Drop Impact Test Research Articles

Improvement of sound absorption coefficient of glass fiber fabric epoxy composite inherently without deterioration of main mechanical properties

In this study, the sound absorption behaviour of glass fiber fabric epoxy composite (GFFEC) is aimed to be increased without reduction in main mechanical properties and density. The effect of polystyrene (PS) and silica aerogel (SA) on sound absorption, density, tensile, and flexural properties along with drop impact performance of GFFEC were investigated. Both PS and SA was added into epoxy resin. Vacuum infusion method was applied to manufacture GFFEC’s. Both PS and SA addition resulted with enhanced sound absorption coefficient (SAC) of GFFEC. Breaking stress and elongation enhanced with either PS or SA addition. Increased absorbed energies during drop impact tests were observed in both PS and SA incorporated GFFEC’s compared to reference GFFEC. Density of reference composite (lightness) has improved by addition of SA and PS. Additionally, use of SA improved the SAC of GFFEC. On the other hand, maximum SAC was achieved with use of PS rather than SA.

Structural health monitoring of fiber reinforced composites using integrated fiber optics network

This study investigates the detection of internal crack in a material using reinforced optic fiber bundle. There are many external crack detection techniques available but when we look upon internal crack there are only few techniques available which is complex and expensive. So, to overcome this problem we adopted this internal crack detection technique which is compact and cheap using the grid system. The scope of our study is to solve the general problem which occurs during manufacturing of a product which exposes the final material under stress. Four samples were made which had Glass Fiber Mat and the Optic Fiber induced into the samples in X and Y axis. Then the sample was subjected to Drop Impact Test and Flexural Test through which the damage was induced. The light was passed through the optic fiber bundle in uniform way at the entrance. The intensity of light was measured using the lux meter and the change in intensity of light before and after testing was depicted in the graph. It was found that the variation in the optic fiber damage where the crack was induced were able to be detected at the exit fibers arranged in the linear way. Thus the grid points were noted down and the point of damage was able to be narrowed down using this technique The exact effect of this study can be employed in the construction site which are located in the earthquake prone zones so that we can identify the internal cracks in the building and protect them before major accident occurs in the future.

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Structural Monitoring of Glass Fiber/Epoxy Laminates by Means of Carbon Nanotubes and Carbon Black Self-Monitoring Plies.

The health monitoring of structures is of great interest in order to check components’ structural life and monitor damages during operation. Self-monitoring materials can provide both the structural and monitoring functionality in one component and exploit their piezoresistive behavior, namely, the variation of electrical resistivity with an applied mechanical strain. In this work, self-monitoring plies were developed to be inserted into glass-fiber reinforced epoxy-based laminates in order to achieve structural monitoring. Nanocomposite epoxy-based resins were developed employing different contents of high surface area carbon black (CB, 6 wt%) and multiwall carbon nanotubes (MWCNT, 0.75 and 1 wt%), and rheologically and thermomechanically characterized. Self-monitoring plies were manufactured by impregnating glass woven fabrics with the resins, and were laminated with non-sensing plies via a vacuum-bag process to produce sensored laminates. The self-monitoring performance of the laminates was assessed during monotonic and cyclic three-point bending tests, as well as ball drop impact tests. A higher sensitivity was found for the CB-based systems (Gauge Factor 6.1), while MWCNTs (0.55 and 1.04) ensure electrical percolation at lower filler contents, as expected. The systems also showed the capability of being used to predict residual life and damage occurred under impact.

An Approach to Characterize the Impact Absorption Performance of Construction Helmets in Top Impact

The helmets used by construction site workers are mainly designed for head protection when objects are dropped from heights. Construction helmets are also casually called "hard hats" in industries. Common construction helmets are mostly categorized as type 1 according to different standards. All type 1 helmets have to pass type 1 standard impact tests, which are top impact tests-the helmet is fixed and is impacted by a free falling impactor on the top crown of the helmet shell. The purpose of this study was to develop an approach that can determine the performance characterization of a helmet. A total of 31 drop impact tests using a representative type 1 helmet model were performed at drop heights from 0.30 to 2.23 m, which were estimated to result in impact speeds from 2.4 to 6.6 m/s. Based on our results, we identified a critical drop height that was used to evaluate the performance of helmets. The peak impact forces and peak accelerations varied nonproportionally with the drop height. When the drop height is less than the critical height, the peak force and peak acceleration increase gradually and slowly with increasing drop height. When the drop height is greater than the critical height, the peak force and peak acceleration increase steeply with even a slight increase in drop height. Based on the critical drop height, we proposed an approach to determine the safety margin of a helmet. The proposed approach would make it possible to determine the performance characteristics of a helmet and to estimate the safety margin afforded by the helmet, if the helmet first passes the existing standardized tests. The proposed test approach would provide supplementary information for consumers to make knowledgeable decisions when selecting construction helmets.

Performance of identical rockbolts tested on four dynamic testing rigs employing the direct impact method

Impact drop tests are routinely used to examine the dynamic performance of rockbolts. Numerous impact tests have been carried out in the past decades on independently designed, constructed and operated testing rigs. Each laboratory has developed testing procedures; thus, the results are often reported in different ways by various laboratories. The inconsistency in testing procedures and reporting formats presents a challenge when comparing results from different laboratories. A series of impact tests of identical rockbolts was carried out using the direct impact method (i.e. the mass free-fall method) on the rigs in four laboratories in different countries. The purpose of these tests was to investigate the level of consistency in the results from the four rigs. Each rig demonstrated a high level of repeatability, but differences existed between the various rigs. The differences would suggest that there is noticeable equipment-dependent bias when test results obtained from different laboratories are compared. It was also observed that the energy dissipated for the plastic displacement of the bolt was smaller than the impact energy in the tests. The average impact load ( AIL ) and the ultimate plastic displacement ( D ) of the bolt describe the ultimate dynamic performance of the bolt. In the case where the bolt does not rupture, the specific plastic energy ( SPE ) is an appropriate parameter in describing the impact performance of the bolt. Two other relevant parameters are the first peak load ( FPL ) and the initial stiffness ( K ) of the bolt sample. The information from this test series will guide the formulation of standardised testing procedures for dynamic impact tests of rockbolts.

Mechanical properties and X-ray diffraction analyses of clay/sand pellets for CO2 adsorption: the effects of sand content and humidity

In this work, we report the mechanical properties of an alternative material based on a mixture of natural clay and ferruginous sand in pellet form for CO2 capture. These raw materials were collected from Ecuador, and they contain iron and titanium oxides from volcanic origin. To evaluate the effect of the sand content on the mechanical properties of pellets, the samples were manually prepared with 0 (control sample), 15, and 25 wt.% sand contents and analyzed using free-fall drop impact and uniaxial compression tests. The uniaxial compression test was carried out under three conditions: using sieved sand, using sand without sieving, and under wet conditions. The sand contents caused the drop number to decrease in the free-fall drop impact test. From the uniaxial compression test, the compressive strength, elastic modulus, and toughness were calculated. The elastic modulus showed a better performance for samples with lower porosity. The compressive strength demonstrated higher values for samples with 15 wt.% sand contents than for samples with the other sand contents. The toughness values did not significantly change. It was evidenced that the porosity, mineral composition, and humidity exerted an influence during the mechanical tests. The mineral phases were analyzed by X-ray diffraction, and quantitative analysis based on whole-powder-pattern fitting revealed that the iron and titanium oxide contents increased as the concentration of sand in the pellets increased.

Determination of Impact Damage in CFRP via PVDF Signal Analysis with Support Vector Machine.

Carbon fiber reinforced plastics (CFRPs) have high specific stiffness and strength, but they are vulnerable to transverse loading, especially low-velocity impact loadings. The impact damage may cause serious strength reduction in CFRP structure, but the damage in a CFRP is mainly internal and microscopic, that it is barely visible. Therefore, this study proposes a method of determining impact damage in CFRP via poly(vinylidene fluoride) (PVDF) sensor, which is convenient and has high mechanical and electrical performance. In total, 114 drop impact tests were performed to investigate on impact responses and PVDF signals due to impacts. The test results were analyzed to determine the damage of specimens and signal features, which are relevant to failure mechanisms were extracted from PVDF signals by means of discrete wavelet transform (DWT). Support vector machine (SVM) was used for optimal classification of damage state, and the model using radial basis function (RBF) kernel showed the best performance. The model was validated through a 4-fold cross-validation, and the accuracy was reported to be 92.30%. In conclusion, impact damage in CFRP structures can be effectively determined using the spectral analysis and the machine learning-based classification on PVDF signals.

A novel scissor-type anti-shock seat employing rotary magnetorheological damper

In order to improve the cushioning performance of anti-shock seat in an impact environment and protect the lives of occupant to the greatest extent, the cushioning performance of a new type of anti-shock seat combining a rotary magnetorheological (MR) damper and a scissor seat was studied. Aiming at the “bottoming out” characteristic of scissor seats after the cushioning stroke is exhausted, and the dynamic model of scissor seats with MR damper is established. In order to test the cushioning performance of the new anti-shock seat in an impact environment, a prototype MR damper was processed and assembled, and the cushioning performance of the seat under different impact speeds was tested using a drop impact test platform. The test results show that the new anti-shock seat can adjust the cushion stroke and cushion force value to keep the acceleration limit of the occupant within the tolerance range, thereby effectively reducing the risk of injury.

The effect of two-step surface treatment by hydrogen peroxide and silanization of flax/cotton fabrics on epoxy-based laminates thermomechanical properties and structure

The epoxy composites reinforced with flax/cotton fibers subjected to two surface treatments were prepared by hand lay-up method. Flax/cotton fabrics were subjected to bleaching using hydrogen peroxide, silanization, and two-step modification consisting of both methods. The effects of these treatments were assessed by Fourier Transform Infrared Spectroscopy (FTIR) and the fabric color was examined with accordance to CIELab method. The produced composites were subjected to the assessment of mechanical properties using static tensile and flexural tests. Moreover, impact resistance was evaluated by drop impact tests and the Charpy method. The effect of surface treatment of flax/cotton fabrics on epoxy-based composites thermomechanical properties were studied using dynamic thermomechanical analysis (DMTA) and related to structural changes investigated with scanning electron microscopy (SEM). The realized research showed that the use of a two-stage surface modification of fibers allows the production of composites with increased interfacial adhesion, as well as enhanced mechanical properties in comparison to materials manufactured using unmodified fabrics.

Fabrication of robust self‐cleaning superhydrophobic coating by deposition of polymer layer on candle soot surface

AbstractA facile and inexpensive way have been developed to fabricate robust self‐cleaning superhydrophobic coating by depositing polymer layer on candle soot (CS) surface using dip coating method. The stability and robustness of the CS deposited superhydrophobic surface is much weaker due to weak interaction and nonchemical bonding with the substrate. We introduced a thin layer of polystyrene, polyethylene, polypropylene (PP), and polyvinylidene fluoride on CS surface in order to improve its mechanical properties. The fabricated surfaces with the use of respective polymers exhibited water contact angles of nearly 170, 174, 175, and 171° with sliding angles of 2, 1, 1, and 3°, respectively. Although, all the polymers used in this work exhibited excellent superhydrophobic and self‐cleaning surface property, we found that the PP deposited CS surface exhibit better stability against water jet hitting and water drop impact tests. The PP deposited CS surface almost maintained their surface properties even after 50 cycles of sandpaper abrasion and 20 cycles of adhesive tape peeling tests. The mechanical durability tests confirmed that PP is a better polymer to improve the long‐term durability of CS surface. Therefore, this simple, time saving, and inexpensive method for fabricating superhydrophobic coating can be used for potential industrial application.

Application of air-bubble cushioning to improve the shock absorption performance of type I industrial helmets

The industrial helmet is the most used and effective personal protective equipment to reduce work-related traumatic brain injuries. The Type I industrial helmet is a basic helmet model that is commonly used in construction sites and manufacturers. The purpose of the current study was to investigate if shock absorption performance of these helmets could be improved by using an air-bubble cushioning liner to augment the helmet’s suspension system. Drop impact tests were performed using a commercial drop tower test machine according to the ANSI Z89.1 Type I drop impact protocol. Typical off-the-shelf Type I industrial helmets were utilized in the study. The effects of the air-bubble cushioning on the helmets’ shock absorption performance were evaluated by comparing the original off-the-shelf helmet samples to the helmets equipped with an air-bubble cushioning liner. The air-bubble cushioning liner (thickness 5 mm) was placed between the headform and the helmet when being tested. The impactor had a mass of 3.6 kg and was free-dropped from different heights. The maximal peak transmitted forces for each of the tests have been evaluated and compared. Our results show that the shock absorption effectiveness of the air-bubble cushioning is dependent on the magnitude of the impact force. At lower drop heights (h<1.63 m), the air-bubble cushioning liner has little effect on the transmitted impact forces, however, at higher drop heights (h⩾1.73 m) the air-bubble cushioning liner effectively reduced the peak transmitted forces. At a drop height of 1.93 m (the highest drop height tested), the air-bubble cushioning liner reduced the peak transmitted force by over 80%. Our results indicate that adding an air-bubble cushioning liner into a basic Type I industrial helmet will substantially increase shock absorption performance for large impact forces.

Comparative Study on Reliability and Advanced Numerical Analysis of BGA Subjected to Product-Level Drop Impact Test for Portable Electronics

In this paper, drop reliability of various PBA (printed board assembly) mounting structures is investigated and compared. Then, we built SAC305 (Sn3.0Ag0.5Cu) interconnects for BGA (ball grid array) package failure model to evaluate the drop impact reliability of handheld devices. In order to simulate actual behavior of the solder joint under the drop impact load of handheld devices, we perform explicit full FEA (finite element analysis) modeling. However, this takes a lot of computing time because of the large aspect ratio of element size between solder joints and other structures such as PCB (printed circuit board) and electronic packages. Therefore, an effective way to represent solder interconnects for FEA is needed which would be relatively simpler yet detailed. Comparable board-level drop tests are conducted after equipping test vehicles with various fixtures considering PBA mounting structures, which make it possible to apply different loading conditions to BGA packages. The results show different drop impact life for solder interconnects depending on the mounting design of the PBA. Particularly, the solder interconnect of the component located at the middle of the PCB exhibits the shortest impact life where the highest tensile stress occurs. Also, the mounting design restraining PBA deflections shows better reliability under the drop impact loading. Sequentially, simulating with a PBA composed of the BGA package and the PCB is considered to assess the feasibility of the solder ball failure modeling when the drop impact load is applied. Especially, for the modeling of the solder balls, detailed solid model and simple beam model are compared regarding computational efficiency and numerical accuracy. We found that the simple beam model significantly shortens computational time from 110 h to less than an hour. Accordingly, the feasibility of the beam model for the solder balls is shown by correlating the stress level and the drop impact life obtained from the experiments.

Simple estimation method for strain rate sensitivity based on the difference between the indentation sizes formed by spherical-shaped impactors

The Johnson-Cook (JC) flow stress model is widely used in finite element analysis (FEA) in various fields to express the deformation behavior of metallic materials under high strain rate conditions. There is a need to facilitate an easier estimate of the JC parameter C, which is a material constant in the JC model associated with strain rate sensitivity. In this study, a simple estimation method for the JC parameter C, based on the difference between the indentation sizes formed by two spherical-shaped impactors, was proposed. The proposed method allows us to estimate the JC parameter C only by measurement of the indentation sizes formed via a high-velocity impact test, a drop impact test, or an indentation test. The fundamental equation was theoretically derived based on the energy conservation during the impact process of the impactor and the expanding cavity model, combined with the JC model and the equation of thermal conduction. To validate the proposed method, FEA was conducted using ten types of target materials under five impact velocity conditions, from 6 × 10−6 to 180 m/s. Based on the indentation depths obtained from FEA, the JC parameter C was estimated and compared with that input into FEA. As a result, it was confirmed that the estimated C is in agreement with that input into FEA within the relative errors of 10% under all impact velocity and target material conditions, except the target material of Ti6Al4V. From the results, it was demonstrated that the proposed method can easily estimate the JC parameter C, that is, the strain rate sensitivity, in the wide range of strain rate from 102 to 105 s−1.

Investigation of PDC Cutter Structural Integrity in Hard Rocks

Summary Robustness of round and V-shaped polycrystalline diamond compact (PDC) cutters against mechanical and thermal load was evaluated. Forensic analysis was used to estimate the range of loads and depths of cut (DOC) that cause structural overload of PDC cutters. Finite-element analyses (FEAs) were calibrated against these data and used to estimate the integrity of cutters. Thermal-abrasive wear was tested with single cutter tests on Sierra White granite with and without cooling for multiple material grades. The axial and tangential impact resistances were evaluated with drop and front face impact tests. In addition, full-scale laboratory drilling tests were conducted in granite [unconfined compressive strength (UCS) = 28,000 psi] and quartzite (UCS = 56,000 psi). Finally, failures for round and V-shaped cutters were evaluated in field trials. The V-shaped cutters scored similar to baseline cutters in thermal-abrasive tests but lower in axial impact tests. They also failed at 13 to 18% lesser tangential load. By accounting for 16% reduction in contact area between the shaped cutter and load anvil, it was concluded that both cutter geometries fail essentially at the same stress. In all full-scale tests, round cutters failed before the shaped cutters. This was in contrast with drop tests and is attributed to the shaped cutter's cutting efficiency, resulting in lesser load on the cutters for the same rate of penetration (ROP). The results were compared with field runs in hard and interbedded application in Oklahoma and west Texas. The conclusion based on FEA, laboratory, and field data was that in most cases, this shaped cutter shows the same or better dull as its base grade.

Towards an Acoustic Simulation of a Water Drop Impacting in a Water Pool

The sound which is produced when a water drop impacts into a water pool is a prominent example for acoustics produced by multiphase flow. In this work the feasibility of numerical methods for simulating this challenging test case is evaluated. First the multiphase flow needs to produce the correct physical mechanisms, e.g. the bubble entrapment. For this an in-house block-structured finite-volume solver with the volume-of-fluid method is used. For the curvature computation a standard finite difference method within the continuum surface force model is employed, including some necessary improvements. A high resolution in space and time is essential and therefore the method is parallelized by domain decomposition. The acoustic part is simulated with the linearized Euler equations which are valid in each phase but need to be adapted in the interface region. The results are compared with numerical and experimental data. It is shown, that the methods are suitable for simple test cases. A coupled drop impact test case corresponds with equivalent experiments until the drop detachment. The acoustic pressure shows a significant rise in the vicinity of the bubble detachment within both phases. However, an oscillation of the cavity bottom can not be observed in the multiphase neither in the acoustic outputs of the airborne signal.

Dynamic compressive behavior of rigid polyurethane foam with various densities under different temperatures

In this study, the effects of density, temperature, and impact energy on the dynamic behavior of polyurethane foam (PUF) were experimentally investigated. PUF is used as the primary insulation material in liquefied natural gas (LNG) insulation systems because it has several advantageous properties. LNG insulation systems require structural stability under impact loads, such as sloshing. For the safe design of insulation systems, the impact characteristics of the foam should be considered. Therefore, in this study, the density, temperature, and impact energy were selected as variables, and a series of drop impact tests was conducted on PUF. The typical damage mechanism of PUF was investigated by scanning electron microscopy, and the mechanical properties and absorbed energy as functions of the variables were compared and evaluated. As a result, we found that the dynamic behavior of the foams significantly depends on density, temperature, and impact energy. Moreover, at a relative density exceeding 0.12 (150 kg/m3), the foams exhibit the best mechanical properties. In conclusion, this study can be used to determine the optimum polyurethane density depending on the changing LNG insulation system requirements.

The effect of coal bottom ash in mechanical and environmental performances for polymer composite

Fabrication is essentially the manipulation of raw materials into a desired product based on a workable approach. In this project, fabrication is fundamentally the process by which coal bottom ash (BA) are compatible with resin to form and improve construction materials which satisfy the assigned requirements and applications. BA have a porous and granular structure which limits its application and commercialization. Many investigations have been carried out towards the effective utilization of other reinforcement material or fillers such as fly ash for both concrete composite and polymeric composites. From this research project, resin was used as binder materials to BA which have porous and granular structure that limits its application. Despite of that, the resin can be transformed and tailored to fit specific needs. The findings show resin was greatly cooperated more than 40% of BA in the mixture which directly improve the mechanical performances on drop impact test. A part from that, environmental issues should be considered in utilizing BA. Since the BA is classified under scheduled waste (SW 104) which contains heavy metals, CBA blended with resin were readily in encapsulation form to mitigate the leaching of metals towards surrounding. Leachate study was conducted to all sample compositions and there is no leaching of metals detected from the sample due to increase in chemical stability. The concentration of toxic metals that leached were below than threshold value set by Department of Environment, Malaysia (DoE).

Drop Impact of Closed-Cell Aluminum Foam: Experiment and Simulation

Fall drop impact test for closed-cell aluminum foams were conducted experimentally and numerically. Deformation mechanisms at the cell level were discussed. The deformation mechanisms of cells were investigated and a novel FE model was proposed. Our model is combination of cellular part in the middle and solid part with the mechanical property of the same foam to adopt boundary condition correctly in order to reduce run time.

Correlation between Drop Impact Energy and Residual Compressive Strength According to the Lamination of CFRP with EVA Sheets.

Carbon-fiber-reinforced plastic is an important building material; however, its application is limited because of its brittleness, leading to vulnerability under shock. Thus, the strength performance of carbon-fiber-reinforced plastics needs to be improved. Here, the drop impact test was conducted to analyze the impact energy and fracture characteristics of carbon-fiber-reinforced plastics and ethylene vinyl acetate sheets. The compression after impact test was performed to assess the residual compressive strength. The thermal energy generated was measured as change in temperature at the time of fracture to investigate the relationship between thermal and mechanical properties. The impact absorption efficiency of 100% was achieved when the carbon-fiber-reinforced plastics specimen was laminated with four or more sheets of ethylene vinyl acetate. The thermal energy generated during impact, the impact load, and the compression after impact test strength was reduced with the increasing number of laminated ethylene vinyl acetate layers. Our results showed that, by carefully selecting the optimal conditions of fabricating the carbon-fiber-reinforced plastic/ethylene vinyl acetate composites, carbon composite materials can be used for impact mitigation.