Basic Failure Mechanisms Research Articles

The Influence of Eccentricity on the Behaviour of Thin‐Walled Cold‐Formed Steel Members with Open Cross‐Sections under Compression

AbstractThin‐walled cold‐formed steel elements represent an attractive structural solution due to the fast manufacturing and erection time on site. Their small thickness leads to imperfection and eccentricities sensitivities. An experimental program was performed on short members with lipped channel cross‐section of 150×60×20×2 mm, subjected to (1) eccentric compression about the minor axis, in a range of eccentricities between −40 mm and +40 mm and (2) eccentric compression about the major axis, in a range of eccentricities between 0 mm and +90 mm. Shortening of all specimens was measured in two ways, i.e. (1) using the displacement gauge integrated with the machine crosshead beam and (2) from deformation fields obtained using Digital Image Correlation system (DIC). The quantitative results, presented as ultimate loads vs eccentricity curve, emphasize the influence of the eccentric load on the capacity of the element and on the type of plastic mechanism formation. Finite element analyses were performed to simulate the behaviour of short members in eccentric compression using the commercial FE software ABAQUS/CAE. Static non‐linear analyses were carried out in displacement control. Both geometrical and material non‐linearities were included. The experimental results confirm two different basic failure mechanisms depending on the load eccentricity direction applied to the studied members with open cross‐section.

Rockfall hazard assessment of the Monte Gallo Oriented Nature Reserve area (Southern Italy)

The Monte Gallo area is a carbonate relief that develops a significant nature reserve and highly attracts tourism to the urbanized area of the City of Palermo (Southern Italy). The slopes are affected by several rockfall events, which have also caused death, injuries, material damage, and a strong social and economic impact. Here, a detailed geological and geotechnical study to assess the rockfall hazard relating to two sectors of the mount has been carried out. The hazard assessment at the slope scale was performed based on geological, geomorphological, geomechanical, and seismic analysis. Using both analytical and empirical methods and by means of different software, the reconstruction of the propagation areas for the eastern sector of the Mount was possible. Results were used to better understand the overall structure, characterize the rockfall source areas’ kinematics, and recognize the basic failure mechanisms. The obtained runout areas were compared with each other and with those of previous studies conducted in a neighboring area, as well as with the corresponding hazard area maps of the official cartography, which is being updated. It is expected to be supplemented with maps derived from empirical models.

Mechanical behaviour of additive manufactured 316L f2ccz lattice structure under static and cyclic loading

Additive Manufacturing (AM) provides new freedom of constructive possibilities for design engineers. Many structures with features like cavities or thin beams are difficult to be manufactured using conventional methods such as casting or machining while AM can ease this difficulty. Nevertheless, the various parameters that can influence the fatigue and structural behavior of the AM metals should not be neglected. So far, there are only a few studies on the influence of process parameters on the failure of lattice structures under fatigue loading. For this perspective, this article presents the manufacturing of lattice structures, and investigates basic failure mechanisms at the meso and macro levels. Within this framework, the process parameters of Laser-Powder Bed Fusion (L-PBF) are initially varied in order to influence the structure and to set it in a targeted manner. The varied process parameters are three different laser powers with adjusted speeds, which are applied to the additively manufactured samples. Static bending and cyclic axial loading are performed to investigate the mechanical strength of the specimens.

Failure mechanism transition of 3D-printed biomimetic sutures

Inspired by the biological sutures in nature, triangular suture specimens with different tooth tip angle and material combinations were fabricated via multi-material 3D printing. From mechanical experiments under uni-axial tension, two basic failure mechanisms were observed: tooth breakage and the cohesive failure of the interfacial layer. It was found that when the tooth tip angle increases and/or the strength of the material in the interfacial layer increases, the failure mechanism of sutures can transit from tooth breakage mode to the cohesive failure of the interfacial layer. To further understand the different failure mechanisms of sutures, advanced nonlinear finite element simulations were performed. The finite element models can predict both the overall load-displacement relation and the failure mechanisms of the 3D printed sutures.

The performance of paving block structures with mortar filled joints under temperature loading, accessed by means of numerical simulations

Paving block structures with mortar filled vertical joints can exhibit a significantly higher load capacity as comparable structures with sand filled joints. For this reason, this pavement construction method is increasingly being used or would be used, respectively, if its performance could be estimated reliably. Specifically, the exact cause of cracks due to cooling in winter has not been fully understood yet and appropriate prediction tools do not exist. This motivated the development of a numerical simulation tool for such paving block structures under temperature loading, which is able to take the brittle failure mechanisms in-between paving blocks and paving blocks and the underlying mortar bed into account. By means of the proposed simulation tool in this paper, basic structural failure mechanisms of such paving block structures, due to different temperature events, could be identified and relationships between crack widths and different bonding strengths as well as installation temperatures were obtained. Finally, estimates for necessary bonding strengths between paving blocks and mortar bed to prevent large (visible) cracks due to temperature loads are given.

Effects of rainwater softening on red mudstone of deep-seated landslide, Southwest China

Red mudstone landslides are widespread in southwest of China. The development and distribution of deep-seated landsides with slow inclination are closely related to the special soft rock properties of the red mudstone layers. Most previous studies focused on the failure mechanisms of rain-induced shallow landslides. Studies on deep-seated landslides in red layer zones are still limited. In order to ascertain the basic failure mechanisms of red layer landslides with a gentle inclination, a fatal landslide named as Shibangou landslide, which occurred in Sichuan, China, was investigated. This paper aims to (1) conduct laboratory tests on the reduction in shear strength of a red layer to identify the water–rock coupling effect; (2) investigate variations in the microscopic structure of the soft rock found within a red layer after rainfall infiltration; (3) discuss the failure mechanisms of red layer landslides with slow inclination. Results from shear test of mudstone from the Shibangou landslide revealed that there is a tendency that behavior of soft rock can be transferred to soil in different days of immersion. The delineation threshold of shear strength of the red layer is determined as 6days of immersion. Microstructures of clay minerals become loose and porous due to the contacts between the particles transferred from the face–edges, face–face associations into edge–edge, and face–edge associations. Therefore, the intramolecular and cemented expansions of illite are the basic mechanisms which lead to structural damage, structural decay, and strength attenuation of soft rock in red layer under the condition of rainwater infiltration.

Shear Strength of Arch-Shaped Members without Transverse Reinforcement

Arch-shaped members are used in many reinforced concrete structures such as tunnels, bridges, silos, or offshore constructions. They are generally designed to carry significant axial forces, and, in most cases, are not provided with transverse reinforcement. Depending on the applied actions, however, bending moments and shear forces may also develop. This can potentially lead to spalling failures of the concrete cover or to shear failures where the strength may be reduced in comparison with straight members. Such reduction is due to the curvature of the element and to the corresponding deviation forces originated by the compression and tension chords. In spite of the significance of the topic, little research has been performed. In this paper, the authors summarize the results of a comprehensive investigation comprising an experimental part on nine arch-shaped specimens with thickness equal to 400 mm (15.7 in.). On the basis of these results, the basic failure mechanisms and shear-transfer actions are identified. By using the principles of the critical shear crack theory for assessment of the shear strength, a design approach for such members is presented that accounts for the various mechanical and geometrical parameters. The approach provides consistent and accurate predictions when compared with the tests presented in the paper.

Traditional cob wall: response to flooding

PurposeThe influence of flood conditions upon traditional cob construction is little understood. This paper aims to investigate the ability of cob materials to resist flood situations and documents basic failure mechanisms. This work also seeks to investigate the wettability characteristics of cob materials utilising environmental scanning electron microscopy.Design/methodology/approachThis paper takes the form of a literature review and case study underpinning laboratory experiments.FindingsCob walls that are suitably compacted, straw reinforced and are composed and manufactured of the correct materials appear to have the ability to resist total failure when subjected to initial flood conditions, however, the duration to which these structures will remain intact has still to be ascertained, and testing is ongoing. A correlation appears to exist between the rate of cob material's compaction and the duration to which the structural integrity of the walls was retained when the samples were submerged in water. In addition, the use of straw reinforcing increased the duration to which the wall could be submerged before failure. Un‐reinforced cob walls that were submerged in simulated floodwaters, exhibited an undercutting pattern of deterioration prior to failure. The materials for cob construction exhibited both hydrophobic and hydrophilic characteristics. This would have an influence on the material's ability to saturate and dehydrate, and also have an impact on moisture transfer mechanisms. Unsaturated cob wall/samples developed surface tension between hydrophilic surfaces and this is believed by the authors to increase inter‐particle bond strength within the material by the suction effect.Originality/valueThis paper is believed to be the first preliminary investigation into the effect of flooding on cob structures. Additionally, it utilises environmental scanning electron microscopy to reveal information about the surface characteristics of the materials and uses wettability studies to assess the hydrophilic and hydrophobic nature of the aforementioned.

Deformation mechanisms and mechanical properties of modified polypropylene/wood fiber composites

AbstractMechanical properties and deformation mechanisms of polypropylene (PP)/wood fiber (WFb) composites modified with maleated polypropylene as compatibilizer and styrene‐butadiene rubber (SBR) as impact modifier have been studied. The addition of maleated polypropylene to the unmodified polypropylene/wood fiber composite enhances the tensile modulus and yield stress as well as the Charpy impact strength. SBR does not cause a drop in the tensile modulus and yield strength because of the interplay between decreasing stiffness and strength by rubber modification and increasing stiffness and strength by good interfacial adhesion between the matrix and fibers. The addition of both maleated polypropylene and rubber to the polypropylene/wood fiber composite does not result in an improvement of effects based on maleated polypropylene and rubber, which includes possible synergism. The deformation mechanisms in unmodified polypropylene/wood fiber composite are matrix brittle fracture, fiber debonding and pullout. A polymeric layer around the fibers created from maleated polypropylene may undergo debonding, initiating local plasticity. Rubber particle cavitation, fiber pullout and debonding were the basic failure mechanisms of rubber‐toughened polypropylene/wood fiber composite. When maleated polypropylene was added to this composite, fiber breakage and matrix plastic deformation took place. Polym. Compos. 25:521–526, 2004. © 2004 Society of Plastics Engineers.

The Pursuit of the Small: From Grain-Boundary Cavities to Nanocrystalline Metals

AbstractThe following article is based on the Von Hippel Award presentation given by Julia Weertman of Northwestern University on December 3, 2003, at the Materials Research Society Fall Meeting in Boston.Weertman received the award for “her lifelong exceptional contributions to understanding the basic deformation processes and failure mechanisms in a wide class of materials, from nanocrystalline metals to high-temperature structural alloys, and for her inspiring role as an educator in materials science.” It has been said that “the best things come in small packages,” and that is certainly in Weertman's mind in this presentation.She has spent much of her career “in pursuit of the small.” In this article, she first looks back at her experiences studying grain-boundary cavities and life in the spaces between grains.She then fast-forwards to modern work on nanocrystalline mechanical behavior, confirming that such nanocrystalline materials are indeed strong, but also brittle.Some of her experiences in studying these phenomena are also described.

INVESTIGATION OF SINGLE-EVENT TRANSIENTS IN FAST INTEGRATED CIRCUITS WITH A PULSED LASER

This paper describes the use of a pulsed laser for studying radiation-induced single-event transients in integrated circuits. The basic failure mechanisms and the fundamentals of the laser testing method are presented. Sample results are presented to illustrate the benefits of using a pulsed laser for studying single-event transients.

New Fatigue Data for Wind Turbine Blade Materials

This paper reports on recent fatigue data of interest to the wind turbine industry in several areas: (a) very high-cycle fatigue data; (b) refined Goodman Diagram; (c) effects of fiber waviness; and (d) large-tow carbon fibers. Tensile fatigue results from a specialized high-frequency small strand testing facility have been carried out to 1010 cycles in some cases, beyond the expected cycle range for turbines. While the data cannot be used directly in design due to the specialized test specimen, the data trends help to clarify the proper models for extrapolating from standard coupons to higher cycles. The results for various fiber and matrix systems also provide insight into basic failure mechanisms. For spectrum loading predictions, a more detailed Goodman Diagram has been developed with additional R-values (R is the ratio of minimum to maximum stress in a cycle). The data of greatest interest were obtained for tensile fatigue with low cyclic amplitudes, close to R=1.0, to clarify the shape of the diagram as the cyclic amplitude approaches zero. These data may significantly shorten lifetime predictions compared with traditional Goodman Diagram constructions based on more limited data. The effects of material/process induced flaws on properties continues to be a major concern, particularly with large-tow carbon fabrics. The results of a study of fiber waviness effects on compressive strength show significant strength reductions for severe waviness which can be introduced in resin infusion processes. The final section presents new fatigue results for large-tow carbon/fiberglass hybrid composites. Epoxy resin laminates show marginally higher compressive strength and fatigue resistance with carbon fibers. Improved compressive static and fatigue performance is found with stitched fabrics as compared with woven fabrics.

The ballistic failure mechanisms and sequence in semi-infinite. supported alumina tiles

The basic ballistic failure mechanisms and their sequence occurring in dense alumina tiles during projectile penetration were investigated. The alumina tiles were supported by semi-infinite support blocks made of three different materials. Initially, a drop-weight test (DWT) was used to gain an insight into the damage mechanisms and sequence during quasi-static impact conditions. The quasi-static damage mechanisms were compared with the damage obtained in 0.3 cal. armor-piercing tests (APT). The DWT's results suggested the following sequence of quasi-static failure mechanisms: Radial tensile cracks, associated with the low tensile strength of the ceramic formed initially, as a result of the bending induced by local deformation at the opposing surface. Subsequently, a shear-dominated cone crack propagated from the edge of the contact zone. If sufficient energy was available, crushing of the material beneath the contact zone developed during the final stages of failure. It is shown that these so-called “quasi-static” damage mechanisms, identified from the DWT's, also corresponded to the damage mechanisms and sequence during APT's.

Mechanical reinforcement and geotechnical design of open pit mine using DEGRES program

ABSTRACT The DEGRES program is a computational tool to help with decisions about geometrical design and geotechnical studies in open pit mining and quarrying. Firstly, it automatically provides a geometrical model of a pit from a basic contour plane. Secondly, a haul road can be inserted into the geometrical model. Finally, in association with geological and geotechnical models of the ore body, various basic failure mechanisms are analyzed for the total or partial height of each pit side. Regarding the calculated safety factors and volumes of unstable rock masses, mechanical reinforcement with tensioned anchors can be studied.

The reliability of laser diodes and laser transmitter modules

This paper reviews the reliability of laser transmitter modules for use in optical fibre transmission systems. Methods for reliability testing and lifetime prediction are discussed and the dominant failure mechanisms affecting laser modules are described. The current status of laser module reliability is discussed, based on both published results, and on the findings of a study at BT Laboratories of the reliability of commercial laser modules from ten manufacturers. It is concluded that significant progress has been made in the reliability of laser diodes, through the understanding of basic failure mechanisms, leading to long predicted lifetimes for a number of different laser structures. However, module packaging is less reliable and further work is required to identify and eliminate those materials and processing technologies which lead to the risk of early failure.

Eccentrically Connected Cleat Plates in Compression

This paper investigates experimentally and theoretically the ultimate compressive capacity of eccentrically connected cleat plates. Because of the eccentricity in the connection, significant bending stresses are developed in the plate from the onset of loading. The first yield approach is extremely conservative and does not predict accurately the ultimate behavior of the connection. Analysis based on buckling of the cleat plate alone, without consideration of moments induced in the cleat plate due to eccentricity, leads to unconservative predictions. A limit analysis is proposed, based on the plastic collapse approach with allowance for reduction in the plastic moment capacity due to the effect of axial load. A number of basic failure mechanisms are identified. Formulas for predicting the ultimate compressive capacity of eccentrically connected cleat plates, whose ends are fixed and prevented from sway, are derived, and 22 test specimens of varying cleat‐plate thicknesses and lengths are tested to failure. The predicted ultimate compressive loads and failure modes obtained are in good agreement with experimental findings.

The physical basis for the roller‐coaster hazard rate curve for electronics

AbstractThis is the final installment of a series of three articles under the general topic ‘Off the bathtub onto the roller‐coaster curve’. A short version was presented at the 1988 Annual Reliability and Maintainability Symposium in the U.S.A. The first article was entitled ‘The bathtub does not hold water any more’, and the second was entitled ‘The roller‐coaster curve is in’. The three articles provide detailed discussions of the findings leading to the conclusions on the roller‐coaster characteristics for the hazard rate curve for electronics. The first article discussed the problems with the bathtub and the second explored the shape of the hazard rate curve in view of some recent observations. This article suggests some plausible physical reasons for the formation of the roller‐coaster shape. The generation of the shape starts with the basic failure mechanisms, which leads to the generally decreasing hazard rate. The humps could be caused by changing hazard conditions, wear‐out failure distribution of flawed items, distribution of flaw sizes or residue small size flaws left in the equipment because of test and inspection limitations.

Dynamic behavior of a boron carbide aluminum cermet: experiments and observations

Experimental techniques to study and characterize the dynamic behavior of ceramics and ceramic composites are described. A new technique based on the split Hopkinson pressure bar is used to obtain the deformation and failure characteristics of brittle materials at moderately high strain rates. A normal plate impact recovery technique is used to study the evolution of damage under controlled loading conditions and understand the micromechanisms of damage in materials. The normal plate impact recovery technique has the advantage of applying sufficiently high stress levels to initiate damage and yet providing controlled amounts of energy input to avoid catastrophic failure of the material. Hence, the samples can be recovered intact and evaluated for damage using standard characterization techniques such as microscopy and ultrasonics. The damage assessment in the material together with the real-time interferometric measurements serves as a powerful experimental procedure to study processes such as damage initiation, damage evolution, and the failure modes of very hard and brittle ceramics and ceramic composites under stress wave loading. Results are presented for a boron carbide aluminum cermet, a ceramic composite and the role of its microstructure on the failure mechanisms is studied. The cermet exhibits high strength and large strain to failure, in comparison to monolithic ceramics. The basic failure mechanisms in the cermet appear to be axial microcracking due to compression, and transverse cracking generated by compression release and by tension. The cracks are also found to be bridged by ductile aluminum or intermetallics, which together with the microcracking could possibly increase the toughness of the cermet at high loading rates.

The Mechanics of Short Fiber-Reinforced Composites: A Review

Abstract Proper constitutive equations and transformation laws to describe short-fiber-reinforced composites have been reviewed. The mechanisms of load transfer between matrix and fibers have been presented. Micromechanics analyses were discussed in order to predict mechanical properties of the composite given those of the constituents. Such approaches have been used successfully for cord-rubber and particulate-filled elastomeric composites. The use of such methods for short-fiber reinforcement has been limited so far. The problem is more complex in this case, but the need for a reliable method is even stronger in order to evaluate the influence of a parameter change on the various mechanical properties. Elastomeric composites pose a greater change due to the large ratio of fiber-to-matrix moduli, and predictions may not always be accurate. However, the interest of micromechanics approaches is that they allow determination of the effect of a perturbation in the parameters about a given level. Areas for future work include the development of micromechanics methods to determine viscoelastic constants and strength under various loading conditions. The development of a multiaxial strength criterion is needed, and basic fatigue failure mechanisms have to be studied.

Implosion Strength of Cylindrical Concrete Shells: A Comparison of Theoretical and Experimental Results

Offshore concrete production and storage facilities sustain maximum hydrostatic pressure during submergence for deck installation. The failure mode associated with this critical load condition is termed implosion. This paper describes an analytical technique for determining the implosion strength of concrete cylindrical shells. Introduction Large concrete structures are being used as drilling and/or production platforms in the North Sea (Fig. 1). These structures are called gravity platforms because they are maintained on location by the weight of the structure and entrained ballast material. The platform base or caisson typically has a cellular configuration that serves to provide buoyancy for adequate payload capacity during tow and also may serve o provide oil storage. The critical design load condition for the caisson occurs during the submergence sequence for installation of the deck, when the caisson cells are subjected to maximum hydrostatic pressure. The potential failure mode for this condition is termed implosion and may result from structural instability, inadequate shear capacity at discontinuous junctures of shell segments (i.e., structural end closures on cells), or general material failure. This paper deals only with the instability and general material failure mechanisms. The calculation methods used pertain to a single cell and do not address directly the "grouping effect" of the multicellular caisson. This, approach does, however, yield insight into basic failure mechanisms that may be extended to more complex structures.The paper summarizes an historical review of solutions for the stability of cylindrical shells under various load conditions. Gerard's development of a theoretical plasticity reduction factor based on a modified form of Donnell's equation is described. The applicability of a theoretically derived plasticity reduction factor in stability calculations for simply supported, unreinforced concrete cylinders is established by comparison with experimental data. The influence of the end constraints on the cylinder is examined using the MARC finite element program. Finally, an analytical technique incorporating second-order geometry effects is described whereby the influence of out-of-roundness on the implosion strength of plain and reinforced concrete shells may be evaluated. Literature Survey The stability of cylindrical shells subjected to hydrostatic pressure has been a subject of considerable interest since the turn of the century. As early as 1911, Lorenz presented solutions for cylinders subjected to axial compression. Southwest in 1913 and Von Mises in 1914 published solutions for buckling under uniform lateral pressure. Von Mises followed in 1929 with a solution for the combined load case of axial compression and uniform lateral pressure (simple hydrostatic pressure). Flugge in 1932 addressed stability under pressure). Flugge in 1932 addressed stability under combined loading and bending. Stability under torsional loading was investigated by Schwerin in 1925 and Donnell in 1933. JPT P. 27