Chevron Marks Research Articles

Preservation of groove mark striae formed by armoured mud clasts: The role of armour sediment size and bed yield stress

AbstractStriated grooves in tool marks are common at the base of sandstones, especially in deep‐marine successions, but their use in physical‐process and environmental reconstruction is underdeveloped. To fill this gap in knowledge, striations in the central groove of chevron marks and in chevron‐less groove marks were formed in the laboratory by dragging tools armoured with silt, sand or gravel across muddy substrates. These experiments simulated the formation of striated grooves by armoured mud clasts carried at the base of quasi‐laminar and fully laminar debris flows, aiming to: (1) delineate the bed shear strengths for the formation of striated grooves at different armour sediment sizes; (2) examine how the preservation potential of striated grooves depends on clay bed rheology and size of armour sediment and (3) discuss how the pre‐lithification clay bed consolidation state and size of armour sediment can be reconstructed from striated grooves in the geological record. The experimental results revealed that tools with small‐diameter silt and sand armours dragged along soft beds lack striations or, at best, leave poorly defined striations, whereas firm beds and gravel armours exhibit well‐defined striations. The spacing of striations formed by gravel clasts corresponds well with the clast diameter, implying that striation spacing is a good proxy for the diameter of armoured gravel under natural conditions. In contrast, the spacing of striae formed by sand armours is greater than the grain diameter, suggesting that the spacing of fine striations can only be used to predict a maximum armour sand size. A comparison of different processes of formation of armoured mud clasts demonstrated that the armouring of mud clasts most probably happens after incorporation of the clasts by erosion into the head of the debris flow and subsequent movement across a loose sandy or gravelly bed surface.

On the origin of chevron marks and striated grooves, and their use in predicting mud bed rheology

AbstractUnderstanding of the formative conditions of many sole structures is limited, with chevron marks and striated groove marks being particularly enigmatic. These sedimentary structures are examined here through laboratory modelling. An idealized tool, resembling an armoured mud clast, was dragged through substrates of kaolinite–seawater mixtures of different yield strengths while submerged in seawater. The experiments suggest that armoured mud clasts are the likely tools producing fine striae in striated grooves and, given the common occurrence of striated groove marks in outcrops, that these clasts are more prevalent in deep‐marine settings than previously thought. Chevron marks were observed to form over a narrow range of substrate yield stresses, likely explaining their relative rarity. Furthermore, their form is shown to be a function of substrate rheology, with chevron angle relative to the movement direction of the tool being less in weaker substrates. Moreover, the size of cut chevron marks, characterized by a narrow central cut, bears no relationship to the size of the incising tool, but rather reflects a substrate with a low yield stress that is sufficiently mobile to close behind the tool. In contrast, interrupted chevron marks, characterized by a distinct central groove, reflect greater substrate strength. Striated grooves without chevrons formed at the highest yield stresses simulated in the experiments. The relationship between tool mark type and yield stress, in combination with changes in chevron angle, enables these sole structures to be utilized as indicators of palaeosubstrate rheology. The conditions required to preserve such features include a prolonged period of bed consolidation, flow bypass and lack of bioturbation. Given changes in seafloor communities and bioturbation over time and their impact on substrate rheology, particularly during the early Palaeozoic, the present work supports the idea that the frequency of these sole structures likely changed over geological time.

Analysis of a new species of the Astyanax orthodus group (Characiformes: Characidae) from the upper Madre de Dios River, Amazon River Basin, Peru

Based on ten specimens, using morphometric, meristic and osteological characters, Astyanax leoni n. sp. is described from the upper Madre de Dios River drainage, Amazon River Basin of Peru. A. leoni n. sp. is a member of the Astyanax orthodus species group and is distinguished (except from A. multidens, A. villwocki, and A. gandhiae) in having an inconspicuous rod-shaped stripe on the caudal peduncle that extends anteriorly on top of a silver lateral stripe. It differs from the species mentioned above as follows: from A. multidens by having shorter chevron marks that cover up to only two series of scales above and below the apex of the chevron (vs. chevrons taller, with extensions that cover three series of scales); from A. villwocki by having chevron markings along the entire body (vs. no chevrons on the caudal peduncle); It differs from Astyanax gandhiae in having the caudal peduncle spot extending anteriorly to beyond the tip of the dorsal fin (vs. caudal peduncle spot not reaching anteriorly to tip of dorsal fin), and not of a uniform width as in A. villwocki. A dichotomous key to the species of Astyanax orthodus group is included.

Countermeasures to Reduce Truck-Mounted Attenuator (TMA) Crashes: A State-of-the-Art Review

To support worker and driver safety, this study conducted a comprehensive literature review to identify methods of enhancing TMA visibility, improving work zone configurations, and ensuring worker safety. To increase TMA recognition, this study observed that the use of a 6-to-8-inch wide yellow and black inverted ‘V’ pattern of retroreflective chevron markings, sloped at a 45-degree angle downward in both directions from the upper center of a rear panel is effective in alerting drivers to work zones. This study also recommends applying amber and white warning LEDs, which flash in an asynchronous pattern at a 1 Hz frequency and are mounted against a solid-colored background for a 360-degree view visible at least 1500 feet from the work zone. In addition, a work zone vehicle configuration consisting of a lead, buffer, and advance warning truck with a buffer space between 100 and 150 ft is suggested to reduce the risk of lateral intrusions and TMA roll-ahead. In parallel, workers should wear high-visibility vests noticeable at a minimum distance of 1000 feet and headwear with at least 10 square inches of retroreflective material. Some intelligent transport systems are also suggested to enhance TMA recognition and potentially minimize work zone fatalities. Application of the recommended guidelines will potentially improve current practices and significantly reduce the occurrence of TMA crashes in construction and maintenance work zones.

Sedimentary structures associated with hybrid event beds from the Gull Island Formation (Pennsylvanian) of north Clare, Ireland

A previously unreported assemblage of sedimentary structures, including several types of ripple, chevron marks, ridge and furrows, plant-rich laminations, found in association with hybrid event beds, with related muddy debrites and the trace fossil Kouphichnium, is described from a short 10m section through the middle of the Gull Island Formation [GIFm] (Pennsylvanian) of northern County Clare, Ireland. The section exposes a sequence of thickening and coarsening-upwards gravity flow deposits and interbedded mudstone layers. The upper part of the section is dominated by thick, massive and amalgamated sandstone beds; the middle section contains thinner sandstone beds with debritic mudstone caps, while the lowermost section comprises thin beds with a range of sedimentary structures produced by low density, transitional flows influenced by mud content, including mud ripples. 'High-density' turbidity currents operating in a delta front setting are inferred to have transformed to hybrid event beds with dilute but mud-rich suspensions travelling further distally to emplace thin beds, with evidence for clay-induced transitional flow and an assemblage of sedimentary structures not previously described from the GIFm. Small-scale ripple foresets from the upper part of the lower section indicate a southerly component of palaeocurrent flow direction. Chevron marks show size and palaeo-flow direction variation, suggesting temporal changes in current flow. Ridge and furrows have previously been interpreted as being formed under the head of turbidity current; however, the scale of the ridge and furrows described here suggest that interpretation is unlikely and some other unknown mechanism is involved. The presence of Kouphichnium trackways is significant as Carboniferous examples of this ichnofossil are usually recorded from very shallow marine or marginal marine environments. This part of the GIFm in north Clare is interpreted as a shallowing, delta front lobe environment exhibiting an upward transition from marginal or distal lobe to proximal or axial lobe sub-environment. This study highlights the influence of flow transformation in a muddy delta front environment with a high level of sediment supply favouring sediment remobilisation and the generation of a distinctive suite of sedimentary structures.

Sedimentary Structures Associated With Hybrid Event Beds From the Gull Island Formation (Pennsylvanian) Of North Clare, Ireland

A previously unreported assemblage of sedimentary structures, including several types of ripple, chevron marks, ridge and furrows, plant-rich laminations, found in association with hybrid event beds, with related muddy debrites and the trace fossil Kouphichnium, is described from a short 10m section through the middle of the Gull Island Formation [GIFm] (Pennsylvanian) of northern County Clare, Ireland. The section exposes a sequence of thickening and coarsening-upwards gravity flow deposits and interbedded mudstone layers. The upper part of the section is dominated by thick, massive and amalgamated sandstone beds; the middle section contains thinner sandstone beds with debritic mudstone caps, while the lowermost section comprises thin beds with a range of sedimentary structures produced by low density, transitional flows influenced by mud content, including mud ripples. ‘High-density’ turbidity currents operating in a delta front setting are inferred to have transformed to hybrid event beds with dilute but mud-rich suspensions travelling further distally to emplace thin beds, with evidence for clay-induced transitional flow and an assemblage of sedimentary structures not previously described from the GIFm. Smallscale ripple foresets from the upper part of the lower section indicate a southerly component of palaeocurrent flow direction. Chevron marks show size and palaeo-flow direction variation, suggesting temporal changes in current flow. Ridge and furrows have previously been interpreted as being formed under the head of turbidity current; however, the scale of the ridge and furrows described here suggest that interpretation is unlikely and some other unknown mechanism is involved. The presence of Kouphichnium trackways is significant as Carboniferous examples of this ichnofossil are usually recorded from very shallow marine or marginal marine environments. This part of the GIFm in north Clare is interpreted as a shallowing, delta front lobe environment exhibiting an upward transition from marginal or distal lobe to proximal or axial lobe sub-environment. This study highlights the influence of flow transformation in a muddy delta front environment with a high level of sediment supply favouring sediment remobilisation and the generation of a distinctive suite of sedimentary structures.

Investigation of failure mechanism of a DCI engine connecting rod

In reciprocating engines, connecting rod cap and connecting bolts are critical as they are exposed to varying loads under different operating conditions. This paper focused on the failure of the connecting rod of a 1.5 dci K9K diesel engine. As a result of the engine operating for approximately 378400 km, the connecting rod was broken, and the reasons for the failure of the connecting rod cap and connecting bolt were investigated. The connecting rod of the K9K engine was designed in accordance with the dimensions in SolidWorks software and then exported to ANSYS software for stress and fatigue analysis. Also, the macrostructure of the broken connecting rod cap and bolt was investigated. We knew that the mechanic who fixed the engine about two years ago tightened the connecting rod bolts without using a torque meter. Therefore, stress and fatigue analyzes were performed to determine the effect of different tightening torques (ranging from 22.5 to 52.5 Nm) at 2000 rpm. According to the numerical analysis results, with increasing tightening torque, the maximum equivalent stress and alternating stress values increased significantly, while the fatigue safety factor and the cyclic life of the connecting rod decreased. First, a fatigue fracture occurred in the right hand bolt. Immediately after, the lower cup deformed and crashed to the cylinder liner. Therefore, a brittle fracture occurred on the left shoulder of the connecting rod shank. The chevron markings were clearly visible in the macrostructure as evidence of brittle fracture.

An Airport Knowledge-Based Method for Accurate Change Analysis of Airport Runways in VHR Remote Sensing Images

Due to the complexity of airport background and runway structure, the performances of most runway extraction methods are limited. Furthermore, at present, the military fields attach greater importance to semantic changes of some objects in the airport, but few studies have been done on this subject. To address these issues, this paper proposes an accurate runway change analysis method, which comprises two stages: airport runway extraction and runway change analysis. For the former stage, some airport knowledge, such as chevron markings and runway edge markings, are first applied in combination with multiple features of runways to improve the accuracy. In addition, the proposed method can accomplish airport runway extraction automatically. For the latter, semantic information and vector results of runway changes can be obtained simultaneously by comparing bi-temporal runway extraction results. In six test images with about 0.5-m spatial resolution, the average completeness of runway extraction is nearly 100%, and the average quality is nearly 89%. In addition, the final experiment using two sets of bi-temporal very high-resolution (VHR) images of runway changes demonstrated that semantic results obtained by our method are consistent with the real situation and the final accuracy is over 80%. Overall, the airport knowledge, especially chevron markings for runways and runway edge markings, are critical to runway recognition/detection, and multiple features of runways, such as shape and parallel line features, can further improve the completeness and accuracy of runway extraction. Finally, a small step has been taken in the study of runway semantic changes, which cannot be accomplished by change detection alone.

Microstructure and room-temperature mechanical properties of crystalline and amorphous FeAl based melt spun ribbons

The microstructure and mechanical properties of crystalline Fe81%-Al19% and amorphous Fe72%-Al14%-B14% ribbons obtained by the melt spinning technique are studied. A different grain size in each surface of the crystalline ribbon has been found. This is caused by the temperature gradient originated by the manufacturing process. The micro-hardness and the Young's modulus were evaluated by instrumented micro-indentation (P-h curves) and conventional tensile test. The results show different Vicker's hardness on each surface for each of the ribbons, being these values greater in the amorphous ribbon than in the crystalline one. The values of the Young's modulus are 133 ± 11 GPa and 210 ± 20 GPa for the crystalline and amorphous ribbon respectively which are in good agreement with the theoretical values obtained by the mix rule. The surface fracture shows a brittle-like aspect with presence of cleavage in the Fe81%-Al19% ribbon and small localized ductile behavior before reaching the fracture. In the other hand, in the Fe72%-Al14%-B14% ribbon, the surface fracture characteristics reveal a fragile fracture and the presence of chevron marks. There is a concordance between the mechanical behavior and the micro-mechanism responsible for the fracture.

Computer simulation of cleavage fracture surface morphologies in steel plates

A computer simulation model has been developed to reproduce brittle fracture surface morphologies. Local stress intensity factor along a propagating crack front is calculated considering the fracture surface irregularity and crack front non-straightness. Shear stress exerted at fracture surface steps and crack closure stress by uncracked ligament are also taken into consideration in calculating the local stress intensity factor. The local stress intensity factor is compared with assumed critical value to judge if a crack propagate or arrests at each crack front location. The model was found to reproduce chevron markings and shear-lips, both of which are typical of cleavage fracture in steels. The present model was applied to wide-plate crack arrest test with temperature-gradient. Changes of fracture surface morphologies and arrest crack length were well reproduced by the present model.

Failure Analysis on Conveyor Chain Links of a Central Bucket Elevator

Failure of chain links of a bucket elevator is inevitable. For this reason, analysis of failure is very crucial to the continuous improvement on the chain links which as a result will minimize down-time therefore increasing productivity. Whenever the chain link of the bucket elevator fail, it takes the technicians a minimum of three days depending on the severity of damage. This results in increased down-time which reduces production time coupled with damaged buckets and links which increases maintenance cost. The objective of this research is to analysis the cause of failure of the chain link of a bucket elevator by carrying out visual examination, chemical analysis and metallurgical analysis on failed chain link samples. Preliminary examination using stereo microscope revealed the type of fracture is a brittle fracture and chevron marks showed that the fracture began from the core of the fractured surface and progressed through the material until eventual fracture occurred. Metallurgical analysis revealed that the micro-structure is a tempered martensite and the material had a lot of cracks embedded within it which propagated during loading. Chemical analysis revealed that the carbon content was below the required standards and therefore does not meet the requirements.

Análisis de falla del disco de embrague de un camión de 2 ton

Este artículo muestra el análisis de la falla presentada en el disco de embrague de un camión para transporte de 2 Ton. El elemento que presentó la fractura estaba fabricado de acero para resortes de alto carbono. Aunque la zona de falla era muy delgada y de difícil interpretación, el examen de la superficie de fractura reveló marcas chevron y presencia mínima de marcas de playa muy tenues. La parte de falla (cushioning plate), fabricada de acero al carbono 1070 templado, estaba sometida a esfuerzos alternantes cortantes y flexión. La falla final fue causada por carga de impacto.

My Acid Cruise

My Acid Cruise Nancy Lord (bio) I thought I'd grow up to be a scientist. As a child I was infatuated with pet mice and guppies and studying trees from the shapes of their leaves. And don't I remember, as a kindergartner, being ushered into the school basement to watch on TV the Russian satellite, Sputnik, soaring into outer space? We were lectured on the spot to start studying science and math, or the Russians would pound us all into the ground. There was no higher goal than to reach for the stars or dive to the bottom of the sea, to comprehend the universe. The Alan Shepards and Jacques Cousteaus who did these things were our heroes. King science and its applied technology informed our lives and the promise that was the future. Who knew, in that bright and shining time, that so much in our culture and politics would soon turn corrosive? But along the way, I found that science—the actual doing of it— is tedious, at least compared with watching guppies eat their young. The collection of data is a repetitive business, the same careful measurements over and over, across hours and days, years, decades. You gain small increments of understanding—or perhaps not. Your only understanding may be one of failure: an inability to find pattern or meaning, the need for more data, additional data sets, a new theory. We don't have time for this. We're an impatient people. I'm speaking of Americans now. We don't trust science, in any case. We don't understand it, which is reason enough not to trust it or the people in the white coats who, surely, can manipulate numbers any way they want as part of that vast scientific conspiracy to get rich off government funding. Why spend tax dollars for a bunch of wonky people to measure cow farts or fuss over some bit of whatever floating around in the ocean? We know what we know, anyway. We don't need those fancy-pants, with their heads in clouds and all those crazy charts and numbers, to tell us how to live. But wait. We don't understand irony either. [End Page 90] Instead of a scientist, I became a writer of the creative sort, but then— wouldn't you know?—the fish and the trees and the stars all kept calling to me and, increasingly, seemed to demand attention for more than their own sakes. In a crowded, warming world, I was drawn back both to the wonders of nature and to wanting to better understand the systems we all rely on. And so I find myself, the lone writer among scientists, aboard the research vessel Tiglax, on Alaska's Seward Line. September along the southern coast is often stormy—not an ideal time to boat on the open ocean. But here I am. The Seward Line: an imaginary straight line that extends from the mouth of Resurrection Bay south of Seward, Alaska, 150 miles into the Gulf of Alaska, to where the continental shelf falls off into very deep water. The Seward Line: also the name of a long-term observation program that studies changes in the marine system, especially in relationship to climate variability. There are twenty-two stations spaced along the Line, and we—a team from the University of Alaska Fairbanks, made up mostly of volunteer graduate students, with a couple of professors and me, a writer invited to help bring some public awareness to the work—stop at each station to collect basic oceanographic data. When we finish, we duck into Prince William Sound and do the same at stations there. We are enormously lucky on this week-long cruise. The sea has been so calm that the other day we drifted with a pair of fin whales and could see, looking down through the glassy blue surface, the entire body length of the whales as they passed by and under us. The larger one, when it lined up beside us, approached our own 120-foot length. Pale chevron markings descended its dark back. Its white right jaw, distinct from its dark left one, flashed...

Interpretation and significance of reverse chevron-shaped markings on fracture surfaces of API X100 pipeline steels

Fracture surfaces of X100 pipeline steels were examined with optical and electron microscopy after crack tip opening angle fracture testing. Some fracture surfaces exhibited chevron-shaped fracture patterns that are markedly different from classic chevron fracture. The chevron-shaped markings on the X100 fracture surfaces point in the direction of crack growth, rather than towards the location of fracture initiation, as observed in classic cases of chevron fracture. Existing models, predicting formation of chevron fracture patterns, do not explain the fracture behavior observed for X100 steel. A mechanism is proposed where reverse chevron-shaped patterns are developed due to the shape of the crack front itself. The chevron shape forms as a result of crack tunneling, and the overall pattern is developed on the fracture surface due to intermittent crack growth, resulting in alternating regions (bands) of fast fracture and slower, more ductile fracture. The contrast between these bands of alternating fracture defines the chevron. Care should be taken during interpretation of intermittent chevron markings on fractures of ductile materials, as they may point away from rather than towards the origin of fracture.

Evaluation of Effectiveness of Converging Chevron Pavement Markings in Reducing Speed on Freeway Ramps

Converging chevron pavement markings have recently seen rising interest in the United States as a means to reduce speeds at high-speed locations and improve safety performance. This paper reports on an investigation into the effectiveness of chevron markings in reducing vehicle speeds on two-lane freeway-to-freeway directional ramps in Atlanta, Georgia. The evaluation is based on a statistical comparison at preselected sites of speeds before and after the installation of the chevron markings. The analysis focuses on the effect of converging chevrons over the range of speed percentiles and on the mean speed. The analysis indicates that chevrons have a minimal effect on vehicle speeds, with drivers adjusting back to their previous speeds as they acclimate to the treatment. The effect of the chevrons’ treatments on speed tended to be most pronounced immediately after the chevron implementation. However, by the 9th month after implementation the magnitude of the effect dropped to under 1 to 2 mph for the mean speed and most vehicle speed percentiles. Although this result does not necessarily imply that the chevron treatment is not a meaningful safety treatment, any safety benefits are not likely to result from a general decrease in speeds.

Fracture analysis of collapsed heavy-duty pulley in a long-distance continuous conveyors application

In this paper we present a case study of a heavy-duty pulley that failed after 2.1 × 10 7 cycles. The pulley was installed as a take up on a continuous conveyor under a load of 350 kN transmitted by the counterweight tower. The failure was analyzed using (a) finite element analysis by Ansys, (b) field data analysis, and (c) fracture macro examination. The prior FEA analysis showed that the pulley was designed according to its field application and moreover when re-simulated, by applying higher loads, revealed high potential towards its safety factor. The field examination showed that the conveyor did not suffer any overload that would contribute to the pulley collapse. The macro failure analysis revealed stress discontinuities and fatigue symptoms such as beach marks and even chevron marks within the welding region. In the meantime the welding region did not show evidence of thermal affected zone (TAZ), which is the key to its mechanical strength. The case analysis showed that the pulley was designed in accordance with British Standard [British Standards Institution, BS 5400:1980. Steel, concrete and composite bridges: Part 10: code of practice for fatigue; 1980] but a welding failure generated unexpected stresses and weakness on the welding region which generated fatigue and the final fracture.

Fractographic and Metallographic Study of Spalling Failure of Steel Straightener Rolls

Spalled fragments from work rolls of a steel bar straightening machine were received for failure analysis. Visual inspection coupled with optical and scanning electron microscopy (SEM) were used as the principal analytical techniques for the investigation. Fractographic observations clearly revealed the presence of a characteristic fatigue crack propagation pattern (beach marks) and radial chevron marks indicating the occurrence of final overload through a brittle intergranular fracture mode. The collected evidence suggests strongly that surface-initiated cracks propagated by fatigue mechanism led to spalling, resulting therefore in severe work roll damage and subsequently high machine downtime and maintenance costs.

LME induced failure of a combat aircraft gun

Premature catastrophic failures of gun barrel casings of a combat aircraft were reported. Magnetic particle fluorescent (MPF) and die penetrant inspections of in-service casings indicated cracks in various locations. Further investigations unveiled them to be multiple initiation fatigue cracks. The fracture surface of the failed casings showed chevron marks pointing towards the crack origin, where Pb, Cu and Zn were present in high concentrations. The finding construed that the failures were anticipated by liquid metal embrittlement.

The role of defects in the fracture of an Al–Si–Mg cast alloy

A study of the tensile behaviour of test coupons that were extracted from cast plates of D357 aluminium is described. The effects of specimen thickness, heat treatment, structural integrity and hot isostatic pressing (HIP) were investigated. Chevron marks were found on the fracture surfaces of the specimens that failed under plane strain conditions. In most cases, structural defects, such as shrinkage pores and oxide films, were found at the initiation sites for fracture. It is shown that the structural defects that were found at the origin of the chevron patterns are large enough to explain the fractures, and that the tensile failure of cast Al–7Si–Mg alloys can be explained in terms of the principles of fracture mechanics. The influence of structural defects on the elongation to fracture is discussed, together with some implications for quality control programs involving cast Al–7Si–Mg components.

Self-Affine Measurements on the Fracture Surface of Plastic Materials by AFM

AbstractThe self-aff'me behavior of fracture surfaces of polymeric materials was qualitatively and quantitatively studied. SEM images of fracture surfaces of both polypropylene and polystyrene show Chevron marks at several magnifications. In addition, for polystyrene the mirror and Hackle zones were also observed. For quantitative analysis, the average roughness exponent, ζ, of height profiles generated by AFM images, was estimated by applying the variable bandwidth method. Values of ζ=0.788 and ζ=0.810 were obtained for polypropylene and polystyrene, respectively. These results are in very good agreement with the claimed universal exponent of 0.8 reported in the literature for other non-polymeric materials. By choosing the AFM appropriate operating conditions, measurements of roughness on plastic material surfaces could be performed.