Low Deformation Levels Research Articles

Lithosphere strain rate and stress field orientations near the Alpine arc in Switzerland

In this study we test whether principal components of the strain rate and stress tensors align within Switzerland. We find that 1) Helvetic Nappes line (HNL) is the relevant tectonic boundary to define different domains of crustal stress/surface strain rates orientations and 2) orientations of T- axes (of moment tensor solutions) and long-term asthenosphere cumulative finite strain (from SKS shear wave splitting) are consistent at the scale of the Alpine arc in Switzerland. At a more local scale, we find that seismic activity and surface deformation are in agreement but in three regions (Basel, Swiss Jura and Ticino); possibly because of the low levels of deformation and/or seismicity. In the Basel area, deep seismicity exists while surface deformation is absent. In the Ticino and the Swiss Jura, where seismic activity is close to absent, surface deformation is detected at a level of ~2 10−8/yr (~6.3 10−16/s).

Adaptive reorientation of endothelial collectives in response to strain.

Mature epithelial monolayers share the ability to coherently respond to external mechanical stimuli. Tissue remodeling requires cell shape changes and coordinated movements. Human endothelia provide an exquisite example of such emerging collective activities. As part of their function in maintaining body homeostasis under variable hemodynamic loadings, endothelial ensembles must dynamically adapt to wall shear stress and cyclic deformation. While the alignment of several types of cells, including fibroblasts, osteoblasts and epithelial tissues, in response to various flow conditions or wall shear stress levels has been described in detail, less is known about collective endothelial remodeling under pure wall deformation. Here, using a custom-developed bioreactor, we exposed mature human endothelia to two distinct physiological levels of cyclic loading, generating overlapping gradients of strain. Endothelial cells remodeled depending on the level of imposed strain yielding local variations of cell density. In particular, a collective cell orientation orthogonal to the main direction of strain was observed at low levels of wall deformation, while cells reoriented parallel to the main direction of strain at high levels of wall deformation. The tissue adaptation depended on the establishment of mature adherens junctions, which were reinforced by the polarized recruitment of the adaptor protein vinculin. The pivotal role of cell-to-cell junctions was confirmed by the biochemical inhibition of vascular endothelial cadherin homotypic contacts, which impaired the collective remodeling. Together, our data establish wall deformation as an independent determinant of endothelial architecture with direct implications in vascular physiopathology.

Retracted: 01.01: Placement of nut determining failure mode of bolt and nut assemblies

ABSTRACTBolt and nut assemblies under tension loading can either fail by bolt fracture or thread failure. The latter failure mode is arguably undesired because it leads to failure at a comparatively low deformation level. Moreover, incipient thread failure is challenging to detect in the case of over‐tightening since the bolt remains in the bolt hole after this type of failure occurs. The failure mode of bolt and nut assemblies is determined by several well‐known factors such as the thread engagement length and the relative strength of the bolt and nut. However, one factor that has received limited attention in the literature is the placement of the nut along the threaded portion of the bolt shank. We have performed a series of direct tension tests on various single M16 bolt and nut assemblies, where the placement of the nut was varied. Some of the assemblies experienced that placing the nut close to the thread run‐out, i.e., near the unthreaded portion of the bolt shank, led to thread failure, whereas placing the nut sufficiently far from the thread run‐out led to bolt fracture. We carried out finite element simulations of the tests in order to further investigate the mechanisms occurring during failure. In the case where the nut was located close to the thread run‐out, the simulations revealed that necking of the bolt shank affected the effective overlap of the internal and external threads. This effect seemed to contribute to thread failure in both tests and simulations.

How placement of nut determines failure mode of bolt-and-nut assemblies

Bolt-and-nut assemblies under tension loading can either fail by bolt fracture or thread failure. The latter failure mode is arguably undesirable because it leads to failure at a comparatively low deformation level. Moreover, incipient thread failure is challenging to detect in the case of over-tightening since the bolt remains in the bolt hole after this type of failure occurs. The failure mode of bolt-and-nut assemblies is determined by several well-known factors such as the thread engagement length and the relative strength of bolt and nut. However, one factor that has received limited attention in the literature is the placement of the nut along the threaded portion of the bolt. We have performed a series of direct tension tests on various single M16 bolt-and-nut assemblies where the placement of the nut was varied. Some of the assemblies experienced that placing the nut close to the thread run-out, i.e. near the unthreaded portion of the bolt (the shank), led to thread failure, whereas placing the nut sufficiently far from the thread run-out led to bolt fracture. We carried out finite element simulations of the tests in order to investigate further the mechanisms occurring during failure. In the case where the nut was located close to the thread run-out, the simulations revealed that necking of the bolt affected the effective overlap of the internal and external threads. This effect seemed to contribute to thread failure in both tests and simulations.

Large elastocaloric effect at small transformation strain in Ni45Mn44Sn11 metamagnetic shape memory alloys

The elastocaloric effect has been investigated by directly measuring temperature change in Ni45Mn44Sn11 metamagnetic shape memory alloys. The stress plateau for magnetostructural transition can be drastically reduced due to the mechanical training effect. A large temperature change of 4K was found during compressing the sample with a small transformation strain of 1.3% at 291.5K. Our results indicate that Ni–Mn–Sn alloys can be a promising candidate for solid-state refrigerants in mechanical cooling application by low deformation level.

Experimental validation of a numerical model for predicting the trajectory of blood drops in typical crime scene conditions, including droplet deformation and breakup, with a study of the effect of indoor air currents and wind on typical spatter drop trajectories

Bloodstain Pattern Analysis (BPA) provides information about events during an assault, e.g. location of participants, weapon type and number of blows. To extract the maximum information from spatter stains, the size, velocity and direction of the drop that produces each stain, and forces acting during flight, must be known.A numerical scheme for accurate modeling of blood drop flight, in typical crime scene conditions, including droplet oscillation, deformation and in-flight disintegration, was developed and validated against analytical and experimental data including passive blood drop oscillations, deformation at terminal velocity, cast-off and impact drop deformation and breakup features. 4th order Runge–Kutta timestepping was used with the Taylor Analogy Breakup (TAB) model and Pilch and Erdman's (1987) expression for breakup time. Experimental data for terminal velocities, oscillations, and deformation was obtained via digital high-speed imaging. A single model was found to describe drop behavior accurately in passive, cast off and impact scenarios.Terminal velocities of typical passive drops falling up to 8m, distances and times required to reach them were predicted within 5%. Initial oscillations of passive blood drops with diameters of 1mm<d<6mm falling up to 1.5m were studied. Predictions of oscillating passive drop aspect ratio were within 1.6% of experiment. Under typical crime scene conditions, the velocity of the drop within the first 1.5m of fall is affected little by drag, oscillation or deformation.Blood drops with diameter 0.4–4mm and velocity 1–15m/s cast-off from a rotating disk showed low deformation levels (Weber number<3). Drops formed by blunt impact 0.1–2mm in diameter at velocities of 14–25m/s were highly deformed (aspect ratios down to 0.4) and the larger impact blood drops (∼1–1.5mm in diameter) broke up at critical Weber numbers of 12–14. Most break-ups occurred within 10–20cm of the impact point. The model predicted deformation levels of cast-off and impact blood drops within 5% of experiment. Under typical crime scene conditions, few cast-off drops will break up in flight. However some impact-generated drops were seen to break up, some by the vibration, others by bag breakup.The validated model can be used to gain deep understanding of the processes leading to spatter stains, and can be used to answer questions about proposed scenarios, e.g. how far blood drops may travel, or how stain patterns are affected by winds and draughts.

Flow Lines, Microstructure, and Mechanical Properties of Flow Control Formed 4032 Aluminum Alloy

The flow lines, microstructure, and mechanical properties of a flow control formed (FCF) 4032 aluminum alloy scroll plate were studied in this paper. The influence of back pressure on the formation process was investigated and a scroll plate with ideal shape and size accuracy was formed. The results show that with the increase of back pressure the formation of scroll wrap improves while the effective stress and extrusion load increases rapidly. Specific levels of back pressure have an application scope. The flow lines generally distribute along the shape of the scroll plate. The microstructures and mechanical properties of formed scroll plates were examined. The microstructure in the center of the scroll wrap exhibits obvious directionality and the Al grains are elongated along the extrusion direction. The microstructures of the end plate and top part of the wrap maintain cast structures because of low levels of deformation. The mechanical properties of scroll plate completely meet its operating requirements.

A numerical investigation of the interplay between cohesive cracking and plasticity in polycrystalline materials

The interplay between cohesive cracking and plasticity in polycrystals is herein investigated. A unified finite element formulation with elasto-plastic elements for the grains and interface elements for the grain boundaries is proposed. This approach is suitable for the analysis of polycrystalline materials with a response ranging from that of brittle ceramics to that of ductile metals. Crystal plasticity theory is used for 3D computations, whereas isotropic von Mises plasticity is adopted for the 2D tests on plane strain cross-sections. Regarding the grain boundaries, a cohesive zone model (CZM) accounting for Mode Mixity is used for the constitutive relation of 2D and 3D interface elements. First, the analysis of the difference between 3D and 2D simulations is proposed. Then, considering all the nonlinearities in the model, their interplay is numerically investigated. It is found that the CZM nonlinearity prevails over plasticity for low deformation levels. Afterwards, plasticity prevails over CZM. Finally, for very large deformation, failure is ruled by the CZM formulation which induces softening. The meso-scale numerical results show that the simultaneous use of cohesive interface elements for the grain boundaries and plasticity theory for the grains is a suitable strategy for capturing the experimental response of uniaxial tensile tests.

Experimental and finite element simulation study of the adiabatic shear band phenomenon in cold heading process

This paper presents the outcomes of a comprehensive experimental, metallurgical and finite element (FE) simulation study to characterize the development of adiabatic shear band (ASB) phenomenon in steel cold heading (CH) process. The main objective of this work is to investigate the complex interplay of different process and material parameters on the ASB development stages inside the cold headed parts.In this work, the drop weight compression test (DWCT) was selected to simulate the CH process impact loads on specimens machined from 1038 steel and 1018 steel. Series of DWCTs were performed under different impact loading conditions. The goal of these tests is to achieve different deformation levels and introduce ASBs at different stages.To reach a full understanding of this complex phenomenon, the FE simulation analysis was used to support the metallurgical examination of the DWCT specimens. The FE analysis provided important details about the changes of different material and process parameters at the critical zones inside the ASBs.This study confirmed that the ASB is mainly a thermo-mechanically controlled phenomenon. The ASBs develop in three stages: homogeneous plastic strain, inhomogeneous plastic strain, and strain localization. The ASB development stage depends mainly on the status of the competition between the work hardening and the thermal and geometrical softening mechanisms inside the bands. The domination of the softening mechanisms at advanced levels of deformation triggers a self-catalytic strain localization and material strength degradation process that leads to failure inside the band.In general, the metallurgical and finite element analysis investigation revealed that under impact loads, three ASBs can develop simultaneously inside the cold headed parts; lower, upper and central ASBs. As the deformation continues; the development of the lower and upper bands slows down and contributes in the rapid development of the adjacent central ASB. This study confirmed that the ASB has a canonical structure which leads to an ASB that can experience different development stages along the same band simultaneously.This study proved that the shape and the type of ASBs in cold headed parts depend highly on material's properties. The metallurgical and finite element analysis revealed that the higher the strength of the tested steel, the easier to form a narrow ASB that reaches the localization stage at low deformation levels. In contrast, ductile steels experience wider ASBs when subjected to the same deformation levels. These bands require higher levels of deformation to reach the localization stage in comparison to higher strength steels.

Comparative study between large-scale and small-scale electrochemical potentiokinetic reactivation performed on AISI 316L austenitic stainless steel

This work optimizes the application of electrochemical potentiokinetic reactivation (EPR) to assess the degree of sensitization (DOS) of AISI 316L and compares the large-scale and small-scale EPR with the aim of improving the study of the different zones of AISI 316L welded joints by using an electrochemical minicell. The optimized EPR allows to discriminate better than the standardized EPR among different DOS. Small-scale EPR shows greater sensitivity to assess the DOS than large-scale EPR: (i) at lower deformation levels; (ii) for shorter sensitization times; (iii) when localized microstructural regeneration is caused by the combined effect of deformation and subsequent sensitization.

Effects of rolling reduction on mechanical properties anisotropy of commercially pure titanium

In the present work tensile and tear properties of commercially pure titanium with different rolling reductions and specimens directions were investigated. The experimental results showed that in low levels of deformation the microstructure refining and mechanical twins have fewer significant effects on the anisotropic behavior of both tear and tensile properties and the crystallographic texture controls the mechanical properties anisotropy. The increase in rolling reduction up to 50% led to the formation of strong-basal texture and resulted in the activation of almost same deformation systems and isotropic mechanical response. However, at high levels of deformation, due to the split distribution of basal texture and mechanical fibering, the anisotropy was again observed. It was found that loading modes strongly affect the dominant mechanisms which control the mechanical properties anisotropy.

Study of Inconel 718 weldability using MIG CMT process

This work investigates the weldability of Inconel 718 using the metal inert gas (MIG) welding process called ‘cold metal transfer’. This arc welding process is reported for working with a lower heat input compared to other arc processes. The consequences are less base metal impaired, low deformation and low residual stress level in assembly. In order to check these abilities, metallographic, texture, chemical and residual stress analyses have been carried out. Results show that MIG cold metal transfer has good properties for the welding of Inconel 718 inasmuch as no defect has been detected and a lower level of residual stresses has been introduced in metal compared to classic MIG.

Effect of precracking method on KIc results for medium-density polyethylene tested under cryogenic condition

The effect of different precracking methods on the results of linear elastic K Ic fracture toughness testing with medium-density polyethylene (MDPE) was investigated. Cryogenic conditions were imposed in order to obtain valid K Ic values from specimens of suitable size. Most conservative K Ic values were obtained by slow pressing a fresh razor blade at the notch root of the specimen. Due to the low deformation level imposed on the crack tip region, the slow pressing razor blade technique also produced less scatter in fracture toughness results. It has been shown that the slow stable crack growth preceding catastrophic brittle failure during K Ic tests in MDPE under cryogenic conditions should not be disregarded as it has relevant physical meaning and may affect the fracture toughness results.

Present-day stress-field modelling of southern Italy constrained by stress and GPS data

The present-day tectonic setting of the Italian peninsula is very complex and involves competing geodynamic processes. In this context, southern peninsular Italy is characterised by extension along the Apenninic belt and in the Tyrrhenian margin and by transpression in the Apulia–Gargano region. The extension is well defined by means of geological, seismological, and contemporary stress data. For the latter only few data are available in the Apulia–Gargano region, leaving the state of stress in that area unresolved. Here we develop a finite-element model of the southern Italian region in order to predict the contemporary stress field. Our model predictions are constrained by model-independent observations of the orientation of maximum horizontal stress ( S Hmax), the tectonic regime, and the horizontal velocities derived from GPS observations. We performed a blind test with 31 newly acquired S H max orientations in the Southern Apennines. These new data come from the analysis of orehole breakouts performed in 46 deep oil exploration wells ranging in depth from 1300 to 5500 m. The model results agree with the stress data that define a prevailing NW–SE S H max orientation along the Apenninic belt and foredeep and thus are capable to predict the stress field where no stress information is available. We first analyse how much model predictions, based on older data, deviate from present-day stress data and then recalibrate the models based on our new stress data, giving insight into the resolution of both models and data. In the studied region, which is affected by low deformation rates, we find that geodetic data alone cannot resolve such low levels of deformation due to the high relative measurement errors. We conclude that both GPS and stress data are required to constrain model results.

Why is the Ligurian Basin (Mediterranean Sea) seismogenic? Thermomechanical modeling of a reactivated passive margin

The seismic activity of the Ligurian Basin, the northeastern termination of the western Mediterranean basin, is larger than in surrounding regions, even though recent geodetic studies attest that this area is subject to very low levels of deformation. This basin is an example of a type of passive margins that cannot be considered solely as inert sites of sedimentation and of progressive subsidence and that are reactivated in a compressive pattern; other examples include the Kwanza basin (Angola) and the Brazil margin. We investigated, by means of 2‐D thermomechanical modeling, the structural and rheological heterogeneities that can lead to concentration of strain in this marginal basin. We deduced that the deformation of the basin is due to its particular geometric features, narrow and with a thick surrounding continental crust, related to its position at the southern termination of the Alps. This sharp transition, in terms of both geometry and rheological contrast, is a main factor in explaining the weakness of the margin. We discuss the importance of buoyancy forces versus tectonic forces, as well as thermal effects, on the observed reactivation. Influence of contrast in rheology between an oceanic‐type crust and continental crust is also studied. Geodynamical implications are proposed for the region. The good agreement between the predicted localized deformation and the observed seismicity distribution should help improve seismic hazard assessment in the region.

Experimental and finite-element analysis of scratches on amorphous polymeric surfaces

The scratch behaviour of two amorphous polymers is investigated to understand how the materials characteristics affect the scratch resistance. A thermosetting resin (CR39) and a thermoplastic polymer polymethylmethacrylate (PMMA) are studied using both an experimental set-up allowing in situ observations of the contact area during indentation or scratching with spherical tips, and a finite-element modelling (FEM). The rheological properties of CR39 and PMMA surfaces are modelled assuming a linear elastic behaviour and a plastic law with high strain hardening, described by G'sell Jonas equation. A description of the plastic strain field, beneath the indenter during scratch is proposed. The main parameter of the description is the level of the deformation imposed on the samples, related in first approximation to the ratio a/ R set between 0.1 and 0.4, a being the contact radius, and R the tip radius. The true friction μloc at the interface between the indenter and the material was modelled with a Coulomb's friction coefficient varying between 0 and 0.4, for each computed ratio a/ R. The two polymers display the same scratching behaviour for low levels of deformation, whereas at high strain, PMMA shows a more pronounced plastic behaviour, with high level of average plastic strain, especially for higher friction coefficient. This results obtained by FEM are in good correlation with experimental observations and show that the plastic strain gradient beneath the indenter depends clearly on the ratio a/ R, on the true friction coefficient and also the rheological parameters of tested material.

Cold-rolling induced amorphization in Cu–Zr, Cu–Ti–Zr and Cu–Ti–Zr–Ni multilayers

Amorphous Cu60Zr40, Cu55Ti35Zr10 and Cu47Ti35Zr10Ni8 alloys were synthesized at ambient temperature by repeated cold rolling with intermediate folding starting from a layered array of individual elemental sheets. A comparison was made of three kinds of glass-forming systems in terms of their glass-forming abilities during solid state processing. The microstructural development during the mechanical alloying process was investigated by X-ray diffraction, scanning and transmission electron microscopy. The progress of solid state reaction in different glass-forming systems was studied in detail at different deformation levels for a better understanding of the early stages of the crystal-to-amorphous transition during intense mechanical deformation. At the beginning of the solid state reaction i.e., at low deformation levels, the amorphous phase initially forms at the interlayer interface of the multilayers. The amorphous layer thickness increases with increasing deformation level and in the final stage of rolling, all samples transform almost completely to the amorphous state. The main key to the synthesis of a fully amorphous phase from pure elemental foils is the application of large deformation levels to overexceed the limit of critical solutal supersaturation for amorphization.

Influence of statistical and constraint loss size effects on cleavage fracture toughness in the transition – A model based analysis

A database derived from tests on specimens with a large range of ligament ( b) and thickness ( B) dimensions was systematically analyzed to evaluate constraint loss and statistical size effects on cleavage fracture toughness. The objectives were to: (1) decouple size effects related to constraint loss, mediated by b and B, from those arising from statistical effects, primarily associated with B; and, (2) develop procedures to transfer toughness data to different conditions of constraint and B. The toughness database for a Shoreham pressure vessel steel plate, tested at a common set of conditions, was described in a companion paper. Quantification of constraint loss was based on an independently calibrated 3D finite-element critical stress-area, σ ∗ - [ K J m / K J c ] , model. The measured toughness data, K J m , were first adjusted using computed [ K J m / K J c ] constraint loss factors to the corresponding values for small scale yielding conditions, K J c = K J m / [ K J m / K J c ] . The K J c were then statistically adjusted to a K J r for a reference B r = 25.4 mm. The B adjustment was based on a critically stressed volume criterion, modified to account for a minimum toughness, K min, consistent with modest modifications of the ASTM E 1921 Standard procedure. The combined σ ∗ - [ K J m / K J c ] - K min adjustment procedure was applied to the Shoreham b − B database, producing a homogeneous population of K J r data, generally within the expected scatter. The analysis suggests that: (1) there may be a maximum B beyond which statistical size effects diminish, and (2) constraint loss in the three-point bend specimens begins at a relatively low deformation level. A corresponding analysis, based on a Weibull stress, σ w - [ K J m / K J c ] - K min , adjustment procedure, yielded similar, but somewhat less satisfactory, results. The optimized adjustment procedure was also applied to other K J m data for the Shoreham plate from this study, as well as a large database taken from the literature. The population of 489 K J r data points, covering an enormous range of specimen sizes, geometries and test temperatures, was found to be consistent with the same master curve T 0 = −84 °C derived from the b − B database. Thus, calibrated micromechanical models can be used to treat size and geometry effects on K J m , facilitating using small specimens and data transfer to predict the fracture limits of structures.

Deformation and nano-rheology of red blood cells: An AFM investigation

Interaction forces, deformation and nano-rheology of individual red blood cells in physiologically relevant solution conditions have been determined by colloid probe atomic force microscopy (AFM). On approach of the physically immobilised cell and silica glass spherical probe surfaces, deformation of the red blood cell was observed in the force curves. At low levels of deformation, spring constants were determined in the range 3–6 mN m −1, whereas for higher levels of deformation, the forces increase non-linearly and on retraction, significant force curve hysteresis is observed (i.e. lower forces upon retraction). The extent of force curve hysteresis was dependent on both the drive velocity and loading force, typical of a viscoelastic system. The response of the red blood cell has been described by viscoelastic theory, where the short and long time scale elastic moduli and relaxation times are determined, i.e. the cell's nano-rheological properties elucidated. In addition to a time independent elastic modulus of 4.0 × 10 3 Nm −2 at low levels of deformation, time-dependent elastic moduli ranges are observed (3.5 × 10 4 to 5.5 × 10 4 Nm −2 at intermediate levels of deformation and 1.5 × 10 5 to 3.0 × 10 5 Nm −2 at higher levels of deformation). That is, one elastic and more than one viscoelastic response to the red blood cell deformation is evident, which is considered to reflect the cellular structure.

Influence of statistical and constraint loss size effects on cleavage fracture toughness in the transition—A single variable experiment and database

This paper, which is the first of two parts, describes a comprehensive experimental study to systematically measure constraint loss and statistical size effects on fracture toughness of a typical low alloy pressure vessel steel in the brittle-to-ductile transition. Both of these size effects lead to higher toughness in smaller specimens. Previous studies primarily involved specimens that differed in size, but with self-similar standard geometric configurations, making it difficult to separate constraint loss from statistical size effects. The focus here is on a single-variable database developed for a homogeneous plate section of the decommissioned Shoreham Reactor vessel steel, tested at the 3/4-plate thickness position. Tests were carried out at a common set of conditions and covered a full matrix of specimens with six thicknesses ( B) ranging from 7.9 to 254 mm and four widths ( W) ranging from 6.4 to 50.8 mm. The variations in B were designed to provide readily observable statistical sampling effects, while variations in W result in fracture at deformation conditions ranging from small scale yielding to those involving extensive loss of constraint. A detailed analysis of this database is presented in a companion paper, where physically based models are used to quantify the relative contributions of constraint loss and statistical size effects. The models also provide a general approach to adjusting measured toughness for both testing and applications. The B– W database and analysis also provides a comprehensive independent assessment of some key aspects of the master curve method in the ASTM E 1921 Standard discussed in detail elsewhere. In this paper, we present an empirical analysis that shows a high constraint toughness scaling with B that is reasonably consistent with ASTM E 1921, as well as effects of loss of constraint that occur at much lower deformation levels than reflected in the data censoring limit in ASTM E 1921.