Tensile and compressive responses of nociceptors in rat hairy skin.

In order to investigate mechanical behavior of red sandstone under cyclical compressive and tensile loads, a series of short-term uniaxial constant cyclical compressive and tensile loading tests and uniaxial constant cyclical compressive and tensile loading creep tests were conducted. First, based on the results of short-term uniaxial constant cyclical compressive and tensile loading experimental, the permanent residual strain, strains at peak stress were analyzed. Results show that the specimen shows permanent residual strain after suffering short-term cyclic loads; the residual strains and strains at peak stress show the “decay increase” and “steady-state increase” stages with the cyclic number N; the relationship between the strain at peak stress (tensile or compressive stress) and cyclic number can be well described by a modified Burger model. And then, in accordance with the creep experimental results, the creep behavior of the red sandstone was analyzed. Results show that there is obvious instantaneous strain, decay creep, and steady creep under each stress level of tensile or compressive stress stages; the specimen appears accelerated creep stage under the 5th tensile stress of 1.19 MPa. It was also found that power function can better express the relationship between steady strains and cycle number under tensile or compressive stress levels. In the end, a viscoelastic-plastic creep model was proposed; comparison of the test results with the proposed viscoelastic-plastic creep model predictions indicates that the proposed model is capable of describing the creep behavior of red sandstone subjected to cyclic tensile and compressive stress loading.

Polypropylene fiber reinforcement is an effective method to enhance the durability of concrete structures. With the increasing public interest in the widespread use of polypropylene fiber reinforced concrete (PFRC), the necessity of evaluating the mechanism of polypropylene fiber (PF) on the permeability of concrete has become prominent. This paper describes the influence of PF on the concrete permeability exposed to freeze-thaw cycles under compressive and tensile stress. The permeability of PFRC under compressive and tensile loads is accurately measured by a specialized permeability setup. The permeability of PFRC under compressive and tensile loads, the volume change of PFRC under compressive load, and the relationship between compressive stress levels at minimum permeability and minimum volume points of PFRC are discussed. The results indicate that the addition of PF adversely affects the permeability of concrete without freeze-thaw damage and cracks. However, it decreases the permeability of concrete specimens exposed to freeze-thaw cycles and cracking. Under compressive load, the permeability of PFRC initially decreases slowly and follows by a significant increase as the compressive stress level increases. This phenomenon correlates with the volume change of the specimen. The compressive stress level of the minimum permeability point and compressive stress level of the minimum volume point of PFRC exhibit a linear correlation, with a fitted proportional function parameter γ ≈ 0.98872. Under tensile load, the permeability of PFRC increases gradually with radial deformation and follows by a significant increase. The strain-permeability curves of PFRC under loading are studied and consist of two stages. In stage I, the permeability of PFRC gradually decreases with the increase of strain under compressive load, while the permeability increases with the increase of strain under tensile load. In stage II, under compressive load, the permeability of PFRC increases with the increase of freeze-thaw cycles, whereas under tensile load, the permeability gradually decreases with the increase of freeze-thaw cycles. The reduction of PF on the permeability of PFRC under tensile load is greater than that under compressive load. In future research, the relationship between strain and permeability of PFRC can be integrated with its constitutive relationship between stress and strain to provide a reference for the application of PF in the waterproofing of concrete structures.

Closure to “Discussion of ‘Yield Function for Solder Elastoviscoplastic Modeling’” (2005, ASME J. Electron. Packag., 127, pp. 147–156)

Mechanical stimuli interfere with cellular behaviors under many physiological conditions. To understand the role of mechanical stimuli, engineered devices are developed to apply mechanical loads to cells in vitro. Despite of their usefulness, these devices are limited since they often lack the capacity of spatial load control, which is essential for intercellular study. Moreover, application of both compressive and tensile loads using a single loading device is challenging. Here, we fabricate and characterize a microdevice for applying programmable compressive/tensile loads to live cells. The device consists of two PDMS substrates. The top substrate consists of nine circular membranes with patterned microdots array on the top surfaces. Each membrane is connected with a microfluidic channel built in the bottom substrate. Upon actuation, the fluid in the channels deforms the membranes and applies controllable strain to cells cultured on the membranes. In this design, each membrane can be individually controlled to apply desired strain levels. The surface strain of the PDMS membranes is characterized by mapping the displacement of the dot array. The result of strain analysis shows that, the radial strain at the center of a circular membrane upon deformation ranges from about 5% compressive strain to about 20% tensile strain, validating the capacity of the device in applying both tensile and compressive stresses. Cell testing is performed using trabecular meshwork endothelial cells. Cells on different membranes are subjected to 0.5Hz of compressive or tensile stresses. The result shows that compressive and tensile stresses have different effects on the cells, indicating the device a promising solution for cellular biomechanical study.

Uniaxial step loading test setup for determination of creep curves of oxidation-sensitive high strength materials in vacuum under tensile and compressive load

The objective of this program was to advance the fundamental understanding of thick thermal barrier coating (TTBC) systems for application to low heat rejection diesel engine combustion chambers. Previous reviews of thermal barrier coating technology concluded that the current level of understanding of coating system behavior is inadequate and the lack of fundamental understanding may impede the application of thermal barrier coating to diesel engines.(1) Areas of TTBC technology examined in this program include powder characteristics and chemistry; bond coating composition, coating design, microstructure and thickness as they affect properties, durability, and reliability; and TTBC "aging" effects (microstructural and property changes) under diesel engine operating conditions. Fifteen TTBC ceramic powders were evaluated. These powders were selected to investigate the effects of different chemistries, different manufacturing methods, lot-to-lot variations, different suppliers and varying impurity levels. Each of the fifteen materials has been sprayed using 36 parameters selected by a design of experiments (DOE) to determine the effects of primary gas (Ar and N2), primary gas flow rate, voltage, arc current, powder feed rate, carrier gas flow rate, and spraying distance. The deposition efficiency, density, and thermal conductivity of the resulting coatings were measured. A coating with a high deposition efficiency and low thermal conductivity is desired from an economic standpoint. An optimum combination of thermal conductivity and disposition efficiency was found for each lot of powder in follow-on experiments and disposition parameters were chosen for full characterization.(2) Strengths of the optimized coatings were determined using 4-point bending specimens. The tensile strength was determined using free-standing coatings made by spraying onto mild steel substrates which were subsequently removed by chemical etching. The compressive strengths of the coatings were determined using composite specimens of ceramic coated onto stainless steel substrates, tested with the coating in compression and the steel in tension. The strength of the coating was determined from an elastic bi-material analysis of the resulting failure of the coating in compression.(3) Altough initial comparisons of the materials would appear to be straight forward from these results, the results of the aging tests of the materials are necessary to insure that trends in properties remain after long term exposure to a diesel environment. Some comparisons can be made, such as the comparison between for lot-to-lot variation. An axial fatigue test to determine the high cycle fatigue behavior of TTBCs was developed at the University of Illinois under funding from this program.(4) A fatigue test apparatus has been designed and initial work performed which demonstrates the ability to provide a routine method of axial testing of coating. The test fixture replaces the normal load frame and fixtures used to transmit the hydraulic oil loading to the sample with the TTBC specimen itself. The TTBC specimen is a composite metal/coating with stainless steel ends. The coating is sprayed onto a mild steel center tube section onto which the stainless steel ends are press fit. The specimen is then machined. After machining, the specimen is placed in an acid bath which etches the mild steel away leaving the TTBC attached to the the stainless steel ends. Plugs are then installed in the ends and the composite specimen loaded in the test fixture where the hydraulic oil pressurizes each end to apply the load. Since oil transmits the load, bending loads are minimized. This test fixture has been modified to allow piston ends to be attached to the specimen which allows tensile loading as well as compressive loading of the specimen. In addition to the room temperature data, specimens have been tested at 800 Degrees C with the surprising result that at high temperature, the TTBC exhibits much higher fatigue strength. Testing of the TTBC using tension/compression cycling has been conducted using the modified test fixture. The goal of this work was to investigate the failure mechanisms of the coating and to determine if tensile and compressive fatigue damage would interact to influence the resulting life of the coating. Coating samples were run with various mean compressive loads and constant tensile loading approximately equal to 90% of the tensile strength of the coating. The results of this testing shows no interaction of failure resulting from the tensile and compressive load. The material fails in tension at the life predicted by the maximum tensile stress or in compression at the life predicted by the compressive stress. This indicates that there are two differing failure mechanisms for the TTBC in tension and compression.

Mechanosensitive nociceptors with unmyelinated axons (C-fibers) were studied in a preparation of isolated skin and nerve from rat. Afferent discharges were recorded while the skin was mechanically stimulated using quantitative stretch (tension) and indentation (compression). The apparatus allowed for generating stimuli of equal magnitudes in both tension and compression. Stimulus-response functions were obtained for individual afferents relating discharge rate to tensile stress or compressive stress. A response threshold and maximal slope were obtained from each function. Thresholds did not differ significantly for compression and tension nor did the maximal slopes. We conclude that C-nociceptors are equally sensitive to tensile and compressive stress.

To accurately evaluate the influence of the actual tension and compression state and stress ratio at the deck-to-rib welding seam position on the fatigue life of a bridge deck, this paper establishes a coupled stress analysis model that considers the welding residual stress and vehicle stress. Taking the Jiangyin Bridge as an example, a qualitative analysis of the fatigue life under the vehicle load and residual stress field is carried out using the proposed method. A case analysis showed that when the residual tensile stress in the welding seam position is superimposed on the mainly tensile cyclic vehicle load stress, the longitudinal stress relaxation exceeds the peak vehicle load stress; significant longitudinal stress relaxation occurred, while the transverse stress relaxation is not significant. However, when the residual tensile stress is superimposed on the mainly compressive cyclic vehicle load stress, the relaxations of both the longitudinal and transverse stresses are not obvious. Compared with the stress state of the welding point under the action of only the vehicle stress, when the coupling effect of the residual stress and vehicle stress is considered, i.e., the loading condition, the fatigue stress state of the weld point has undergone an essential change under cyclic compressive stress, that is, the compressive stress state that does not require a fatigue check is changed to the tensile stress state. Although the fatigue state of the tensile stress cycle condition has not changed, the fatigue life is reduced by varying degrees under either the compressive or tensile condition.

Effect of orientation and mode of loading on deformation behaviour of Cu nanowires

Over the past decade, the certified power conversion efficiency of perovskite solar cells (PSCs) has increased to 26.1%. However, phase instability originating from lattice strains, has limited their commercialization. Strains will inevitably be generated during the PSC fabrication and service process due to the “soft lattice” nature of halide perovskites. In particular, flexible PSCs are subjected to not only mechanical tensile and compressive loads, but also suffer from thermal stresses. In this study, strain-induced changes in the phase stability and the corresponding optoelectronic properties of CsPbI3−xBrx (CsPbI3, CsPbBr3, and CsPbI2Br) systems under tensile and compressive stresses were investigated using first-principles calculations. The results showed that compressive stresses reduce the bandgap value and increase the light absorption coefficient; thus, the optoelectronic performance is improved, whereas the light absorption coefficient decreases regardless of how the bandgap changes under tensile stresses. Moreover, under the same stress, the tensile strain value was twice that of the compressive strain, and the critical value of the transition from the cubic to tetragonal phase was lower, indicating that phase stability was worse under tensile stresses. Therefore, during the fabrication of PSCs, the tensile stress state should be adjusted to the compressive stress state, which is favorable for enhancing PSCs photovoltaic performance and phase stability. The results not only provide direct evidence of tensile and compressive strains influencing the phase stability and optoelectronic property changes in halide perovskites, but also highlight lattice-strain tailoring for the composition design, process optimization, and interface engineering of efficient and stable PSCs.

Heating of rock surface (e.g., flame heating) induces compressive stresses in the surface layer and tensile stresses of lower magnitude in the layer beneath. If the heating temperature is large enough (around 900 deg for shales), the compressive stresses initiate spallation produced by pre-existing cracks that and extensively grow parallel to the surface under compression. The extensive cracks separate thin layers from different parts of the heated surface which eventually buckle opening a new surface which starts being subjected to flame heating. Then the spallation process repeats itself producing a cavity of approximately cylindrical shape growing into the rock normal to the surface. The presentation reports the results of tests on flame heating of shales, which demonstrate that the spallation process is accompanied by emergence of a large tensile fracture normal to the surface. In order to check whether the fracture can be produced by tensile thermal stresses induced in the layer situated under the compressed layer we conducted a series of finite element simulations of thermal stresses for different spallation depths (depths of the cavity). The modelling shows that: (1) as the spallation cavity deepens the magnitudes of maximum compressive and tensile stresses remain approximately the same except of two peaks at the spallation depths of about 6% and 30% of the diameter of the heating flame; (2) the magnitude of the maximum tensile stresses is about half of the compressive stress. Given that the spallation strength is about half of the UCS (e.g., [1]) and that the tensile strength is often up to an order of magnitude lower than the UCS, the induced tensile thermal stresses can be considered as sufficient to produce the tensile fracture. The experiment and computer modelling suggest that the production of tensile fractures is an intrinsic feature of the spallation process. These results can assist in understanding large scale spallation-like processes in the Earth’s crust and design rock cutting based on thermal spallation. Wang, H., A.V. Dyskin, Pasternak, P. Dight and B. Jeffcoat-Sacco, 2021. Fracture mechanics of in-situ spallation. Engineering Fracture Mechanics, 260, 108186.

The addition of Al and Ga to b.c.c. α-Fe increases the magnetostriction of Fe in the [100] direction (a factor of 12 for Fe₈₁Ga₁₉). Fe-based magnetostrictive materials are machineable, mechanically tough and relatively inexpensive. They can be used with tensile loading and saturate in fields of only a few hundred Oe, even under compressive loads up to -100 MPa. The effects of annealing single crystal Fe_86.9Ga_4.1Al_9.0 and Fe_86.9Ga_8.7Al_4.4 and polycrystalline Fe_81.6Ga_18.4 rods under stress were examined. Stress annealing allows the material to achieve most of its strain without applying a prestress, simplifying device design. Most importantly, it allows the materials to operate magnetostrictively under a tensile load. Annealing was performed in a vacuum furnace with a -100 MPa stress for 10 minutes. The Fe-Ga-Al samples were annealed at 700°C and the Fe-Ga samples at 625°C. The magnetostriction was determined before and after stress annealing using compressive stresses of -0.7 MPa to -28 MPa for the Fe-Ga-Al samples and from ~0 to -97 MPa for the Fe-Ga samples. One of the stress annealed Fe_81.6Ga_18.4 samples was measured under tensile stresses up to 34 MPa. After annealing, all samples showed full performance at near-zero stresses and tensile stress up to +20 MPa.

This paper deals with fatigue behavior of paper-based friction materials under cyclic compression to tension loading and damage behavior under cyclic compressive loading. The fatigue tests under out-of-plane compressive stress to slight tensile stress loading are conducted to evaluate fatigue strength of friction materials. The tests under cyclic out-of-plane compressive loading are also conducted to investigate influence of compressive stress and load cycles on damage behavior. Two kinds of friction materials are composed of aramid-based fiber and phenolic resin, and cellulose fiber and phenolic resin. Their fatigue strengths decrease with increasing load cycles. The damage density in both materials increases with increasing compressive stress and load cycles.

Nano‐scale coherent twin boundaries (CTBs) significantly alter the mechanical and electrical properties of metallic materials. Despite a number of studies of the nanotwinned nanopillars in face‐centered cubic metals, investigations of them in body‐centered cubic (BCC) systems are rare. In this Letter, we explore the uniaxial deformation mechanisms of BCC tungsten nanopillars containing nano‐scale {112} CTBs using molecular dynamics (MD) simulations. Our work reveals a novel tension–compression asymmetric stress–strain response and deformation behavior, in conjunction with the effects of CTB spacing. With a relatively large CTB spacing, the plastic deformation in nanotwinned nanopillars is mainly controlled by dislocation nucleation from surface/CTB intersections, gliding on distant and adjacent slip planes under tensile and compressive loading, respectively; as a result, the tensile yield stress is almost invariant with respect to the CTB spacing, while the compressive yield stress increases with a decreasing CTB spacing. As the CTB spacing reduces to 1 nm, detwinning, exhibited by annihilation of {112} twin layers as a result of partial dislocations gliding on CTBs, is observed in both tension and compression; at higher strains, however, {111} incoherent twin boundaries, whose resistance to cracking contributes to strain hardening, are formed under tensile loading but not under compressive loading.

Infrared thermographic technique was employed for evaluating the temperature response in a Stainless steel grade 304 material subjected to different loading conditions such as monotonic tensile and compressive loading. In-situ temperature measurements were made from surface of the material by an infrared thermographic camera (JADE LWIR, Cedip Infrared Systems) while the material is being loaded. Cylindrical low cycle fatigue (LCF) samples were used in this study for monotonic tensile loading. Similarly, samples of aspect ratio 1.5 were used for analyzing monotonic compressive loading. As a material is subjected to tensile elastic loading, it undergoes cooling and when subjected to compressive loading, it undergoes heating. This phenomenon is called thermo-elastic effect. Based on our experimental observations, in case of monotonic tensile loading, the temperature of the material decreases till the material yields due to thermo-elastic effect and increases as the material plastically deforms, due to conversion of mechanical work done on the specimen into heat. But for the case of compressive loading, the temperature increases when the material is stressed in both cases of elastic as well as the elasto-plastic segment. This paper discusses the slope of the temperature response with respect to strain induced in the material and the effect of loading rate on the temperature measurements for the monotonic tensile and compressive loading. Comparison between the thermo-elastic slopes revealed that the thermo-elastic slope for the tensile loading is steeper than the slope from the compressive loading due to surface area contraction during the tensile loading and vice-versa. Experiments conducted at various loading rates ranging from 0.75 to 10 mm/min reveals that as the loading rate increases, temperature of the material increases.