Impact Test Method 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.

Comparison of post-impact residual strength ratio between hybrid filament-wound cylinder and hybrid plate specimen

The filament-wound (FW) cylinders possess numerous benefits as a high-pressure storage device but are susceptible to impact loads. The presence of post-impact residual strength in an operating FW cylinder has the potential to accelerate the onset of failure. Ensuring the structural integrity and safety of the equipment requires thorough impact testing, which can be expensive and time-consuming, resulting in limited use. This article presents an innovative and cost-effective approach for conducting low-velocity impact testing on a hybrid Al/CFRP filament-wound cylinder by utilizing a simple hybrid Al/CFRP plate specimen. The main focus is to conduct low-velocity impact testing on both types of specimens, followed by post-damage testing that includes tensile tests on the hybrid plate specimen and burst tests on the FW cylinder. The results of laboratory experiments were compared to explicit and implicit numerical models conducted in a broad spectrum of impact energy range and found to be consistent. Using a parameter known as the post-impact residual strength ratio, it is possible to determine the expected impact loading conditions on the hybrid plate specimen that are equivalent to those experienced by the FW-cylinder. This low-cost impact testing method offers a practical and feasible solution to ensure the dependability and safety of FW cylinders throughout their operational lifespan.

Revealing the mechanism of crack initiation and propagation in CGHAZ of S690QL welded joints through low-temperature impact tests with gradient setting of pendulum angle

As the most brittle areas of welded S690QL high-strength steel structures, coarse-grained heat-affected zone (CGHAZ) was crucial for the structural integrity of components. This paper designed an innovative low-temperature impact testing method with a gradient setting of pendulum angle to investigate the micro-mechanism of crack initiation and propagation in the CGHAZ of S690QL welded joints. The results reveal that continuous blocky M−A constituents were distributed along prior austenite grain boundaries (PAGBs), leading to stress concentration and crack initiation. During low-temperature impact processes, cracks propagate in a transgranular mode along {100} or {110} crystal planes. Due to the interaction between compressive stress and the crack tip, regions with high kernel average misorientation (KAM) such as PAGBs can divert the crack. The coarsening of prior austenite grains in the CGHAZ leads to a diminished hindering effect of PAGBs on crack propagation. The findings elucidate the complex relationship between microstructure and impact toughness of CGHAZ, providing insights into crack behavior and mechanisms in CGHAZ.

Influence of post-welding heat treatment on microstructure and peculiarity of 10Cr9Mo1VNb boiler steel welded by hot wire TIG

Hot wire tungsten noble gas (HW-TIG) soldering tests are conducted on 10Cr9Mo1VNb boiler steel with multi-layer and multi-pass, and the soldered joints are subjected to post-weld heat treatment (PWHT) at different temperatures and times from 740°C to 790°C and 1 hour to 4 hours. The influence of PWHT on the microstructure and peculiarity of the joints are analyzed by using hardness, metallography, room temperature tensile testing, Charpy impact testing, SEM, and other experimental methods. The results show that the PWHT can transform the martensite formed in the welding process into tempered martensite, which can significantly improve the uniformity of the microstructure and peculiarity of each area of the joint. When subjected to heat treatment at 740°C, both strength and ductility improve with the increase of heat treatment time, while the plasticity gets a slight decrease. However, when subjected to heat treatment at 790°C, strength, plasticity, and ductility decrease with the increase of time, mainly due to the carbide coarsening such as M23C6 in the joint.

Research on the equivalent impact test method for different pulse widths based on micro-electro-mechanical system devices

The impact pulse width generated by kinetic weapons during launch differs significantly from that produced by conventional laboratory overload impact methods. Consequently, there is an urgent need to develop a method for evaluating the equivalent impact between overload environments characterized by different pulse widths. In the Hopkinson Bar overload test environment, this study presents a method for performing equivalent impact tests based on the Sum of Effective Impact Energy for micro-electromechanical system acceleration sensors, in accordance with the impact dynamics theory and the law of energy variation. It establishes an equivalent impact model for inertial loads with different pulse widths. The dynamic response of the accelerometer to various impact loads was evaluated through the Hopkinson Bar overload test and live firing test, with an error margin of less than 10 %. Timely guidance can be provided for selecting overload parameters in dynamic impact testing, thereby advancing the engineering process of simulating extreme overload environments.

Randomised nano-/micro- impact testing – A novel experimental test method to simulate erosive damage caused by solid particle impacts

A novel randomised nano-/micro-scale impact test method has been developed to experimentally simulate particulate erosion where statistically distributed impacts with defined energy occur sequentially within the test area. Tests have been performed on two brittle glasses (fused silica and BK7) to easily highlight the interaction between impacts, as well as on two ceramic thermal barrier coating systems (TBCs, yttria stabilised zirconia, 7YSZ, and gadolinium zirconate, GZO) that experience erosion in service. Differences in erosion resistance were reproduced in the randomised impact tests, with GZO less impact resistant than 7YSZ, and BK7 significantly worse than fused silica. The impact data show that erosion resistance is influenced by different factors for the glasses (crack morphology, longer-length interaction of radial-lateral cracks in BK7 vs cone-cracking in fused silica) and TBCs (fracture toughness).

Study on bullet impact performance of the HATO-based explosives

In order to study the vulnerability of 1,1'-dihydroxy-5,5'-bistetrazole dihydroxylamine salt (HATO) based explosives, a comparative study of the bullet impact vulnerable characteristics of HATO-based explosives and HMX-based explosives were carried out by using the 12.7 mm bullet impact test method of the 700-group of the Military Mixed Explosives Formulation and Performance Test Methods. The results of the study indicate that due to the friction and impact sensitivities of the HATO and the HMX explosives are similar, and the bullet impact response degree and the safety performance of the HATO-based explosives and HMX-based explosives is equivalent too.

Development and evaluation of the sandwich flexure after impact test

A four-point flexure after impact test method has been developed to assess the damage tolerance of sandwich structures under flexural loading. This test method, recently standardized as standard practice ASTM D8388 by ASTM International, is designed for use with sandwich specimens that have been impact damaged per ASTM D7766. The test method utilizes a four-point flexure fixture to test specimens using the methodology from ASTM D7249, along with modifications specified in the practice. The sandwich configurations investigated consisted of carbon/epoxy facesheets with a Nomex® honeycomb core. Mechanical testing was conducted to evaluate the proposed specimen design, fixturing, and test procedure. Finite element analysis was used to finalize the specimen sizing.

Quantitative analysis of the protective performance of bicycle helmet with multi-direction impact protection system in oblique impact tests

PurposeThe current study aimed to assess the protective performance of helmets equipped with multi-directional impact protection system (MIPS) under various oblique impact loads. MethodsInitially, a finite element model of a bicycle helmet with MIPS was developed based on the scanned geometric parameters of an actual bicycle helmet. Subsequently, the validity of model was confirmed using the KASK WG11 oblique impact test method. Three different impact angles (30°, 45°, and 60°) and 2 varying impact speeds (5 m/s and 8 m/s) were employed in oblique tests to evaluate protective performance of MIPS in helmets, focusing on injury assessment parameters such as peak linear acceleration (PLA) and peak angular acceleration (PAA) of the head. ResultsThe results demonstrated that in all impact simulations, both assessment parameters were lower during impact for helmets equipped with MIPS compared to those without. The PAA was consistently lower in the MIPS helmet group, whereas the difference in PLA was not significant in the no-MIPS helmet group. For instance, at an impact velocity of 8 m/s and a 30° inclined anvil, the MIPS helmet group exhibited a PAA of 3225 rad/s2 and a PLA of 281 g. In contrast, the no-MIPS helmet group displayed a PAA of 8243 rad/s2 and a PLA of 292 g. Generally, both PAA and PLA parameters decreased with the increase of anvil angles. At a 60° anvil angles, PAA and PLA values were 664 rad/s2 and 20.7 g, respectively, reaching their minimum. ConclusionThe findings indicated that helmets incorporating MIPS offer enhanced protection against various oblique impact loads. When assessing helmets for oblique impacts, the utilization of larger angle anvils and rear impacts might not adequately evaluate protective performance during an impact event. These findings will guide advancements in helmet design and the refinement of oblique impact test protocols.

Test Setup for Investigating the Impact Behavior of Biaxially Prestressed Composite Laminates

Instrumented impact testing and compression-after-impact testing are important to adequately qualify material behavior and safely design composite structures. However, the stresses to which fiber-reinforced plastic components are typically subjected in practice are not considered in the impact test methods recommended in guidelines or standards. In this paper, a test setup for investigating the impact behavior of composite specimens under plane uniaxial and biaxial preloading is presented. For this purpose, a special test setup consisting of a biaxial testing machine and a specially designed drop-weight tower was developed. The design decisions were derived from existing guidelines and standards with the aim of inducing barely visible impact damage in laminated carbon fiber-reinforced plastic specimens. Several measurement systems have been integrated into the setup to allow comprehensive observation of the impact event and specimen behavior. A feasibility test was performed with biaxially prestressed carbon fiber-reinforced plastic specimens in comparison with unstressed reference tests. The compressive-tensile prestressing resulted in lower maximum contact forces, higher maximum deflections, higher residual deflections and a different damage pattern, which was investigated by light microscopic analysis. Finally, the functionality of the experimental setup is discussed, and the results seem to indicate that the test setup and parameters were properly chosen to investigate the effect of prestresses on the impacts behavior of composite structures, in particular for barely visible subsequent damages.

Effect of Dry Cupping on Physical Symptom of Headache in Premenstrual Syndrome among Females within 18-26 years : A Randomised Clinical Trial

BACKGROUND: Premenstrual syndrome or PMS are a group of psycho neuroendocrine condition whose cause is not known often experienced prior to menstruation. PMS symptoms are varied with prevalence of premenstrual headache of nearly 43%. Numerous evidences for management of PMS in general are available however literature on specific management of premenstrual headache is unavailable. OBJECTIVE: To determine the effect of dry cupping on physical symptom of headache in the premenstrual syndrome using Daily Record of Severity of Problems (DRSP), Headache Impact test (HIT-6) and Visual Analogue Scale (VAS) METHODS: Females within 18-26 years who complained of premenstrual headache and were willing to participate were included. Subjects were recruited and randomly divided into two groups. Outcome measures used were Daily Record of Severity of Problems (DRSP) and Headache Impact test (HIT-6). Visual Analogue Scale (VAS) was used pre and post intervention. Group A was given cervical traction whereas group B was given dry cupping and cervical traction. DRSP and HIT-6 were recorded for four cycles. RESULTS: The mean of demographic data suggested that both the group were homogenous at the baseline in terms of age and BMI. HIT-6 mean scores when compared from baseline to 2nd follow up for both the groups demonstrated statistically significant outcome. This improvement was maintained for over a period f two cycles in group B. DRSP and VAS mean scores were compared from baseline to post intervention showed high statistically significant improvement (p=0.0001) CONCLUSION: The study concludes that dry cupping is an effective tool for immediate to long term reduction of premenstrual headache symptoms.

Development and evaluation of the sandwich edgewise compression after impact test

A compression after impact test method has been developed to assess the damage tolerance of sandwich structures under edgewise compressive loading. This test method, recently standardized as ASTM D8287, was designed to test specimens that have been impact damaged per ASTM D7766. The fixture design utilizes end loading with top and bottom edge supports to prevent end-brooming and out-of-plane rotation. Additionally, knife edge side supports provide out-of-plane restraint to buckling, similar to the existing laminate edgewise compression after impact test fixture. The sandwich configurations investigated were constructed from glass/epoxy and carbon/epoxy facesheets with a Nomex honeycomb core. Mechanical testing was conducted to evaluate the proposed specimen design, fixturing, and test procedure. Finite element analysis was used to verify the strain gage placement and damage size limits.

An experimental and numerical study on the hybrid effect of basalt fiber and polypropylene fiber on the impact toughness of fiber reinforced concrete

As the civil aviation industry advances, higher requirements are put forward for the performance of airport cement pavement. The frequent takeoffs and landing of aircraft will cause continuous and large impact load on airport pavement, and combined with long-term natural factors, there will be various structural diseases. These diseases not only affect the service life of pavement, navigation safety. To enhance the impact resistance and durability of concrete, the incorporation of fiber has proven an effective approach, and basalt fibers (BF) and polypropylene fibers (PF) are selected as reinforcement materials in this study. Firstly, the effects of single BF and hybrid BF and PF on the mechanical properties of concrete were explored through compressive and flexural tests considering fiber volume contents (0.1%, 0.15, 0.2%) and lengths (6 mm, 9 mm, 12 mm). Then, the drop hammer impact test method, recommended by ACI committee 544, was refined to evaluate the impact resistance toughness of concrete. Finally, the numerical simulation of the impact test was established to explain the concrete impact damage mechanism. The results show that under less than 0.15% volume content, the single BF can effectively enhance the compressive strength, flexural strength, and impact resistance of concrete. Compared with the single BF, the combination of 12 mm BF and 6 mm PF yields favorable results, encompassing improved mechanical properties and impact resistance, thus exhibiting a positive hybrid effect. The increase in PF length (9 mm) leads to a reduction in compressive strength but an improvement in flexural strength and impact resistance. The simulation of the impact test is constructed and the accuracy is confirmed by comparing the impact times and failure patterns of the specimens. The tensile damage of plain concrete is much greater than the compressive damage, and the cracks will spread rapidly from the upper surface to the lower surface. Compared with plain concrete, the crack width of hybrid fiber reinforced concrete is larger, but the damage degree is more uniform. Fiber can absorb a large amount of impact energy, reduce the emergence of micro-cracks, and improve the impact toughness and toughness coefficient of concrete.

BRAKE SURFACE TEXTURE EXPLORATION AND TEMPERATURE CONTROL DURING BRAKING IN THE NEW KNEE IMPACT TEST

During the braking process, frictional heat generation between brake strip and brake block can lead to high temperatures, significantly affecting the braking performance. This paper proposes a novel knee impact test method and innovatively investigates the effect of brake friction surface texture shape on braking performance. A comparative evaluation of the braking performance of different surface textures is conducted using the new knee impact test, with a focus on studying the temperature rise during braking to optimize the brake system. Research findings indicate that the best braking performance was achieved when friction surface texture of the brake block was rhombus-shaped with a diagonal ratio of 5:5. By implementing this improved brake design, the maximum temperature during braking was reduced from 184.44[Formula: see text]C to 75.963[Formula: see text]C, resulting in a significant reduction in thermal stress from 155.22 MPa to 64.40 MPa. Moreover, the acceleration and brake distance are extracted and compared with the target values of Euro NCAP. The improved brake acceleration exhibits stability and a deviation from target value within 10%. Additionally, the deviation between our brake distance and target distance is −3.63%. These results provide a valuable reference for improving the braking performance of braking systems in the new knee impact test.

Assessment of Different Approaches for Measuring Shear Fracture Appearance in Charpy Tests

Abstract Different approaches for establishing shear fracture appearance (SFA) on tested Charpy specimens were assessed and compared, namely (in order of increasing expected accuracy) estimates based on characteristic forces from instrumented Charpy tests, optical measurements using image analysis software, and measurements performed with the aid of a scanning electron microscope. Comparisons between different SFA values for 129 instrumented Charpy tests currently included in the National Institute of Standards and Technology database allowed us to establish the relationships between the different available approaches and formulate recommendations for the revision of the standards ASTM E2298-18, Standard Test Method for Instrumented Impact Testing of Metallic Materials, and ISO 14556:2015, Metallic Materials — Charpy V-Notch Pendulum Impact Test — Instrumented Test Method, which currently provide four empirical correlations that can be used to estimate SFA.

Repeated impact behavior of preplaced aggregate concrete incorporating different fiber types

This research used an experimental approach to examine the impact performance of preplaced fibrous aggregate concrete with various fibre types. Four concrete mixtures were produced with identical quantities except for the type of fiber. The first reference mixture was plain, while the other mixtures were reinforced with 2.5% of polypropylene fibers (PP), short steel fibers (SF1) and long steel fibers (SF2). In accordance with the ACI 544-2R impact test method, six cylindrical discswere tested from each mixture using drop-weight impact loading. The tests' results revealed that adding fibre, irrespective of the type of fiber used, considerably enhanced the impact strength at the cracking (Ncr) and failure (Nf) phases. Compared to their plain concrete specimens, fibrous specimens showed increased Ncr ranging from 395 to 655% and Nf from 727 to 1973%. Steel fibers exhibited higher impact strength by 33 to 151% and higher ductility by 44 to 64% compared to PP fibers. Besides, a longer steel fiber performed better under impact loads than shorter steel fibers, where Ncr and Nf were higher by 14 and 31%, respectively.

Human Head and Helmet Interface Friction Coefficients with Biological Sex and Hair Property Comparisons.

Dummy headforms used for impact testing have changed little over the years, and frictional characteristics are thought not to represent the human head accurately. The frictional interface between the helmet and head is an essential factor affecting impact response. However, few studies have evaluated the coefficient of friction (COF) between the human head and helmet surface. This study's objectives were to quantify the human head's static and dynamic COF and evaluate the effect of biological sex and hair properties. Seventy-four participants slid their heads along a piece of helmet foam backed by a fixed load cell at varying normal force levels. As normal force increased, static and dynamic human head COF decreased following power-law curves. At 80 N, the static COF is 0.32 (95% CI 0.30-0.34), and the dynamic friction coefficient is 0.27 (95% CI 0.26-0.28). Biological sex and hair properties were determined not to affect human head COF. The COFs between the head and helmet surface should be used to develop more biofidelic head impact testing methods, define boundary conditions for computer simulations, and aid decision-making for helmet designs.

Evaluation of full-face, open-face, and airbag-equipped helmets for facial impact protection

ObjectiveTwo-wheeler riders frequently sustain injuries to the head and face in real-world crashes, including traumatic brain injury, basilar skull fracture, and facial fracture. Different types of helmets exist today, which are recognized as preventing head injuries in general; however, their efficacy and limitations in facial impact protection are underexplored. Biofidelic surrogate test devices and assessment criteria are lacking in current helmet standards. This study addresses these gaps by applying a new, more biofidelic test method to evaluate conventional full-face helmets and a novel airbag-equipped helmet design. Ultimately, this study aims to contribute to better helmet design and testing standards. MethodsFacial impact tests at two locations, mid-face and lower face, were conducted with a complete THOR dummy. Forces applied to the face and at the junction of the head and neck were measured. Brain strain was predicted by a finite element head model taking both linear and rotational head kinematics as input. Four helmet types were evaluated: full-face motorcycle and bike helmets, a novel design called a face airbag (an inflatable structure integrated into an open-face motorcycle helmet), and an open-face motorcycle helmet. The unpaired, two-sided student’s t-test was performed between the open-face helmet and the others, which featured face-protective designs. ResultsA substantial reduction in brain strain and facial forces was found with the full-face motorcycle helmet and face airbag. Upper neck tensile forces increased slightly with both full-face motorcycle (14.4%, p >.05) and bike helmets (21.7%, p =.039). The full-face bike helmet reduced the brain strain and facial forces for lower-face impacts, but not for mid-face impacts. The motorcycle helmet reduced mid-face impact forces while slightly increasing forces in the lower face. Significance of resultsThe chin guards of full-face helmets and the face airbag protect by reducing facial load and brain strain for lower face impact; however, the full-face helmets’ influence on neck tension and increased risk for basilar skull fracture need further investigation. The motorcycle helmet’s visor re-directed mid-face impact forces to the forehead and lower face via the helmet’s upper rim and chin guard: a thus-far undescribed protective mechanism. Given the significance of the visor for facial protection, an impact test procedure should be included in helmet standards, and the use of helmet visors promoted. A simplified, yet biofidelic, facial impact test method should be included in future helmet standards to ensure a minimum level of protection performance.

Crashworthiness of the bollard system by experimentally validated virtual test

Shielding risky/vulnerable roadside zones in urban areas such as playgrounds, sidewalks, bus stations, oil/gas stations, and regulators of infrastructure facilities has been a significant focus point by engineers and local authorities in recent decades due to the boost of vehicular number and mobility. Bollard systems are regarded as one of the efficient countermeasures, especially for the zones that vehicles and pedestrians share. This paper discusses the performance of a steel bollard system by experimentally validated virtual crash tests following IWA 14-1 (Vehicle security barriers (VSB): Performance requirement, vehicle impact test method and performance rating), EN 1317 (Road Restraint Systems), and EN 16303 (Validation and verification process for virtual testing in crash testing against vehicle restraint system) standards. In this context, pendulum crash tests were performed, virtual pendulum crash tests were verified and modelled with the results of actual tests then full-scale virtual crashworthiness tests were conducted respectively. The penetration, Acceleration Severity Index (ASI), displacement, and deformation values of the bollard system were evaluated considering the relevant standards and the characteristics of urban traffic. Based on virtual test results with increased reliability, the bollard system has the capability to shield the roadside critical assets against M1 class 900 kg vehicles up to 50 km/h and M1 class 1500 kg vehicles up to 32 km/h.

Effect of one-year corrosion on steel bridge materials in the maintenance stage with the Charpy impact test method

Corrosion of steel bridges is a major problem because it has the potential to reduce the performance of the structure over its lifetime. One factor that should not be reduced is fracture toughness, so this should be a very important concern in the maintenance program. Existing guidelines do not specify when corrosion conditions are hazardous and when corrosion conditions are not hazardous to structural performance. This study aims to explain how long corrosion does not cause danger, and when corrosion becomes dangerous. The Charpy Impact Test was used in this study to examine the effect of corrosion with a corrosion duration of weekly up to one year on fracture toughness. The series of tests in this research program used SM-490-type specimens which are steel plates commonly used for bridge structures. Specimens with variations in corrosion duration which were the result of immersion in sulfuric acid solution to simulate corrosion growth were then subjected to crack toughness testing. The toughness of each specimen was tested with a corrosion period starting from 1 week and so on up to 1 year to determine the level of fracture toughness. The results obtained from all tests showed that there was no decrease in the toughness of the corroded specimens for up to 1 year. The data presented in this study is very helpful for the designers and maintainers to plan corrosion treatment programs with clearer and more accurate considerations in assessing the structural integrity of steel bridges affected by corrosion.