Drop-weight Test Research Articles

Development of a Weight-Drop Impact Testing Method for Dental Applications.

For evaluating the impact strength of dental materials, the Izod test or Charpy test has been used, but specimen preparation for these tests is difficult due to the adjustment of a notch on them. By contrast, a weight-drop impact test does not require notched specimens. Therefore, it might be possible to measure the impact strength more accurately than conventional methods. This study aimed to establish appropriate conditions for applying the weight-drop impact test on small specimens of acrylic resin. To determine the most reliable impact fracture energy of acrylic resins, different diameters and thicknesses of PMMA resin specimens, diameters and weights of the striker, and diameters of the supporting jig were compared. For all specimen thicknesses, when the striker diameter was 6–10 mm, the impact fracture energy was constant when the inner diameter of the specimen-supporting jig was 8–10 mm. In addition, the measured E50% value was mostly equal to the median value of the impact fracture energy. Thus, for the weight-drop impact test, this method was effective for material testing of small specimens, by clearly specifying the test conditions, such as the thickness of disc-shaped specimens, the diameter of the striker, and the inner diameter of the specimen-supporting jig.

Impact resistance of CFRP-reinforced wood beams under axial force using a digital image correlation method

Drop-weight testing provided data on the dynamic impact–resistance properties of wood beams reinforced with carbon fiber reinforced polymers (CFRPs) and of unreinforced plain wood beams. Axial force was also applied on the beams to improve the impact-resistance ability of the beams. The digital image correlation (DIC) technique was used to obtain impact deformation. The test results of beam failure modes, impact force–time history curve, and impact deformation were used to analyze the impact-resistance properties. In addition, the impact strength and energy dissipation of wood beams under impact load were calculated. The results indicated that reinforcement has an obvious effect on the impact-resistance ability of wood beams and that the axial force has some reinforcing effect. The strengthening effect increases in the order of 1-ply CFRP sheet, CFRP plate, and 2-ply CFRP sheet.

CTOA Testing of Thick DWTT Specimens: Experiment and FEA Simulation for Development of an Annex for ASTM E3039

Abstract ASTM E3039-16, Standard Test Method for Determination of Crack-Tip-Opening Angle of Pipe Steels Using DWTT Specimens (superseded), is limited to drop-weight tear test (DWTT) specimens with thickness B in the range 6–20 mm. There is a trend in the pipeline industry toward heavier wall pipe in the range of 25-mm thickness; hence, there is a need to test thicker DWTT specimens for crack propagation resistance. To address this need, proportionally larger DWTT geometry is proposed to allow a larger steady-state region with the same analysis procedure as in ASTM E3039. To support the development of an E3039 Annex, tests of an X70 pipe steel with B = 26.8 mm were performed at quasistatic and intermediate rates. The critical crack-tip-opening angle (CTOAB/2) of 15.0° ± 1.7°, estimated according to ASTM E3039, was close to the CTOA of 14.7° measured at midthickness sections. The effect on CTOA of varying the loading rate between 5 × 10−5 m/s and 0.1 m/s was found to be negligible. Fracture surfaces of specimens interrupted during testing showed severe crack tunneling. Finite element analysis simulations of crack propagation using a damage-mechanics model were performed on standard and proportionally large DWTT specimens to derive and compare CTOAs. These results show that ASTM E3039 can be applied successfully with proportionally scaled specimens to measure CTOA for steels of thicknesses significantly larger than 20 mm.

Evaluation of Impact Resistance for Derailment Containment Provision Using Drop Weight Test

In Korea, to prepare for unexpected accidents caused by human errors and natural disasters that cannot be completely prevented, a protective wall (a type of side-structure) against derailed trains has been installed on high-speed railway bridges as one of the physical measures to mitigate the associated damage. However, taking the geometric aspects of a domestic railway bridge's super structure into consideration, such a protective wall is not appropriate, and the corresponding protective performance does not provide adequate security. Hence, a protective wall named Derailment Containment Provision (DCP) was newly developed and installed in the track gauge. In this study, to evaluate the impact resistance of the newly developed DCP, a drop weight experiment was conducted, and the impact behavior corresponding to a specific impact energy was analyzed.

Preliminary Evaluation of Carbon Dioxide, Oxygen, and Hydrogen for Promoting Chromite Liberation by Breakage

Mineral liberation is one of the primary objectives in comminution circuits for the downstream separation of valuable minerals. Breaking minerals through their grain boundaries (grain-boundary breakage) enables mineral liberation in their natural grain size, removing the need for intensive grinding. This study aimed to evaluate if gaseous carbon dioxide, oxygen, or hydrogen can be used as grinding additives to promote the liberation of chromite grains by grain-boundary breakage. For this purpose, chromite ore particles in the −9.53 + 6.35 mm size fraction were pretreated by exposing them to carbon dioxide, oxygen, or hydrogen flow. Then, the untreated and pretreated samples were broken in a drop-weight tester under the same conditions. Finally, the grade-recovery plots of chromite grains in the selected progeny size fractions and the overall progeny distributions were measured and compared. Pretreatment with carbon dioxide flow was found beneficial for grain-boundary breakage. It significantly enhanced the liberation of coarse chromite grains along with the overall progeny fineness. EPMA analysis showed that the adsorption of carbon dioxide seems to reduce aluminum concentration at grain boundaries, which could be the reason for grain-boundary weakening. These results suggest that carbon dioxide can be used as a grinding additive, reducing the carbon footprint of the mining industry.

Finite Element Analysis of Stress Wave Propagation in Adhesive Joints under Low Speed Impact Tensile Loadings

AbstractThe adhesive joints are suddenly disturbed by the impact loadings in industrial applications. The stress wave propagation and stress distribution in the single lap joint (SLJ) with aluminum alloy adherends and two types of epoxy adhesives under impact tensile loadings are analyzed with the finite element method (FEM) to simulate the drop weight test. The impact velocity is assumed below 2000 mm s−1 and the total impact history is 0.2 ms. The stress is observed throughout the middle plane in the overlap area. The stress wave propagation in the adhesive layer reveal obvious directivity and show the transformation from the elastic wave to the plastic wave. The equivalent Von‐Mises stress increases approximately linearly with the increase of impact energy. At different times, the equivalent Von‐Mises stress along the adhesive longitude present bimodal distribution, while the stress wave propagation characterizes the rising‐falling‐rising trend. The stress singularity area is around 3–5 mm from edges. The equivalent Von‐Mises stress of the transversal middle plane in the adhesive layer is sensitive to rupture with the symmetrical distribution. A damage sensitive area located 2.6 mm away from both edges. The upper interface of the adhesive layer may initiate failure under the low‐velocity impact.

Some Observations About the Drop-weight Explosive Sensitivity Test

The apparent simplicity of the drop-weight apparatus for explosive sensitivity testing hides the reality that it is actually a complex integrated test of both ignition and growth of deflagration. Although the drop-weight test is undeniably a useful screening test for explosive properties, a misunderstanding of the technique’s limitations has blinded many researchers to its limited wider applicability. This monograph discusses how the test actually works, the significant engineering difficulties with standardization between machines, which types of explosives are suited to the test and which are not, and finally offers a few suggestions for alternatives when a more quantified understanding of a material’s response is required for other applications.

Brittle Crack Arrestability and Inverse Fracture in DWTT

Abstract The drop-weight tear test (DWTT) has been widely used to evaluate the resistance of linepipe steels against brittle crack propagation, and the shear area fraction SA% in the DWTT has been adopted in the requirement for the linepipe steels. However, recent studies have pointed out the issue of ambiguity in evaluation of the DWTT when a ductile crack initiates from the notch and then transits to a brittle crack during ductile crack propagation. This fracture behavior is termed “inverse fracture.” According to the API Recommended Practice 5L3 (API RP 5L3), a test is considered invalid when a DWTT specimen shows inverse fracture. In this case, it is difficult to examine the acceptance criterion (85% shear area transition temperature) for linepipe steels. Because the purpose of the DWTT is to evaluate the brittle crack arrestability of the steels in a pressurized linepipe, the DWTT results should be examined with a propagating brittle crack arrest test. A large-scale brittle crack arrest test called the West Jefferson test is generally conducted to reproduce the crack propagation and arrest behavior in actual linepipes. However, it is somewhat difficult to control the lower test temperature and to initiate brittle crack in recent high-toughness steels in this burst test. Although the test stress conditions of the uniaxial tension in the plate tension brittle crack arrest test and the biaxial tension in a pressurized pipe are different, the plate tension brittle crack arrest test has the advantages of accurate control of the test temperature, test stress, and brittle crack initiation in comparison with the actual pipe burst test. Therefore, in this study, the brittle crack arrestability of linepipe steel which showed inverse fracture in the DWTT was investigated by conducting plate tension brittle crack arrest tests under an isothermal condition (crack arrest temperature test (CAT test)), which simulates the condition of the actual pipelines in service. This study also investigated the local shear lip thickness fraction in the CAT tests together with the shear area fraction SA% measured in DWTTs. Based on the results, the effect of brittle crack arrestability on inverse fracture appearance in the DWTTs was discussed in comparison with the brittle crack arrest behavior in the CAT tests.

Investigation of damage to thick composite laminates under low-velocity impact and frequency-sweep vibration loading conditions

A detailed investigation of damage and failure mechanisms of composite laminates under low-velocity impact (LVI) by experimental tests and numerical modeling is presented. Five impact energy levels were investigated on composite laminates by drop-weight tests. Permanent indentations were measured, and delamination areas of each interface induced by each LVI event were captured using an ultrasonic C-scan. The 3D volume elements with a user-defined, material-based finite element model (FEM) has been applied to predict the LVI event considering damage modes, including intra-ply damage and inter-ply damage. The results of the FEM were found to agree well with experimental observations. Internal damage of the laminate during the impact process was analyzed. For thick laminates, the initiation of damage is observed at the first layer, and then spreads from the impact surface to the back, leading to a pine-type damage pattern as the thickness increases. Frequency-sweep vibration tests of composite laminates subjected to LVI events were studied under a “fixed ends” boundary condition. Our results show that it is reasonable to use frequency-sweep vibration experiments to evaluate the damage of laminates subjected to LVI events.

Finite element simulation of drop-weight tear test of API X80 at ductile-brittle transition temperatures

This paper proposes a method to simultaneously simulate interacting ductile and cleavage fracture in a DWTT (drop-weight tear test). The stress-modified fracture strain (SMFS) damage model is used to simulate ductile fracture and the maximum principal stress criterion is applied to simulate cleavage fracture. By incorporating the element size effect in the ductile and cleavage damage models, the numerical method to simulate the interacting ductile and cleavage fracture behavior in a DWTT is constructed. To validate the proposed method, the simulation results are compared with six API X80 data measurements at temperatures ranging between -97 °C to -20 °C. The comparison of the experimental load-displacement curve and fracture surface with the FE simulation results shows good agreement.

The effect of temperature-induced phase transition of PTFE on the dynamic mechanical behavior and impact-induced initiation characteristics of Al/PTFE

PTFE is a semi-crystalline polymer which can undergo two phase transitions at 19°Ϲ and 30°Ϲ. To investigate influence of temperature-induced phase transition of PTFE on the mechanical behavior and impact-induced initiation characteristics of Al/PTFE, the dynamic mechanical analysis, split Hopkinson pressure bar test and drop-weight test were conducted at different temperatures. The correlation between fracture modes and ignition mechanism were analyzed associated with microstructures and reaction phenomena. The results show that with the temperature elevated, the mechanical behavior and reactive characteristics of Al/PTFE manifested a bilinear temperature dependence. Al/PTFE went through a gradual transition from brittleness to ductility. The ignition energy declined, explosion flare enhanced and reaction time prolonged consistent with the change of mechanical properties. The shock pressure and ignition time under drop-weight tests were far from the requirement of shock-induced reaction, indicating that it is fracture-induced reaction dominates the ignition of Al/PTFE at low strain rate.

A stochastic particle replacement strategy for simulating breakage in DEM

Description of particle breakage embedded in a simulation using the discrete element method (DEM) qualifies it to describe processes in which breakage is either desired or undesired. DEM codes evolved significantly in recent years, many of which describing breakage. In spite of their limitations representing real particles, spheres have several important advantages from the standpoint of computation efficiency, being the basis for several particle replacement schemes. However, one of its biggest disadvantages lies in the fact that size distributions that are generated are very jagged and unnatural. The work describes a stochastic approach to generate realistic size distributions from breakage of spheres. Families of fragment size distributions were obtained from testing various materials in a drop weight tester. The model also incorporates the description of the unresolved fines. Its application to individual particles demonstrates that the method captures properly the effect of stressing energy described in the analytical model.

A REVIEW BENDING BULKLING AND FLEXURAL VIBRATIONAL ON FIBER METAL LAMINATES FOR AUTOMOBILE SECTOR

In this commitment, the effect dynamic reaction and disappointment methods of fibre–metal overlaid boards exposed to low speed sway were explored and introduced. The fibre–metal cover in this paper involved a layer of glass fibre-fortified plastics sandwiched between two layers of aluminium combination. Two distinct kinds of glass fibre-fortified plastics were utilized for the manufacture: unidirectional and woven. A genuinely broad exploratory examination was directed related to an itemized limited component examination. The examinations were led utilizing a standard drop-weight test machine and the limited component examination was done utilizing a monetarily accessible limited component programming. The aftereffects of greatest contact power, contact span and relating disappointment modes are displayed, looked at and examined in this specialized paper. Scaling impacts in the low speed sway reaction of a polypropylene based fibre metal cover (FML) structure have been examined. To choose aluminium sheet so as to with have properties like erosion obstruction, high effect and weariness quality, great toughness and dependability. To choose great holding glue for FML to defeat delaminating. The aluminium sheet is commonly treated with CH3)2CO with degreasing of material debasements.

The behaviour of thermoplastic and thermoset carbon fibre composites subjected to low-velocity and high-velocity impact

The present paper describes the results from experimental and theoretical modelling studies on the behaviour of continuous carbon fibre/polymer matrix composites subjected to a relatively low-velocity or high-velocity impact, using a rigid, metallic impactor. Drop-weight and gas-gun tests are employed to conduct the low-velocity and high-velocity impact experiments, respectively. The carbon fibre composites are based upon a thermoplastic poly(ether–ether ketone) matrix (termed CF/PEEK) or a thermoset toughened epoxy matrix (termed CF/Epoxy), which has the same fibre architecture of a cross-ply [03/903]2s lay-up. The studies clearly reveal that the CF/PEEK composites exhibit the better impact performance. Also, at the same impact energy of 10.5 ± 0.3 J, the relatively high-velocity test at 54.4 ± 1.0 m s−1 leads to more damage in both types of composite than observed from the low-velocity test where the impactor struck the composites at 2.56 m s−1. The computationally efficient, two-dimensional, elastic, finite element model that has been developed is generally successful in capturing the essential details of the impact test and the impact damage in the composites, and has been used to predict the loading response of the composites under impact loading.

Effect of Accelerated Cooling Rate and Finish Rolling Temperature on the Occurrence of Arrowhead Markings in Drop-Weight Tear Test of API 5LX70 Linepipe Nb–V–Ti Steel Plate

Four Nb–V–Ti steel plates of API 5LX70 linepipe were produced with changing accelerated cooling rate and finish rolling temperature using thermomechanical controlled process. The changes in ductile fracture surface, brittle fracture surfaces, including initial cleavage fracture and inverse fracture, arrowhead marking surfaces, and delamination were investigated using drop-weight tear test at temperatures of 0 °C and − 10 °C. Based on the drop-weight tear test results, an increase in the accelerated cooling rate, resulting in an increase in the volume fraction of quasi polygonal ferrite, fine polygonal ferrite, and granular ferrite microstructures, increased the percentage of ductile fracture surface and decreased the percentage of brittle fracture surfaces. Moreover, a reduction in the finish rolling temperature led to similar changes in the ductile fracture surface and brittle fracture surfaces due to an increase in the volume fraction of aciculae ferrite. Arrowhead markings surfaces, caused by the presence of banded structures, their percentage was reduced by increasing the accelerated cooling rate and decreasing the finish rolling temperature at the temperature of 0 °C. Furthermore, as the accelerated cooling rate increased, the number, length, thickness, and depth of delaminations were reduced at temperatures of 0 °C and − 10 °C.

Experimental study on crumb rubberised concrete (CRC) and reinforced CRC slabs under static and impact loads

ABSTRACT This paper addresses the structural performance of crumb rubberised concrete (CRC) and reinforced CRC slabs under static and low-velocity impact loads. An innovated setup was designed to investigate the impact of behaviour of concrete material based on the drop-weight test. The drop-weight velocities before and after impact were recorded through a laser system. Based on the velocity variation, the energy that was absorbed in concrete material during the test, which also was the impact resistance of the sample’s failure section, had been calculated. CRC samples with rubber percentages varying from 0% to 20% were tested. Experimental results verified the advantages of using rubber on material impact behaviour. Finally, as a structural application, reinforced CRC slabs were tested under static and impact loads. Experimental results showed that CRC slabs exhibited superior post-cracking performance with member moment capacities comparable or even higher than that of reinforced traditional concrete (TC) slabs. It is believed that this unique phenomenon was due to zip-shaped cracking section along CRC slab width. At last, a series of impact tests were conducted and test results showed a significant reduction in the peak stress response in CRC slabs when compared with TC slabs.

Factors influencing impact force profile and measurement accuracy in drop weight impact tests

Drop weight tests on RC beams have been intensively reported in literature. Load cells are commonly used to measure the impact force acting on the beam. Different researchers adopted different configurations, e.g., location of load cells in the test, which could affect the impact load measurement. Although various impact force profiles have been reported by different researchers, there is no systematic study regarding the influences of the test setup on the measured impact forces. Therefore, this study numerically investigates the influences of test setups on impact force measurement accuracy and impact force profile of RC beam under drop weight impact. It is found that when the load cell is embedded into drop weight, the mass distribution of drop weight causes the measured impact force to deviate from the actual contact force acting on the beam. To obtain the true impact force recorded by the load cell mounted at the rear of drop weight head, the drop weight mass ratio αd (i.e., mass of the drop-weight to mass of the head) should be lower than 20. Placing load cell between drop weight and beam changes the local contact stiffness of impact zone and thus leads to different impact force profiles. In addition, the drop weight to beam mass ratio within the range of 0.5 and 4.0 affects the relative velocity between drop weight and beam after the first impulse and hence results in different impact force profiles.

Parameters affecting the behaviour of steel pipes under impact loading

Subsea steel pipes are often used to form extensive networks for transporting oil and gas over large distances. Such pipes can be subjected to actions characterised by high loading rates and intensities stemming from high-mass low-velocity collisions. To ensure that such networks continue to operate, even after being subjected to impact loads, it is essential that the behaviour of the pipes is characterised by a certain level of resilience. Considering that most of the available data obtained from drop-weight tests on steel pipe specimens does not provide a detailed description of the behaviour exhibited throughout the loading process, the work herein aims at investigating numerically, via dynamic nonlinear finite element analysis, the problem at hand. After validating the predictions obtained against the available test data, the numerical investigation focuses on studying the effect of a range of parameters on the exhibited behaviour. The latter parameters are associated with the shape and mass of the impacting object, the geometry and the support conditions of the pipe, the level of axial loading (applied along the axis of the pipe) as well as the level of internal and/or external pressures imposed onto the pipe walls. The numerical predictions reveal that the above parameters, most of which are associated with the in-situ conditions imposed onto subsea pipes throughout their operational life, can influence, potentially detrimentally, the exhibited behaviour. The numerical predictions obtained reveal that this effect is not accurately captured by the existing assessment methods employed in practice for predicting the level of damage suffered by pipes during impact.

Fast ductile fracture: Effect of inertia on propagation resistance and CTOA in pipe steels

In this paper, the effect of inertia on the steady-state velocity of propagating cracks in modern high toughness pipeline steel was investigated. The steel grades examined in this work were American Petroleum Institute Standard X70 and X100. A tensile plate model, simplified from the geometry of a pipe, was studied using the finite element code ABAQUS 6.14–2. The cohesive zone model (CZM) was used to simulate crack propagation. The CZM parameters were calibrated based on matching the crack tip opening angle (CTOA) measured from a drop-weight tear test (DWTT) finite element model to the experimental CTOA of the material. The CZM parameters were then applied to the tensile plate model. The effect of inertia on the steady-state crack velocity was systematically assessed by altering the density of the material used with the plate model. To isolate the influence of inertia, the effect of strain rate on the fracture process and material hardening was neglected and the CZM parameters were assumed constant. It was found that the steady-state crack velocity decreased with increasing mass density; this is consistent with the effect of backfill in pipeline burst tests. The CTOA extracted from the FE model was not affected by the density.

The extended drop weight testing approach – What it reveals

The heterogeneous nature of orebodies introduces large uncertainties into all quantitative evaluations, process design and process predictions. Measuring the extent of the variability of ore competence will allow the design process to account for variation in process performance through a quantitative knowledge of its uncertainties related to ore hardness.The conventional JKMRC drop-weight test (JKDWT) establishes the relationship between input energy (Ecs) and product fineness (t10) from which the breakage potential parameter A × b can be estimated, by combining the broken progeny of groups of particles. A new method, the Extended Drop Weight Test (ExDWT), has been developed which is applied to individual particles and is therefore capable of capturing breakage heterogeneity at high resolution. This paper explores a number of features of the new method, based on breakage tests on individual particles from several different rock types.The results showed that more accurate descriptions of particle size resulted in higher (softer) A × b values which suggests that the standard method may have been over-estimating rock competence. Regular-shaped cores broken diametrally were found to have higher (softer) A × b values than axially broken cores and irregular shaped particles. These tests also suggested that the true ore intrinsic heterogeneity is the main source of breakage variability measured by the ExDWT. The mean A × b values determined by the ExDWT showed no statistical difference to those determined by the standard JKDWT method, but the standard deviation of the estimate was much lower.The results have demonstrated the potential of the new method for capturing the inherent heterogeneity of individual ore particles. Such information could be used to populate multi-component models of comminution.