Instrumented Impact Machine Research Articles

Effects of lubrication in high speed falling dart testing of elastomer materials

The effect of lubrication in falling dart testing of elastomer materials has been studied experimentally. The test results for two different vulcanisate types (NBR/SBR and EPDM) at velocities of 5, 10, 20 and 30 m/s, with and without lubrication of the impactor (tup), are presented. Various types of lubricant were used in order to explore their influence on the test results for the elastomer samples. The measurements were conducted exclusively with a high speed falling dart instrumented impact machine. The results show that lubrication is a significant factor in falling dart tests bur the type of lubricant itself has no relevant influence on the test results.

Impactor Mass Effects in Glass–Epoxy Composites Subjected to Repeated Drop Tests

Experimental studies were carried out to understand the impactor mass effects on glass–epoxy composites using an instrumented impact machine (DYNATUP 8250) under low-velocity test conditions. Repeated drop tests were carried out at pre-determined energy levels for selective mass height combinations. Number of drops to failure (Nf) was chosen as the damage criterion. Analysis of test results clearly showed that, at low incident energies, heavier impactors caused more damage to the laminates as reflected by their lower number of drops to failure. This effect diminished gradually at relatively higher incident energies.

Dynamic fracture characteristics of the osteochondral junction undergoing shear deformation

This paper presents a biomechanical study of the dynamic fracture response of the osteochondral regions of both immature and mature cartilage-bone laminates induced through shear loading. An instrumented impact machine, providing both mechanical and real-time macro-photographic fracture data, was used to load the osteochondral region in shear by means of a direct compressive force applied to the cartilage layer only, and in a direction parallel to the plane of the osteochondral junction. This force was applied at a known velocity of 2500 mm/s. Our results show that under these conditions of shear loading the dynamic mode II fracture toughness of the osteochondral region of the mature tissue is approximately 1.5 times that of its immature counterpart, and that the derived dynamic shear stiffness of the immature tissue is about 4 times that of the mature. The structural studies demonstrated that the mature tissue delaminates within a well-defined tidemark region whilst the immature fractures through the subchondral bone into which fingers of articular cartilage penetrate. We suggest that this pseudo-brittleness of the immature tissue could explain why there is an increased susceptibility to osteochondral failure in the younger human joint. Finally, we note that the strength-to-toughness relationship, in which stiffer engineering materials are known to exhibit lower fracture toughness, also applies to the cartilage-bone system.

Uniaxial tensile response of microfibre reinforced cement composites

Microfibre reinforced cement composites reinforced with high volume fractions of carbon, steel and polypropylene fibres were tested in uniaxial tension. Composites investigated included those with only one type of fibre (mono-fibre composites) and those with two or more types of fibres (hybrid-fibre composites) in the same mix. Considerable strengthening, toughening and stiffening of the host matrix due to microfibre reinforcement were observed. In the hybrid-fibre composites, different fibres appear to act as additive phases; i.e., they maintain their individual reinforcing capabilities. The composites were also impact tested in uniaxial tension using a newly designed instrumented impact machine. When compared with static test results, considerable sensitivity to stress rate was noted; composites were found to be stronger and tougher under impact and the improvements were more pronounced at higher fibre volume fractions. The potential of these composites for use in thin sheet products and other similar applications is recognized, and the need for continued research is stressed.

Micro-fiber reinforced cement composites. I. Uniaxial tensile response

Stress–strain curves in uniaxial tension were obtained for micro-fiber reinforced cement composites reinforced with high volume fractions of carbon, steel, and polypropylene fibers both in the mono and hybrid (combination) forms. Considerable strengthening, toughening, and stiffening of the host matrix due to micro-fiber reinforcement was observed. In the hybrid fiber composites, different fibers appear to act as additive phases, i.e., they maintain their individual reinforcing capabilities. The composites were also impact tested in uniaxial tension using a newly designed instrumented impact machine. When compared with static test results, considerable sensitivity to stress-rate was noted; composites were found to be stronger and tougher under impact and the improvements were more pronounced at higher fiber volume fractions. The paper recognizes the potential of these composites for use in thin sheet products and other similar applications, and stresses the need for continued research. In Part II of this paper, these composites will be characterized under an applied flexural load and a fracture criterion will be developed through crack growth tests. Key words: fiber reinforced cements, tension, strength, ductility, impact.

Effects of V-Notch Dimensions on Charpy Impact Test Results for Differently Sized Miniature Specimens of Ferritic Steel

In order to develop the small specimen technology in Charpy impact testing, the effects of V-notch dimensions on the test results were investigated for miniaturized specimens of a ferritic steel, Japanese Ferrite/Martensite Dual Phase Steel (JFMS). The miniaturized Charpy specimens had four different square cross-sections of 3.3, 2, 1.5 and 1 mm, and each of them had a variety of V-notch dimensions (notch depth, notch root radius and notch angle). All of the specimens were subjected to Charpy impact tests between 93 and 373 K using a specially instrumented impact machine. The fracture surfaces of all tested specimens were examined by scanning electron microscopy

Critical impact initiation energies for three HTPB propellants

The instrumented drop weight impact machine is one possible candidate for establishing the hazard response of solid rocket propellants to impact. The plastic work done on the propellant prior to initiation can be measured by equating it to the loss in drop weight kinetic energy, provided energy storage in the machine is negligible. Three HTPB/AP propellants were studied with an instrumented impact machine. Data are given for impact velocities ranging from 5.54 m/s, at which no sample was consumed, to 16.14 m/s, at which nearly all of the sample was consumed. These data are interpreted in terms of a proposed mechanism based on other impact tests. On bare steel tools ignition, as opposed to hot spot formation, is assumed to occur at impact velocities greater than 10.3 m/s, when more than 90% of the sample is consumed during the test. At higher impact velocities, for the present data, times to reaction are short and the change in impactor kinetic energy during the initiation delay is defined as the critical initiation energy. Some of the trends in the data are correlated with the propellant formulations. The present test is contrasted with others suggested for impact sensitivity characterization in terms of both initiation threshold and response severity.

A comparison of Charpy and Izod test modes for polystyrene

A number of polystyrenes and rubber-modified polystyrenes were tested in an instrumented impact machine which could be set to either the Charpy or the Izod test configuration. Using simple beam considerations, the stress intensity factor, K c calculated in either test mode was adequate to describe the fracture behaviour. The fracture toughness values were found to be in the range quoted in the literature. This work showed that Charpy and Izod test results may be directly compared independent of fracture mode.

Impact behaviour of concrete beams

An instrumented impact machine was used to carry out impact tests on concrete beams, 100×125 mm in cross-section and 1400 mm long. The simply supported beams were struck at their midpoints by a 345 kg mass impact hammer, dropped from various heights. The instrumentation included strain gauges mounted on the striking end of the hammer, strain gauges mounted on one support anvil, and three accelerometers placed at various locations along the beam. The data were collected using a 5-channel data acquisition system. Normal strength, high strength, and fibre reinforced concrete beams were tested. In general, it was found that the properties of concrete under the high stress rates associated with impact loading could not be predicted from conventional static tests.

The fracture of wood under impact loading

High speed motion picture photography was used to study the fracture, under impact loading, of wood beams. Photographs were taken at the rate of 500 frames per second, which permitted the crack development during the fracture event to be monitored. Load vs. time data during the test were also recorded. This paper presents a photographic record of the crack patterns which developed when the beams were tested in an instrumented impact machine.

Investigations into the influence of the tup velocity and the heat treatment on the Dynamic Fracture Toughness of inconel 625

AbstractExperiments were performed with an instrumented impact machine using different drop heights, on the nickel base alloy Inconel 625 in the as‐received state and after heat treatment for about 3.6 Ms (1000 h) at 923 K (650°C).The absorbed impact energy can be obtained either by the direct dial reading, by the integration of the load versus load point displacement diagram or by the integration of the load versus time diagram, knowing the initial impact velocity v0 of the tup. In all cases the agreement was excellent.It is shown that. the dynamic fracture toughness is dependent on the tup velocity v0 and, as a consequence, on the total energy of the hammer at the different drop heights. defining a dynamic stress σ from the velocity dependence of the fracture toughness, the stress σ is higher for the embrittled material – a tendency verified by tensile tests. the dynamic fracture toughness can be correlated with the absorbed impact energy up to the load maximum for the heat treated material while the as‐received material exhibits no such dependence. The change in the tup velocity during the impact process is only small for this type of material.

Results from investigations with an Instrumented Impact Machine on a molybdenum base alloy, nickel base alloys, and incoloy 800

AbstractExperiments were performed on the molybdenum base alloy TZM, the nickel base alloys Nimocast 713 LC, Inconel 625, Nimonic 86, Hastelloy S, and the iron base alloy Incoloy 800 with an instrumented impact machine. The results are discussed in terms of absorbed impact energies and dynamic fracture toughness.In all cases the agreement between the energy determined by the dial reading and the energy determined by the integration of the load vs. load point displacement diagram was excellent.A procedure for the determination of the dynamic fracture toughness for load vs. load point displacement diagrams exhibiting high oscillations using an averaged curve is proposed. Using this procedure a pronounced influence of the experiments with tup and chisel (5.0 m/s and 0.1 m/s respectively) on the dynamic fracture toughness is not detectable. Using half the drop height, i.e. halving the total energy, lowers the dynamic fracture toughness values for these types of alloys. Low absorbed impact energies are often combined with high fracture toughness values. In these cases there is no or only a small reserve in deformation and/or stable crack growth.

The effect of hydrogen and strain rate on the “ductile-brittle” behaviour of zircaloy

Tests have been made on hydrided and non-hydrided zircaloy Charpy specimens in slow bend and also at impact rates of strain using an instrumented impact machine. The dynamic and static yield stresses have been determined over a wide temperature range and it is concluded that different mechanisms control yielding at the two strain rates. The strain rate sensitivity of the yield stress is accompanied by a strain rate sensitivity of the “ductile-brittle” transition. The energy absorbed by non-hydrided zircaloy specimens is increased by testing at high strain rates, whereas hydrided zircaloy is considerably embrittled by increasing the strain rate.