Varying Drop Heights Research Articles

A study on cob sample production and techniques

This paper deals with the validation of a cob sample production technique that replicates the on-site wall construction method. Cob cubes were prepared under confined and unconfined conditions with varying drop heights (0.50, 0.75 and 1.00 m) and moulding water contents (25.7–39.7%) by mass of soil. Prior to mass production of samples, a trial test was performed at a constant drop height of 0.75 m and varying water contents. Based on the trial test results, the other two drop heights of 0.50 and 1.00 m were adopted for further validation. The effects of confinement, drop height and moulding water content on the compressive strength and density of cubes were studied. Test results show maximum compressive strengths and densities ranging from 1.22 to 1.31 MPa and 1.65 to 1.70 g/cm3, respectively, at a 33.7% water content and a 0.75 m drop height, with those for the confined specimen being the highest. The strength and density values obtained satisfy the guidelines prescribed by some standards. Thus, the proposed technique for cob production may be adopted to achieve desirable compressive strength and density for the particular soil used in the present study.

Energy dissipation due to breakage during confined compaction of granular materials

The dissipation of energy during the compaction of granular materials was studied by performing confined drop tower experiments on Ottawa sand. Energy dissipated due to breakage was quantified by evaluating the creation of new surfaces at varying drop heights. Post-compaction particle size distributions (PSD) were measured and the amount of breakage was quantified by the position of the current PSD relative to the pre-compaction and ultimate PSD. Our observations revealed that the percentage of input energy dissipated due to breakage accounted for less than 0.5% of the total energy budget and was a constant proportion regardless of the total energy applied to the system. We also evaluated the effects of die wall friction by measuring post-compaction PSD in various positions within the sample.

High-density electromyographic assessment of stretch reflex activity during drop jumps from varying drop heights

This study investigated how drop heights and their associated drop jump performance relate to stretch reflex modulations. Eleven male subjects performed ten drop jumps from each of three individually predetermined drop heights. These were the drop height resulting in maximal performance (OPT), as well as 10 cm below (LOW) and above (HIGH) maximal performance. To quantify drop jump performance the reactive strength index, derived from force plate measures, was used. High-density surface EMG provided both stretch reflex response timing and size, as well as novel insight into the associated motor unit recruitment via muscle fiber conduction velocity estimations. These measures were examined in the vastus lateralis (VL), soleus (SOL) and gastrocnemius medialis (GM).Drop jump performance improved by 9% (p < 0.001) from LOW to OPT and decreased by 5% (p = 0.008) from OPT to HIGH. Despite decreasing performance, stretch reflex responses were largest at HIGH. Stretch reflex responses timing did not change; staying within the short (SOL, <60 ms) and medium (VL, GM; 60–85 ms) latency response time-frames. Motor unit recruitment appeared to change across drop heights only for VL, whereas activation intensity only changed for SOL. These results indicate that during drop jumps above OPT neuromuscular modifications result in VL no longer being maximally recruited.

Ankle dorsiflexion range of motion is associated with kinematic but not kinetic variables related to bilateral drop-landing performance at various drop heights

Limited evidence is available concerning ankle dorsiflexion range of motion (DF ROM) and its relationship with landing performance from varying drop heights. The aim of this investigation was to determine the relationship between ankle DF ROM and both kinetic and kinematic variables measured during bilateral drop-landings from 50%, 100% and 150% of countermovement jump height. Thirty-nine participants were measured for their ankle DF ROM using the weight-bearing lunge test, after which five bilateral drop-landings were performed from 50%, 100% and 150% of maximal countermovement jump height. Normalized peak vertical ground reaction force (vGRF), time to peak vGRF and loading rate was calculated for analysis, alongside sagittal-plane initial contact angles, peak angles and joint displacement for the hip, knee and ankle. Frontal-plane projection angles were also calculated. Ankle DF ROM was not related to normalized peak vGRF, time to peak vGRF or loading rate (P > 0.05), regardless of the drop height. However, at drop heights of 100% and 150% of countermovement jump height, there were numerous significant (P < 0.05) moderate to large correlations between ankle DF ROM and initial contact angles (r = −0.34 to −0.40) and peak angles (r = −0.42 to −0.52) for the knee and ankle joint. Knee joint displacement (r = 0.39–0.47) and frontal-plane projection angle (r = 0.37–0.40) had a positive relationship with ankle DF ROM, which was consistent across all drop heights. Ankle DF ROM influences coordination strategies that allow for the management of vGRF during bilateral drop-landings, with alterations in alignment for the knee and ankle joints at both initial contact and peak angles.

Heavy-weight impact testing: Test repeatability for a modified kettlebell and comparison of impact source weights and drop heights

Noise and vibration from heavy-weight impacts associated with fitness activities are a common source of complaints in hotels, multi-family residences, and corporate office spaces. In situ testing using various heavy/hard impact sources is commonly used to evaluate the effectiveness of mitigation measures to address noise and vibration complaints. Previous work (LoVerde et al., Internoise 2015) proposed the use of a 16-lb spherical shot for in situ testing. However, significantly heavier weights are common in many gyms. For instance, hotel chains commonly include free-weights with a range of 5 to 75 lb in their fitness rooms. It is not known if the relatively light 16-lb shot provides results that are indicative of impacts from significantly heavier weights. This presentation evaluates the use of heavier (50-lb and 100-lb) kettlebells and varying drop heights as alternates to the 16-lb shot. Additionally, this presentation evaluates test repeatability for the kettlebells which have been modified so that the impact surface is spherical in shape.

Determination of apple bruise resistance based on the surface pressure and contact area measurements under impact loads

The bruises as well as other affects in fruit quality cause lower selling prices and generate loss for fruit growers. For proper identification of damages in biological material, the impact load, contact pressure as well as force affecting on apple skin should be examined. In this paper, the authors present an experimental method in assessing of the bruise resistance as well as the bruise threshold for the 'Gala' apple cultivar consisting a relationship between the impact loads during free drop against four rigid surfaces. The authors measured the contact surface between tested fruit and fixed material to determine the bruise resistance. The Tekscan® measuring system was applied to determine the contact surface and the surface pressures at the moment of collision during impact test. Damaged tissue was photographed and subjected to the computer image analysis in order to determine the bruise volume. In this study, the bruise resistance index (BRI) as relationship between determined bruise volume and surface pressure at varying drop heights was presented. Due to the difficulty and time–consuming process of the bruise volume evaluation, the authors decided to replace commonly used method with functional relation of the contact surface. It allowed for assessing the alternative BRIc indicator which was based on the relationship between the surface pressure and the contact surface. Both the indicators as well as verifying linear regression analysis showed, that proposed BRIc power model with high precision describes power curves of the BRI indicator. From conducted analysis results that the BRIc indicator allows for the determination of the bruise resistance for the 'Gala' apple cultivar and precisely describes the BRI indicator. Based on the BRIc curves and changes in the bruise area–drop height relationship, a graphical method in assessment of the bruise resistance and the bruise threshold was proposed. The presented method can be used as effective tool in mechanical damage assessing.

Area-Array of 3-Arc-Fan Compliant Interconnects as Effective Drop-Impact Isolator for Microsystems

Compliant off-chip interconnects as the first-level and second-level compliant interconnect structures are able to accommodate the differential displacement between the die and the substrate or between the substrate and the board due to their high in-plane and out-of-plane compliance. This paper presents experimental and simulation results of drop testing of silicon substrates with micro-scale copper compliant interconnects assembled on organic boards. The micro-scale copper compliant interconnects in this paper are three-arc-fan compliant interconnects with arcuate beam width equal to 10, 15, and 20 $\mu \text{m}$ , respectively. The samples with three-arc-fan compliant interconnects were subjected to drop tests at varying drop heights ranging from 20 to 50 cm in steps of 10 cm. The experimental and simulation results were compared against the corresponding results obtained from the samples assembled with the solder ball interconnects. Through drop-test experiments and simulations, it is shown that the three-arc-fan compliant interconnects when scaled down in size and fabricated through copper electroplating process are able to isolate the strain transferred from an organic board to a silicon substrate, and that the impact isolation increases with the increased compliance of the interconnects. [2015-0205]

Evaluation of bruise resistance of pears to impact load

The main cause of bruises resulting in loss for fruit growers are dynamic and impact type loads to which fruit is exposed during harvesting, loading and transport. Due to the characteristic shape of the contact plane of the fruit during the impact with the hard surface of e.g., a box or another fruit, there appears a problem of pressure force concentrated in a small area, leading to local exceeding of allowable limits. The authors focused on experimental procedure aimed at quantitative assessment of damage to the ‘Clapp’s Favorite’ pear fruit depending on the changes in surface pressures that occur during impact loads. The study analyzed the influence of impact loads on the bruise resistance by measuring the surface pressures at varying drop heights and a specified number of impacts. The Tekscan® system was applied to determine force impulse values and contact plane areas, which enabled the calculation of surface pressure distribution. A computer analysis of the images of damaged tissue was carried out in order to determine the bruise volume, and a method for evaluating bruise resistance in pears was proposed based on the obtained BRI indicators (bruise resistance index—relationship between contact pressure and bruise volume). Both the analysis of the instantaneous force values, contact planes and surface pressures, as well as verifying analysis of the volume images enabled to determine bruise resistance in the case of the investigated ‘Clapp’s Favorite’ pears at level of 8%. Also the pear bruise threshold was estimated at 46mm with force impulses of up to 100N. The presented method allows for the determination of the bruise resistance of fruits with high water content by measuring the surface pressure, accounting for the shape of the fruit’s surface, mechanical properties of the flesh, and compression force.

Impact Isolation Through the Use of Compliant Interconnects for Microelectronic Packages

First-level and second-level compliant interconnect structures are being pursued in universities and industries to accommodate the differential displacement induced by the coefficient of thermal expansion mismatch between the die and the substrate or between the substrate and the board. The compliant interconnects mechanically decouple the die from the substrate or the substrate from the board, and thus reduce the thermally induced stresses in the assembly. This paper presents drop-test experimental and simulation data for scaled-up prototype of compliant interconnects. The simulations were based on Input-G method and performed using ANSYS® finite element software for varying drop heights. In parallel to the simulations, scaled-up compliant polymer interconnects sandwiched between a polymer die and a polymer substrate were fabricated using three-dimensional (3D) printing, and this fabrication provides a quick low-cost alternative to cleanroom fabrication. The prototype of the assembly was subjected to drop tests from varying drop heights. The response of the assembly during drop testing was captured using strain gauges and an accelerometer mounted on the prototype. The data from the experiments were compared with the predictions from the simulations. Based on such simulations, significant insight into the behavior of compliant interconnects under impact loading was obtained, which could be used for reliable design of compliant interconnect under impact loading. Both the experimental and simulation data reveal that the compliant interconnects are able to reduce the strains that transfer from substrate to die by one-order.

Determining the impact behavior of concrete beams through experimental testing and meso-scale simulation: II. Particle element simulation and comparison

A complete model of the hammer–transducer–concrete beam system using meso-scale particle elements is proposed. Drop-weight tests are performed with a constant weight and varying drop heights. The numerical results are compared with those from the impact tests in Part I. The results of impact loads, deflections, and strains exhibit satisfactory agreement. The validated model is then used to predict dynamic behavior under higher loading rates. Different fracture modes are observed in the simulation. The strain-fracture energy concept is introduced to particle element modeling and the energy conversion between kinetic and strain-fracture energy components are discussed for different strain rates.

Measuring and Modeling of Oxygen Transfer Rate in a Drop Structure

Oxygen mass transfer in drop structures plays important roles in natural waters such as cascade waterfalls and in wastewater treatment facilities such as sewer collection systems and equalization tanks. To assess the oxygen transfer rate in drop structures, the oxygen mass transfer process was studied in a tank with water recirculation and impingement. A series of un-steady-state reaeration experiments with varying water recirculation rates (4−12 L/min), varying drop heights (0.6−1.4 m), varying water depths (0.6−1.4 m), and varying water temperatures (18.7−29.5 °C) were performed, and the reaeration data were analyzed by a mass transfer model considering the oxygen transfer processes in the droplet and surface mass transfer zones. The experimental results showed that the oxygen transfer rate of the surface mass transfer zone increased with increasing water recirculation rate, or drop height, while the oxygen transfer rate of the droplet mass transfer zone increased with increasing water recirculation rat...

Effect of damage on flexural modulus of C/C–SiC composites

The aim of the present work is to study the influence of damage in carbon–carbon silicon carbide composites (C/C–SiC) on their flexural resonant frequency as well as their flexural elastic modulus. Composite samples were examined by the grindosonic method and confocal laser scanning microscope before and after impact damage. Damage was introduced by the drop-weight (low-velocity) impact method using varying drop heights. The results show that the changes of the flexural resonant frequency after delamination/cracking of the matrix, compared to those of non-delaminated specimens, gave a good indication of the degree of damage, confirmed that the microcrack reduces the flexural resonant frequency and gave lower values of the modulus of elasticity.

Redesigning protective packaging buffers from the failure modes derived from crack characteristics

Protective packaging buffers are commonly used for the purpose of containment, protection, communication, and marketing of consumer products. Because the use of protective packaging is expected to increase markedly in the years ahead, it is imperative that their designs be cost-effective. Much of the known design heuristics have been encapsulated in design methodologies and procedures, except for one aspect, that is, the failure modes of the buffers upon impact with the ground after being dropped from a height. All packaging designs are subjected to a series of confirmatory impact tests, before design deficiencies are rectified through iterative cycles of redesign and retest. Because of the heuristic nature of packaging design, many cycles of redesign are necessary before a satisfactory design solution is found. This article discusses how, from the nature and severity of the cracks, the probable causes of failure and corrective redesign measures may be estimated. Based on the value of the crack ratio (i.e., the ratio of the depth of the crack to the buffer's bearing thickness), three distinct modes of failure can be identified: marginal, critical, and catastrophic. The variation of G-value with crack ratios was studied for varying drop heights. By comparing the measured G-value to the failure mode, the conditions contributing to the failure—viz. height of drop, direction of impact, the location of the centroid, the type of fit, and degree of contact between the buffer and the product—may be estimated. Redesign guidelines to avert catastrophic buffer failure are also discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 721–731, 1999

Redesigning protective packaging buffers from the failure modes derived from crack characteristics

Protective packaging buffers are commonly used for the purpose of containment, protection, communication, and marketing of consumer products. Because the use of protective packaging is expected to increase markedly in the years ahead, it is imperative that their designs be cost-effective. Much of the known design heuristics have been encapsulated in design methodologies and procedures, except for one aspect, that is, the failure modes of the buffers upon impact with the ground after being dropped from a height. All packaging designs are subjected to a series of confirmatory impact tests, before design deficiencies are rectified through iterative cycles of redesign and retest. Because of the heuristic nature of packaging design, many cycles of redesign are necessary before a satisfactory design solution is found. This article discusses how, from the nature and severity of the cracks, the probable causes of failure and corrective redesign measures may be estimated. Based on the value of the crack ratio (i.e., the ratio of the depth of the crack to the buffer's bearing thickness), three distinct modes of failure can be identified: marginal, critical, and catastrophic. The variation of G-value with crack ratios was studied for varying drop heights. By comparing the measured G-value to the failure mode, the conditions contributing to the failure-viz. height of drop, direction of impact, the location of the centroid, the type of fit, and degree of contact between the buffer and the product-may be estimated. Redesign guidelines to avert catastrophic buffer failure are also discussed.