the rupture and the total time of the rupture of undamaged and damaged wires of seven-wire steel strands are investigated in an experimental program defined on the basis of the previous theoretical results. In the locally damaged specimens, a notch is machined into their outer wires. The specimens are tested under tension at three different strain rates in order to determine the influence of this parameter on the rupture time and on the load–time curve. The damaged specimens also allow us to determine the influence of a local reduction of the cross section on the stiffness and ultimate load of the specimen.

The Compression Behavior Simulation of Aluminum Foams

The compression behavior of open-cellular Aluminum foams was simulated using DEFORM-3D software. The structures of regular tetrahedron, octahedron and tetrakaidecahedron (Kelvin) model were developed separately. Simulation results show that the models have similar compression behavior. Then load-time curves and strain-stress curves have similar characteristics, the linear elasticity at low stresses followed by a long collapse plateau, truncated by a region of densification in which the stress rises steeply. Compared with experiment, the platform stress and the Young’ model of the Kelvin mold have good consistency within the error range.

Numerical Simulation and Deformation Research for Cold Enlarging Tube Diameter

This paper presented how to build finite element model based on UG NX, and simulated the cold expanding process by DEFORM software. The deformation, distribution and development trend of velocity, equivalent stress, equivalent strain and equivalent strain rate were predicted. The punch’s load-time variation curves in X, Y and Z direction were also obtained.

Surface Effect Preparatory Research of Vibrational Rotary Forging

As lack of a efficiency theoretical approximate solution for the surface effect mechanism analyzed during continuing and local vibrational plastic deformation process, according to vibrational rotary forging deforming characters, a three-dimension visco-elasticity plasticity constitutive equation was built by Kelvin model and Liewei-Mises model. After this constitutive equation was to be matrixing and to be introduced to tetrahedral solid elements, a visco-elasticity spatial stiffness matrix and a visco-plasticity spatial stiffness matrix were respectively derived. According to experimental parameters given, some simulation experimental projects were designed, a FEM models were established, and some FEM experiments were done on condition that amplitude and vibrational frequency were respectively changed, then different normal load-time curves were obtained. It is shown from experiment results that surface effect will appear during vibrational rotary forging forming process with little amplitude, the surface effect is related to the amplitude and the frequency, and this effect generation should be in special conditions, then preparatory research of surface effect mechanism of continuing and local vibrational plastic deforming process.