Free-fall Impact Research Articles

ISRM Suggested Method for Determining the Properties of Rock Bolt Assemblies by Mass Freefall Impact Testing in the Laboratory

AbstractThis Suggested Method proposes impact tests to determine selected properties of full-scale rock bolt assemblies subject to an axis-aligned impact force. These properties include the stiffness of the bolt assembly, the rise time, the tensile strength, the ultimate displacement, and the energy absorption of the rock bolt assembly. These properties may be used to design or select ground support for burst-prone ground conditions. This Suggested Method is limited to the mass freefall impact test method. It is performed using a test frame in the laboratory. The Method specifies the requirements for the testing apparatus and measurement sensors, the test procedures, the data processing methods and the reporting items.

Topical application of daphnetin hydrogel for traumatic brain injury.

Traumatic brain injury (TBI) causes neuronal cell damage and dysfunction. According to previous studies, daphnetin (Dap) has a protective effect in neurological injury. However, the in vivo bioavailability of daphnetin is not high. The purpose of this study was to determine whether administering daphnetin directly into the site of injury via a hydrogel drug carrier could improve its therapeutic impact. Tripolycerol monostearates / daphnetin (TM/Dap) hydrogels were prepared and characterised using water bath heating, scanning electron microscopy (SEM) and small animal in vivo imaging techniques. The TBI model was established using the Feeney free fall impact method. Using the Morris water maze test, the mNSS neurological deficit rating scale, haematoxylin-eosin staining, and liver and kidney function tests, the therapeutic benefit of TM/Dap and its toxic side effects were assessed. The therapeutic effects of TM/Dap were further investigated using wet and dry gravimetric methods, Evans blue staining, protein immunoblotting, immunofluorescence staining techniques and ELISA. The efficacy of the TM/Dap hydrogel in gradually releasing daphnetin in the context of traumatic brain damage was shown by both in vitro and in vivo tests. Behavioral experiments showed that the learning and spatial memory abilities of TM/Dap hydrogel treated mice were significantly improved in the water maze experiment. And TM/Dap hydrogel has high biosafety for organisms. The results of the therapeutic mechanism of action showed that TM/Dap hydrogel showed more significant efficacy in reducing the neuroinflammatory response caused by TNF-α, IL-6 and other factors, as well as promoting the recovery of post-traumatic neurological function. The use of hydrogel as a drug carrier for daphnetin showed more significant efficacy in reducing neuroinflammatory response, protecting nerve tissue and promoting post-traumatic neurological recovery compared with traditional drug delivery methods.

Design and experiment of the simulated electronic corn ear based on UWB/IMU technology

In order to explore kinematic and dynamic parameters of corn ear in the process of threshing, and reveal threshing principle and grain impact damage mechanism, a simulation electronic corn ear was designed based on ultra wide band (UWB) and inertial measurement unit (IMU) technology. The spatial positioning algorithm and impact force analysis algorithm of electronic corn ear were studied, and a simulated threshing test bench was built. Then free fall impact force detection test and comprehensive performance test of the electronic corn ear were carried out. The experimental results showed that the average detection error of free fall impact force was about 0.69 N, with an accuracy more than 95 %, and the average detection error of impact force in the process of simulation threshing was about −0.27 N, with an accuracy more than 97 %. The spatial positioning accuracy of electronic corn ear was related to the number, layout and positioning algorithm of UWB positioning base station. Unscented kalman filter (UKF) tight combination positioning algorithm had the highest positioning accuracy (about 100 % probability of positioning error within ± 0.15 m) under the condition of non-line of sight (NLOS) (5 base stations, 3.2 m height difference). Extended kalman filter (EKF) tight combination positioning algorithm had the second highest positioning accuracy (about 100 % probability of positioning error within ± 0.2 m), followed by kalman filter (KF) loose combination, UWB single positioning and IMU single positioning algorithm. The results are helpful for obtaining kinematic and dynamic parameters in the process of ear threshing and separation, understanding the mechanism of efficient and low-damage threshing, and provide a basis for the segmented optimization design of subsequent devices.

Construction Design of the Floater Considering the Free-Falling Impact of the Floatplane on Calm Water

The floatplane-type aircraft is very suitable to be developed as a means of transportation connecting the scattered islands in Indonesia, as it has floats under the fuselage to make landings and operate on the water surface. In bad weather, a floatplane can lose lift, resulting in a free fall from an abnormal height and a violent collision between the floatplane structure and the water surface. Meanwhile, regulations require that the strength of the structure be able to withstand the impact load due to an emergency landing. This paper proposes a floater construction design for the N219 floatplane with three scantling variations of 5083 H321 aluminium material that considers the total payload and take-off weight. The magnitude of the impact load on the bottom of the float with the water surface in the case of free fall at 0.5 m and 1 m height is predicted by the Wegner equation model at each cross section along the float. The magnitude of stress in each floater construction design is evaluated by the principle of the finite element method using commercial software. The simulation results show that all models have a maximum stress less than permissible stress and also maximum deformation is unsignificant.

Anacardic acid improves neurological deficits in traumatic brain injury by anti-ferroptosis and anti-inflammation

BackgroundTraumatic brain injury (TBI) is an important cause of disability and death. TBI leads to multiple forms of nerve cell death including ferroptosis due to iron-dependent lipid peroxidation. Anacardic acid (AA) is a natural component extracted from cashew nut shells, which has been reported to have neuroprotective effects in traumatic brain injury. We investigated whether AA has an anti-ferroptosis effect in TBI. MethodsWe used the Feeney free-fall impact method to construct a TBI model to investigate the effect of AA on ferroptosis caused by TBI, in which Ferrostatin-1 (Fer-1), a ferroptosis inhibitor, served as a positive control group. We first identified the therapeutic effect of AA on TBI through modified neurological severity score (mNSS) and determined the appropriate concentration. Secondly, we investigated the effect of AA on the expression level of the key protein of ferroptosis by Western blotting and immunohistochemistry. Then the effect of AA on nerve tissue injury and nerve function improvement was verified. Finally, enzym-linked immunosorbent assay (ELISA) was used to verify that AA could reduce inflammation after TBI. ResultsWe found the intensely inhibitory effect of AA on ferroptosis, which is in parallel with the results obtained after Fer-1 treatment. In addition, AA and Fer-1 mitigated TBI-mediated tissue defects, destruction of the blood-brain barrier, and neurodegeneration. Novel object recognition (NOR), mNSS and water maze test showed that AA could significantly reduce the impairment of neural function and behavioral cognitive ability caused by TBI. Finally, we also demonstrated that AA has not only an anti-ferroptosis effect, but also an anti-inflammation effect. ConclusionsAA can reduce the neurological impairment and behavioral cognitive impairment caused by TBI through the dual effect of anti-ferroptosis and anti-inflammation.

Design of A High-Precision Component-Type Vertical Pendulum Tiltmeter Based on FPGA.

This paper presents a high-precision component-type vertical pendulum tiltmeter based on an FPGA (Field Programmable Gate Array) that improves the utility and reliability of geophysical field tilt observation instruments. The system is designed for rapid deployment and offers flexible and efficient adaptability. It comprises a pendulum body, a triangular platform, a locking motor and sealing cover, a ratiometric measurement bridge, a high-speed ADC, and an FPGA embedded system. The pendulum body is a plumb-bob-type single-suspension wire vertical pendulum capable of measuring ground tilt in two orthogonal directions simultaneously. It is installed on a triangular platform, sealed as a whole, and equipped with a locking motor to withstand a free-fall impact of 2 m. The system utilizes a differential capacitance ratio bridge in the measurement circuit, replacing analog circuits with high-speed AD sampling and FPGA digital signal processing technology. This approach reduces hardware expenses and interferences from active devices. The system also features online compilation functionality for flexible measurement parameter settings, high reliability, ease of use, and rapid deployment without the need for professional technical personnel. The proposed tiltmeter holds significant importance for further research in geophysics.

Tests on Hydraulic Props Equipped with Yield Valves at Dynamic Load Modelling a Rock Burst

The article presents the results of tests on SHC-40 hydraulic props equipped with two types of valve blocks: standard (with spring steel cylinder) and BZG-2FS (with gas spring). The research was conducted using impact mass of 4,000 kg and with extreme dynamic load of free fall impact mass of 20,000 kg released from different heights h. The dynamic tests involved a camera with the speed of image capture up to 1,200 frames/sec, which made it possible to register the stream of liquid at the dynamic load and to determine the valve opening time. The study conducted on SHC-40 NHR10 props equipped with two types of valve blocks: a standard and the BZG-2FS fast acting relief, showed that the prop with the BZG-2FS block is more suitable and more effective in the case of areas with high risk of mining tremors and rapid stress relief of a seam. Research methodology developed in the Central Mining Institute combines digital recording technique of pressure in a prop and fast registration of the images, and allows to acquire more accurate analysis of dynamic phenomena in the prop during testing.

Effects of electroacupuncture on neurological function and expressions of p-JNK and Beclin-1 in traumatic brain injury rats

To observe the effect of electroacupuncture (EA) on neurological function, the expressions of phosphorylated c-Jun amino terminal kinase (p-JNK) and Beclin-1 in rats with traumatic brain injury (TBI), so as to explore the underlying mechanism of EA in the treatment of TBI. A total of 64 SD rats were randomly divided into blank, sham, modeling groups, with 8 rats in the blank group and the sham group and 48 rats in the modeling group. The modified Feeney free-fall impact method was used to establish the TBI rat model. After modeling, rats of the modeling group were randomly divided into model and EA groups, which were further divided into 3 d, 7 d and 14 d subgroups with 8 rats in each group. Rats in the EA group were treated with acupuncture at "Baihui" (GV20, retained for 15 min), "Shuigou" (GV26, stabbed for 20 s), "Neiguan" (PC6) and "Zusanli" (ST36) of the right side. EA (2 Hz, 1 mA) was applied to PC6 and ST36 for 15 min. The above treatments were performed once a day, and different subgroups were continuously stimulated for 3, 7 and 14 days, respectively. The neurological impairment was evaluated by modified neurological severity score(mNSS). The pathological morphological changes and the protein expressions of p-JNK and Beclin-1 in the injured area of the brain were detected by Nissl staining and immunohistochemistry, separately. After modeling, the mNSS and the protein expressions of p-JNK and Beclin-1 were increased (P< 0.05) on day 3, 7 and 14 in the model group relative to the sham group. The Nissl bodies were reduced or even dissolved and neurons were seriously damaged in the model group on the 3rd day, which were mildly repaired on day 7 and 14. Following acupuncture interventions, compared with the model group, the mNSS on day 7 and 14 and the protein expressions of p-JNK and Beclin-1 on day 3, 7 and 14 were decreased (P< 0.05)in the EA group. The status of Nissl bodies and neurons in the EA group was better at all time points than that in the model group. There were no significant differences in the above indicators between the blank group and the sham group. EA can significantly improve the neurological function of TBI model rats, which may be related to its effects in down-regulating the protein expressions of p-JNK and Beclin-1 in the injured area of the brain.

Impact response prediction of square RC slab of normal strength concrete strengthened with (1) laminates of (i) mild-steel and (ii) C-FRP, and (2) strips of C-FRP under falling-weight load

Reinforced concrete (RC) slab is an indispensable component of all kinds of structures to carry gravity loads in general. Quite often than not, the slabs are subjected to impact loads from accidental mishaps, falling construction equipment, and falling boulders and rocks which are not considered in the structural design. Design codes of practice for RC structures permit the structural design based on the experimental investigation which is not viable because of constraints such as experimental facilities, materials, and time requirements. However, current advancements in the computational techniques available make it possible to obtain the comprehensive response of the slabs subjected to impact loadings. In the present research work, different strength-enhancing techniques such as steel/C-FRP sheet laminates and C-FRP strips are considered for impact resistance enhancement of two-way normal strength concrete slab, 1000 mm × 1000 mm × 75 mm, with 0.88 % conventional tension steel reinforcement subjected to a free-falling concentrated load of 1035 N. For this purpose, a 3-D finite element model of impacting test setup is formed in ABAQUS-v.6.15 explicit commercial computer code. Computational analyses and simulations of free-fall impact are carried out on the validated ABAQUS model by allowing a 105 kg steel weight (impactor) from a height of 2500 mm with an initial impacting velocity of 7 m/ sec on the top surface of the slab at its centroid. The Concrete Damage Plasticity model is implored for nonlinear elastic and inelastic behaviors, degradation of stiffness, and loading rate effect on concrete. The nonlinear behavior of the reinforcing bars is taken into account. Steel is idealized with the Johnson-Cook model but the C-FRP laminate is defined or modeled with ABAQUS Hashin’s criterion. It is found that the used strengthening techniques improve the response of the slab in terms of displacement and damage severity, and alter the mode of failure.

Ultra high performance concrete and C-FRP tension Re-bars: A unique combinations of materials for slabs subjected to low-velocity drop impact loading

In this research work, different combinations of normal strength concrete (NSC), ultra-high-performance concrete (UHPC), and steel fiber-reinforced UHPC (SFR-UHPC) concrete with re-bars of conventional steel and of carbon fiber-reinforced polymer (C-FRP) are used in a two-way square slab of size 1000mm x 1000mm x 75mm subjected to 2500 mm free-fall impact loading. Experimental arrangement consisting of 105 kg dropping weight with the circular flat impacting face of 40 mm diameter used for carrying out impact test is modeled using a high-fidelity physics-based finite element computer code, ABAQUS/Explicit-v.6.15. After validating the experimental results of the NSC slab with steel bars, analyses are extended by replacing NSC and steel bars with UHPC/SFR-UHPC and C-FRP bars, respectively, under the same dropping weight. Only the remote face (tension face) of the slabs is provided with the re-bars. Widely employed and available with the ABAQUS, the Concrete Damage Plasticity model with strain-rate effects has been entrusted for simulating the concrete plastic response. Re-bars of steel are idealized with the Johnson-Cook plasticity damage model. C-FRP re-bars are defined with the classical plasticity model following the elastic-plastic constitutive laws. The impact responses of the slabs consisting of NSC/UHPC/SFR-UHPC concrete with re-bars of steel, and C-FRP combinations considered are discussed and compared. Slabs made of UHPC/SFR-UHPC concrete with the C-FRP re-bars are found to offer a promising combination of materials to withstand low-velocity impact load with little damage and extraordinary impact performance.

An experimental study of 3D printing based viscoelastic bimaterial subjected to low-velocity impact

In this paper, a bimaterial composite consists of a stiff 3D printed frame and a soft viscoelastic foam is investigated for impact protection applications. Samples of the base materials, frames, and bimaterials with two different volume fractions were subjected to free fall impact at different impact velocities. The data from an accelerometer and a high-speed camera were analyzed to obtain the impact force, deformation, and energy dissipation. The experimental results showed that the impact force and deformation are inversely related, and the bimaterial composite can be a good compromise solution. The energy dissipation of the bimaterial, however, is reduced when compared with that of the base materials. The results also show that for the present lattice frame structure, increasing the volume fraction of the frame material can reduce displacement and energy dissipation but increase impact force. This phenomenon indicates the potential of tuning the attributes of bimaterial, such as the base material property and the 3D printed frame geometry, for improved impact protection performance.

Measurement Method of Collision Restitution Coefficient between Corn Seed and Soil Based on the Collision Dynamics Theory of Mass Point and Fixed Surface

The collision restitution coefficient (CRC) is the essential parameter of the discrete element method (DEM) to study the interaction mechanism between corn seed and soil. The accuracy of its measurement results is the criticalness to ensuring simulation accuracy. In the current study, the CRC between corn seed and soil is mainly measured by the method of corn seed colliding with soil. However, since the soil is a granular body, the essence of the collision of corn seed with soil is the collision between one corn seed and a quantity of soil particles, resulting in inaccurate measurement results soil particles. Therefore, based on the collision dynamics theory of mass point and fixed surface, this paper proposed a measurement method of CRC to study the interaction mechanism between corn seed and soil. This paper analyzed the influence of mass point selection on the measurement results of CRC in the collision process. The measurement method was determined by taking soil particle as mass point and corn seed as fixed surface. To verify the feasibility of this method, a CRC measurement system was established based on high-speed camera technology. The soil particle was dropped at the heights of 10, 15, 20, and 25 cm to collide with the corn seed. The separation velocity and approaching velocity of the soil particle was measured to obtain the CRC between the corn seed and soil. Taking the CRC as the essential parameter of discrete element simulation, the discrete element simulation experiment (DESE) and the soil bin experiment (SBE)of corn seed free fall impact on soil were carried out, and the experiment results were compared and analyzed. In the experiment, the falling height (40, 50, 60, 70 cm) of corn seed and the touching position of the corn seed (positions a, b, c, d) were taken as the influencing factors. The movement state of corn seed and the separation approaching velocity ratio (SAVR) ξ during the collision were taken as the indexes. The results showed that when the positions of corn seed touched the soil was the same, with the increase of the falling height, the SAVR ξ obtained from the DESE and the SBE showed a downward trend. When the falling height was the same, and the corn seed touched the soil at positions b, c, and d, the motion state in the DESE was basically the same as that in the SBE. The relative error of the SAVR between the DESE and the SBE was less than 10%, which proves the feasibility of the method proposed in this paper. The measurement method of the CRC between corn seed and soil proposed in this study provided a theoretical research basis for clarifying the interaction mechanism between corn seed and soil and solving the seed bouncing in high-speed precision sowing.

Constitutive modelling of non-cohesive soils under high-strain rates: a consistency approach

Rapid loading of sands is a common issue in geotechnical engineering problems such as projectile or free-fall impact. At high strain rates (HSR), soils show more strength and enhanced dilation (viscoplastic behaviour) compared to the response at low rates (inviscid behaviour). However, few constitutive models account for the viscoplasticity of sands. Hence, the development of viscoplastic models is highly desired. Usually, viscoplasticity is modelled using overstress methods. However, overstress methods impose an overall modification of the constitutive equations, which prevents control of the evolution of internal state variables and the enforcement of the consistency condition. In this study, a generalised consistency–viscoplasticity method is proposed and applied to a non-associative modified Mohr–Coulomb model with coupled stress–dilation relation. The influence of strain rate is incorporated using a work–energy approach by way of an inertial coefficient. Two explicit integration strategies are proposed and compared, and guidelines for their implementation are shared. The numerical response of the model is tested by using drained triaxial simulations under constant axial strain rate, relaxation and impact loading. The results indicate that the consistency–viscoplasticity is a feasible alternative to simulate soil behaviour under HSR, capturing reasonably well the observed experimental responses.

Study Of Helmet Toughness In Rafting Fiberglass And Talk Reinforced Epoxy Composite Materials With Impact-Free Fall Method

Fiberglass is an alloy or a mixture of several chemicals (composite materials) that react and harden within a certain time. This material has several advantages over metal materials, including: lighter, easier to shape, and cheaper. Based on the static tensile test, the average tensile strength of the three-layer composite reinforced with woven, random, and talc glass fiber in the three composite test specimens was 50.7970 MPa for composition 1, 52.7684 MPa for composition 2, and 52.7684 MPa for composition 2. composition 3 of 53.6094 MPa. Based on the bending test, the average impact strength of the three composite test specimens is for composition 1 of 39.4805 MPa, composition 2 of 33.3044 MPa, and composition 3 of 53.8329 MPa. of the three compositions, composition 3 is better because it has a higher test value than the other two compositions. From the simulation results, the impact stress for the top is 7.05 MPa, for the front is 5.77 MPa and the side is 4.66 MPa. And from the results of comparing the stress from the free fall impact simulation results with the experimental free fall impact test for the above test, the simulation results are 7.05 MPa and the experimental results are 7.06 MPa, then the difference is 0.01 MPa (0.14%), for For the front test, the simulation results are 5.77 MPa and the experimental results are 5.12 MPa, so the difference is 0.65 MPa (11.26%), and for the side test, the simulation results are 4.66 MPa and the experimental results are 4.04 MPa, so we get difference of 0.62 MPa (13,3%). The amount of impact energy absorbed by a rafting helmet with a flat plate anvil is 729.

Impact of free Fall Impact versus Treadmill Physical Exercise Programs: Which is Most Osteogenic?

Exercise plays a key role for bone remodeling throughout our lives. Within bone cells, osteocytes have the ability to translate mechanical stimuli to bone anabolic cellular signaling. A variety of protocols have been used to apply both direct and indirect stimuli to bone. Herein, we compared running and free fall impact exercise protocols and their effects on markers of osteogenesis and bone strength.

Restoration of dynamic characteristics of RC T-beams exposed to fire using post fire curing technique

This paper presents experimental results of structural performance and dynamic characteristics of fire-damaged reinforced concrete (RC) T-beams subsequently repaired using the technique of post-fire curing. A total of six specimens were cast, two were unheated specimens, four specimens were exposed to 900 °C furnace temperature for 1 h. Two of the heated specimens were re-cured in water for 28 days. The dynamic characteristics such as frequency and damping were determined by exciting the beams using the free fall impact test. The beams were also subjected to load tests for strength and stiffness evaluation. Experimental results from load tests showed that T-beams lost approximately 40% strength and 33% stiffness when exposed to elevated temperatures. After post-fire curing, the beams regained almost 90% of their strength and stiffness. The loss of frequency in percent was found to be very similar to the stiffness values from load tests. The analytical modelling of the frequencies for undamaged, fire-damaged and repaired beams was carried out using lumped mass approach. The analytical and experimental results were found to be in good agreement. The change in dynamic characters due to fire damage is found to be an important factor, ignored in previous studies. All the beams exhibit failure in flexure during the third point loading test.

Free-fall landing and interval running have different effects on trabecular bone mass and microarchitecture, serum osteocalcin, biomechanical properties, SOST expression and on osteocyte-related characteristics.

The effects of treadmill interval training (IT) and free-fall exercise were evaluated on bone parameters including osteocyte related characteristics. Thirty-eight 4-month-old male Wistar rats were randomly divided into a control (C) group and exercise groups: IT, 10 free-fall impacts/day with a 10-s (FF10) or 20-s interval between drops (FF20), 5 days/week, for 9 weeks. We assessed bone mineral density (BMD); microarchitecture by µCT; mechanical strength by a 3-point bending test; density and occupancy of the osteocyte lacunae by toluidine blue staining; osteocalcin and NTx systemic levels by ELISA; and bone tissue Sost messenger RNA (mRNA) expression by RT-PCR. NTx levels were significantly lower in exercise groups as compared with the C group. In exercise groups the Sost mRNA expression was significantly lower than in C. Tb.N was significantly higher for IT and FF20 compared with the C group. Tb.Sp was significantly lower in FF10 compared with the C group. Both IT and FF20 were associated with higher tibial lacunar density as compared with FF10. compared with FF10, IT fat mass was lower, while tibial osteocyte lacunae occupancy and systemic osteocalcin level were higher. All exercise modes were efficient in reducing bone resorption. Both IT and free-fall impact with appropriate recovery periods, which may be beneficial for bone health and osteocyte-related characteristics. Novelty: Interval training is beneficial for bone mineral density. Exercises decreased both bone resorption and inhibition of bone formation (Sost mRNA). Longer interval recovery time favors osteocyte lacunae density.

Numerical Simulation of Container Breach and Airborne Release of Solids Due to Mechanical Insults

Abstract Throughout U.S. Department of Energy (DOE) complexes, safety engineers employ the five-factor formula to calculate the source term (ST) that includes parameters of airborne release fraction (ARF), respirable fraction (RF) and damage ratio (DR). Limited experimental data on fragmentation of solids, such as ceramic pellets (i.e., PuO2), and container breach due to mechanical insults (i.e., drop and forklift impact), can be supplemented by modeling and simulation using high fidelity computational tools to estimate these parameters. This paper presents the use of Sandia National Laboratories' SIERRA solid mechanics (SM) finite element code to investigate the behavior of the widely utilized waste container (such as 7A Drum) subject to a range of free fall impact and puncture scenarios. The resulting behavior of the container is assessed, and the estimates are presented for bounding DRs from calculated breach areas for the various accident conditions considered. This paper also describes a novel multiscale constitutive model recently implemented in SIERRA/SM that simulates the fracture of brittle materials such as PuO2 and determines ARF during the fracture process. Comparisons are made between model predictions and simple bench-top experiments.

Static and Dynamic Performances of Chopped Carbon-Fiber-Reinforced Mortar and Concrete Incorporated with Disparate Lengths.

The impact load, such as seismic and shock wave, sometimes causes severe damage to the reinforced concrete structures. This study utilized different lengths of chopped carbon fibers to develop a carbon-fiber-reinforced mortar (CFRM) and carbon-fiber-reinforced concrete (CFRC) with high impact and anti-shockwave resistance. The different lengths (6, 12, and 24 mm) of chopped carbon fibers were pneumatically dispersed and uniformly mixed into the cement with a 1% weight proportion. Then the CFRM and CFRC specimens were made for static and dynamic tests. The compressive and flexural strengths of the specimens were determined by using the standard ASTM C39/C 39M and ASTM C 293-02, respectively. Meanwhile, a free-fall impact test was done according to ACI 544.2R-89, which was used to test the impact resistances of the specimens under different impact energies. The CFRM and CFRC with a length of 6 mm exhibit maximum compressive strength. Both flexural and free-fall impact test results show that the 24 mm CFRM and CFRC enhances their maximum flexural strength and impact numbers more than the other lengths of CFRM, CFRC, and the benchmark specimens. After impact tests, the failure specimens were observed in a high-resolution optical microscope, to identify whether the failure mode is slippage or rupture of the carbon fiber. Finally, a blast wave explosion test was conducted to verify that the blast wave resistance of the 24 mm CFRC specimen was better than the 12 mm CFRC and benchmark specimens.

Advanced utilization of 3D digital image correlation for thermal and impact reliabilities of electronics components

PurposeThis paper aims to present an adaptation of digital image correlation (DIC) to the electronics industry for reliability assessment of electronic packages. Two case studies are presented: one for warpage measurement of a micro-electro-mechanical system (MEMS) package under different temperature conditions and the other for the measurement of transient displacements on the surface of a printed circuit board (PCB) assembly under free-fall drop conditions, which is for explaining the typical camera setup requirement and comparing among different boundary conditions by fastening methods of PCB.Design/methodology/approachDIC warpage measurements on a small device, such as a MEMS package, require a special speckle pattern. A new method for the creation of speckle patterns was developed using carbon coating and aluminum evaporative deposition. To measure the transient response on the surface of a PCB during a free-fall impact event, three-dimensional (3D) DIC was integrated with synchronized stereo-high speed cameras. This approach enables the measurement of full-field displacement on the PCB surface during a free-fall impact event, contrary to the localized information that is obtained by the conventional strain gage and accelerometer method.FindingsThe authors suggest the proposed patterning method to the small-sized microelectronics packages for DIC measurements. More generally, the idea is to have a thin layer of the dark or bright color of the background and then apply the white or black colored pattern, respectively, so that the surface has high contrast. Also, to achieve a proper size of speckles, this paper does not want to expose the measuring objects to high temperatures or pressures during the sample preparation stage. Of course, it seems a complicated process to use aluminum evaporator, carbon coater and electroformed mesh. However, the authors intend to share one of the solutions to achieve a proper pattern on such small-sized electronic packages.Originality/value3D DIC technique can be successfully implemented for the measurement of micro-scale deformations in small packages (such as MEMS) and for the analysis of dynamic deformation of complex PCB.