Instantaneous Strength Research Articles

Some aspects on plastic deformation of copper and copper–titanium carbide powder metallurgy composite preforms during cold upsetting

The densification, workability and strain hardening behaviour of sintered copper and Cu–7.5%TiC powder metallurgy (P/M) composite preforms during cold upsetting were investigated by the constitutive model using the experimental data. Cold upsetting of copper and Cu–7.5% TiC composite preforms having different aspect ratios were carried out and the formability behaviour of the preforms under triaxial stress state was determined. The mechanisms most likely involved in the constitutive model, namely, densification and strain hardening were studied. The effects of aspect ratio and addition of titanium carbide to copper on the formability behaviour and various constants involved in the constitutive model, namely, instantaneous density coefficient, instantaneous strain hardening index, instantaneous strain rate sensitivity and instantaneous strength coefficient were discussed in detail.

Effect of carbon content on instantaneous strain-hardening behaviour of powder metallurgy steels

Complete experimental investigation on the instantaneous strain-hardening behaviour of powder metallurgy preforms of pure iron and steels containing 0.4% and 0.8% carbon were carried out. The above-mentioned powder metallurgy sintered preforms with two different aspect ratios namely 0.39 and 0.59 were cold upset with graphite as lubricant and their strain-hardening behaviour under triaxial stress state condition was evaluated. For all the above-said preforms the stress–strain relationship was established, instantaneous strain hardening index was determined and its variation with respect to the axial strain and the relative density were plotted, studied and discussed relative to their as-sintered microstructures. Also the characteristics of the instantaneous strength coefficient with respect to the relative density was analyzed and presented.

Effect of geometric work-hardening and matrix work-hardening on new constitutive relationship for aluminium–alumina P/M composite during cold upsetting

The densification and strain hardening behaviour during cold deformation of sintered aluminum–3.5% alumina powder metallurgy preforms were investigated by constitutive model and experimental data obtained with no and with subsequent annealing. The mechanisms most likely involved in the constitutive model, namely, densification and strain hardening were studied. The effect of geometric and matrix work hardening on the various constants involved in the constitutive model, namely, instantaneous density coefficient, instantaneous strain hardening index, instantaneous strain rate sensitivity and instantaneous strength coefficient were discussed in detail.

Large deformation and fracture mechanics of a beta-helical protein nanotube: Atomistic and continuum modeling

We report molecular dynamics (MD) simulation and atomistically informed continuum modeling of the nanomechanics of the β-helix protein motif, a key building block of amyloids associated with Alzheimer’s, Huntington’s and prion diseases, forming a nanotube-like protein structure. We find that the β-helix structure is extremely extensible and can sustain tensile deformation up to 800% engineering strain without rupture of the covalently bonded protein backbone. Our atomistic simulation results reveal that the instantaneous strength of the tube is proportional to the rate of H-bond rupture, providing a link between the dynamics of hydrogen bond rupture and the mechanical signature of the protein structure. This finding proves that concurrent as opposed to sequential breaking of bonds leads to higher mechanical resistance, corroborating earlier results found in studies of β-sheet protein domains. Inspired by the beta-helical domain of the needle-like cell puncture device of bacteriophage T4, we carry out compressive loading simulations of the β-helix, and show that this protein motif can withstand extremely large compressive loads, far exceeding the tensile strength. Different mechanical deformation modes under compressive loading are summarized in a deformation map. Our findings illustrate the potential of the β-helix protein motif as an inspiration for nano-scale materials applications, ranging from stiff nanotubes to self-assembling peptide based fibers inspired by amyloids.

Numerical simulation of rheological processes in hardening plastics under stress control

The paper concerns the simulation of rheological processes in hardening plastics (resins) under stress control. It is assumed that the resins work in the glassy state, under normal conditions, and the rheological processes are quasi-static and isothermal. The reduced stress levels do not exceed 30% of the instantaneous tensile strength. A resin is modelled as a homogeneous, isotropic, linearly viscoelastic material. The HWKK/H rheological model, developed recently by the author, is used. Short-term, medium-term, and long-term shear strain components are considered and described by one fractional and two normal exponential functions as the stress history (memory) functions. A novel algorithm for the numerical simulation of rheological processes in resins has been developed, which is unified for all stress history functions in the HWKK/H model. The algorithm employs the Boltzmann superposition principle, a virtual table for the classic creep process, and a high-rank Gaussian quadrature. The stress function is approximated with a stair case function. The constitutive equations governing the HWKK/H model are trans formed into an algebraic form suitable for algorithmization. The problem of quasi-exact calculation of the double-improper integral resulting from the fractional exponential function is solved effectively. The algorithm has been tested successfully on selected loading programs of unidirectional tension of epoxide.

An experimental investigation on work hardening behaviour of elliptical shaped billets of aluminium during cold upsetting

The present investigation has been undertaken to evaluate the work hardening phenomenon experienced in elliptical shaped billets of commercially pure aluminium during axial compression tests using graphite mixed with oil as lubricant on both sides. It is very essential to study the plastic deformation of any material and also is an important parameter used to describe the work hardening characteristics of materials. The parameters namely the instantaneous strain hardening exponent ( n i) and the instantaneous strength coefficient ( k i) were evaluated during the cold upsetting of commercially pure aluminium under various stress state conditions namely the uniaxial, the plane and the triaxial. Samples with three different aspect ratios (ratio of height to diameter), namely, 0.5, 0.75 and 1.0 and five different b/ a ratios (ratio of minor diameter to major diameter) of 0.6, 0.7, 0.8, 0.9 and 1.0 were prepared and cold upset forged. The strain hardening exponent ( n i) and the strength coefficient ( k i) were obtained for each aspect ratios. It has been observed that the value of strain hardening exponent ( n i) varies very much and found to be different for different aspect ratios of the billets tested. Further the value of the strength coefficient ( k i) is found to be increasing for different aspect ratios under different stress state conditions.

The Timing of Perceptual Decisions for Ambiguous Face Stimuli in the Human Ventral Visual Cortex

When observers must discriminate a weak sensory signal in noise, early sensory areas seem to reflect the instantaneous strength of the sensory signal. In contrast, high-level parietal and prefrontal areas appear to integrate these signals over time with activity peaking at the time of the observer's decision. Here, we used functional magnetic resonance imaging to investigate how the brain forms perceptual decisions about complex visual forms in a challenging task, requiring the discrimination of ambiguous 2-tone Mooney faces and visually similar nonface images. Face-selective areas in the ventral visual cortex showed greater activity when subjects reported perceiving a face as compared with a nonface, even on error trials. More important, activity was closely related to the time of the subject's decision for face judgments, even on individual trials, and resembled the time course of activity in motor cortex corresponding to the subject's behavioral report. These results indicate that perceptual decisions about ambiguous face-like stimuli are reflected early in the sensorimotor pathway, in face-selective regions of the ventral visual cortex. Activity in these areas may represent a potential rate-limiting step in the pathway from sensation to action when subjects must reach a decision about ambiguous face-like stimuli.

Phenomenon of instantaneous strain hardening behaviour of sintered Al–Fe composite preforms during cold axial forming

Cold upsetting experiments were carried out on sintered Al–Fe composite preforms in order to evaluate their work-hardening characteristics. Preforms of 92% of theoretical density, with two initial aspect ratios were prepared using a suitable die-set assembly on a 0.6 MN capacity hydraulic press. Sintering was carried out in an electric muffle furnace for a period of 1 h at 520 °C. Each sintered compact was subjected to incremental compressive loading after each step of deformation. The instantaneous strain-hardening exponent instantaneous strain-hardening exponent ( n i) and strength coefficient instantaneous strength coefficient ( k i) of the Al–Fe composite preforms were calculated and found to be reached the peak value when the deformation or packing density is at low value. Further, it has been observed that the value of n i and k i decreased and found to be constant It has further been established that the iron particle-size of the preforms played a predominant role in influencing both n i and k i.

An experimental investigation on strain hardening behaviour of aluminium – 3.5% alumina powder metallurgy composite preform under various stress states during cold upset forming

An experimental investigation on instantaneous strain hardening behaviour of aluminium – 3.5% alumina powder metallurgy composite preforms for three different stress state conditions, namely, the uniaxial, the plane and the triaxial has been carried out. Sintered aluminium–alumina composite with three different aspect ratios (height to diameter ratio), namely, 0.35, 0.56 and 0.72 and two different initial preform relative densities of 0.80 and 0.90 were prepared, sintered at 550 ± 10 °C under the cover of protective indigenously developed ceramic coating for a period of 90 min in an electric muffle furnace and cooled inside the furnace itself. Sintered but mildly machined disc specimens were cold deformed under axial tests using mirror polished flat dies. The instantaneous strain hardening exponent ( n i ) and the instantaneous strength coefficient ( K i ) were determined for each aspect ratios for all three different stress state conditions and the results were analyzed in the present work. The analysis of the experimental results has shown that the instantaneous strain hardening exponent ( n i ) and the strength coefficient ( K i ) are greater for the triaxial stress state condition irrespective of the initial preform densities and the aspect ratios when compared to uniaxial and plane stress state conditions.

Mechanical property of induction brazing TiAl-based intermetallics to steel 35CrMo using AgCuTi filler metal

TiAl-based intermetallics joined by vacuum induction brazing using Ag–Cu35.2–Ti1.8 filler alloy at 850–970 °C for 1–10 min was investigated. The optimum brazing parameters are as follows: brazing temperature is 870–880 °C, brazing time is 4–6 min. The maximum tensile strength of the joint is 320 MPa for the specimen induction brazed at for 870 °C for 5 min, and at this time, the thickness of Al–Cu–Ti intermetallic compound layer is about one third of that of the whole interface. Interfacial microstructure of TiAl/Ag–Cu–Ti/35CrMo joint brazed at 870 °C for 5 min is instable at 400 °C. The instantaneous high temperature strength is 248 MPa at 400 °C, the fracture location of joint is mainly at Al–Cu–Ti intermetallic compound layer, the fracture pattern of brazed joint deviate from transcrystalline crack at room temperature into intergranular crack.

Lower extremity skeletal muscle function in persons with incomplete spinal cord injury

A cross-sectional study design. To characterize and specifically quantify impairments in muscle function after chronic incomplete spinal cord injury (SCI). University of Florida, Gainesville, FL, USA. Voluntary and electrically elicited contractile measurements were performed and voluntary activation deficits were quantitatively determined in the knee extensor and ankle plantar flexor muscle groups in 10 individuals with chronic incomplete SCI (C5-T8, ASIA C or D) and age-, gender-, height- and body weight matched healthy controls. Persons with incomplete-SCI were able to produce only 36 and 24% of the knee extensor torque and 38 and 26% of the plantar flexor torque generated by noninjured controls in the self-reported less-involved and more-involved limbs, respectively (P<0.05). In addition, both indices of explosive or instantaneous muscle strength, torque200 (absolute torque reached at 200 ms) and the average rate of torque development (ARTD) were dramatically reduced in the ankle plantar flexor and knee extensor muscle groups in persons with incomplete-SCI. However, the deficit in instantaneous muscle strength was most pronounced in the ankle plantar flexor muscles, with an 11.7-fold difference between the torque200 measured in the self-reported more involved limb and a 5-fold difference in the less-involved limb compared to control muscles. Voluntary activation deficits ranged between 42 and 66% in both muscle groups. Interestingly, electrically elicited contractile properties did not differ between the groups. The resultant impact of incomplete-SCI is that affected muscles not only become weak, but slow to develop voluntary torque. We speculate that the large deficit in torque200 and ARTD in the ankle plantar flexors muscles of persons with incomplete-SCI may limit locomotor function. The results presented in this study provide a quantitative and sensitive assessment of muscle function upon which future research examining rehabilitation programs aimed at restoring muscle function and promoting functional recovery after incomplete-SCI may be based.

Modelling the effect of particle size and iron content on forming of Al–Fe composite preforms using neural network

Cold upsetting experiments were carried out on sintered Al–Fe composite preforms inorder to model and analyse the formability by simulation using neural network (NN). A model has been developed with a radial basis NN algorithm. The data used were collected by the experimental set up in the laboratory for the sintered Al–Fe composites with the various preform densities, the particle sizes and the aspect ratios. The network is trained to predict the forming characteristics such as the axial stress, the hoop stress, the hydrostatic stress and the Poisson ratio. In addition to that, the value of strain hardening coefficients such as instantaneous strength coefficient ( k i) and instantaneous strain hardening exponent ( n i) is also simulated to find the effect of particle size and the percent of iron content on formability. Regression analysis has confirmed a good agreement between the predicted and the experimental data with least error and hence this approach helps to facilitate a knowledge base in order to generate advice for the designer at the earlier stages of design so that concurrent engineering practices can be made.

On the indirect electro-optic modulation in noncentrosymmetric uniaxial crystals

In electro-optic crystals the dependence of directions of refracted waves and rays on the instantaneous strength of the modulating field may change the following parameters: polarization azimuths, distances covered by the divergent fast and slow waves, refractive indices, effective electro-optic coefficients, and also the extent of overlap of the partially interfering light beams. Despite the fact that in noncentrosymmetric crystals the changes may be due to the linear electro-optic effect, the dependences, when appearing simultaneously, for some directions of the light and modulating field can result in a complex indirect modulation observed on higher harmonics of the electric field. Taking as an example the LiNbO3 crystal, the indirect modulation on the second harmonic is investigated employing the Jones matrix calculus.

An investigation on instantaneous strain hardening behaviour in three dimensions of aluminium–iron composites during cold upsetting

Strain hardening of a material is an important phenomenon, which is required to study the plastic deformation of any material and also is an important parameter in the study of workability criteria of metals. The present investigation has been undertaken to evaluate the instantaneous strain hardening behaviour experienced during the cold working of sintered aluminium iron composites with various iron contents from 0 to 10% under various stress state conditions namely uniaxial, plane and triaxial. Sintered preforms with two different aspect ratios namely 0.44 and 0.75 with for different per cent of iron contents ranging from 0 to 10% were prepared and cold forged. The instantaneous strain hardening exponent ( n i) and the instantaneous strength coefficient ( K i) were obtained for each aspect ratios and iron contents and found that they have showed tremendous variations in the instantaneous values of strain hardening exponent and strength coefficient for the addition of different iron content, for different aspect ratios and for different stress state conditions.

Rheological properties and structural changes in different sections of boiled abalone meat

Changes in tissue structures, rheological properties of cross- and vertical section boiled abalone meat were studied in relation to boiling time. The adductor muscle of abalone Haliotis discus which was removed from the shell, was boiled for 1, 2, and 3 h, respectively. Then it was cut up and separated into cross- and vertical section meat. When observed by a light microscope and a scanning electron microscope, structural changes in the myofibrils were greatest in the cross section meat compared with the vertical section meat. When boiling time was increased from 1 h to 3 h, the instantaneous modulus E 0 and rupture strength of both section meat decreased gradually with increased boiling time, and no significant differences were observed between these two section meat for the same boiling time. When boiled for 1 h, the relaxation time of cross section meat was much longer than that of vertical section meat. There were no significant changes in the relaxation time of vertical section for different boiling time, but the relaxation time of cross section meat was reduced gradually with increasing boiling time. These results confirmed that the difference in rheological properties between the cross- and vertical section meat was mainly due to the denaturation level of myofibrils when heated for 1 h, as well as due to the changes in the amount of denatured proteins, and the manner in which the inner denatured protein components were exchanged after boiling time was increased from 1 h to 3 h.

Office hours pulsed brachytherapy boost in breast cancer

Background and purpose: Radiobiological studies suggest equivalent biological effects between continuous low dose rate brachytherapy (CLDR) and pulsed brachytherapy (PB) when pulses are applied without interruption every hour. However, radiation protection and institute-specific demands requested the design of a practical PB protocol substituting the CLDR boost in breast cancer patients. An office hours scheme was designed, considering the CLDR dose rate, the overall treatment time, pulse frequency and tissue repair characteristics. Radiobiological details are presented as well as the logistics and technical feasibility of the scheme after treatment of the first 100 patients.Materials and methods: Biologically effective doses (BEDs) were calculated according to the linear quadratic model for incomplete repair. Radiobiological parameters included an α/β value of 3 Gy for normal tissue late effects and 10 Gy for early normal tissue or tumour effects. Tissue repair half-time ranged from 0.1 to 6 h. The reference CLDR dose rate of 0.80 Gy/h was obtained retrospectively from analysis of patients' data. The treatment procedure was evaluated with regard to variations in implant characteristics after treatment of 100 patients.Results: A PB protocol was designed consisting of two treatment blocks separated by a night break. Dose delivery in PB was 20 Gy in two 10 Gy blocks and, for application of the 15 Gy boost, one 10 Gy block plus one 5 Gy block. The dose per pulse was 1.67 Gy, applied with a period time of approximately 1.5 h. An inter-patient variation of 30% (1 SD) was observed in the instantaneous source strength. Taking also the spread in implant size into account, the net variation in pulse duration amounted to 38%.Conclusion: An office hours PB boost regimen was designed for substitution of the CLDR boost in breast-conserving therapy on the basis of the BED. First treatment experience shows the office hour regimen to be convenient to the patients and no technical perturbations were encountered.

Instantaneous target strength measurement of live squid with synchronized video image

The TS is a complex function of the fish’s size, shape, orientation, behavior, and internal structure, as well as of the acoustic wavelength employed. Therefore, for practical purposes, it is necessary to measure the TS experimentally. There is a considerable amount of knowledge about the TS of fish. Information about the TS of squid, however, is much less. Through previous studies over the past 6 years at our experimental field, acoustic equipment has been modified and gradually stabilized. It was also possible to use live squid in our specially designed experimental barge equipped with two underwater video cameras which look at the side view and upward. Preliminary TS and orientation measurements were done on single tethered live squid Todarodes pacificus. The live squid was suspended with monofilament nylon string near the acoustic beam axis and positioned 3.5 m below the transducers. The echo signals of the squid at six frequencies were converted to amplitude modulated signals in audible frequency, then they were recorded on audio channels of video tape with a video image simultaneously. Afterward, the echo envelopes were demodulated to analyze the relationship between TS and the swimming aspect of live squid by synchronized video image. Preliminary results from this measurement will be presented.

Statistical theory as applied to cyclic hardening

Monotonic and cyclic stressing are compared on the basis of the statistical theory of flow and strain hardening. The parameters describing yield and strain hardening are shown to be very similar in both cases of stressing. For example, the hardening parameter of cyclic stressing as a function of the instantaneous yield strength reveals a four-stage strain hardening similar to that in monotonic stressing. The results support the idea that the basic factors controlling yielding and strain hardening are more or less the same independent of the mode how the stressing is done.

Structural response analysis of the confinement system of the Ignalina nuclear power plant

Presented is a study of the accident confinement system of the Ignalina nuclear power plant (NPP) with Russian acronym for ‘channelled large power reactor’ (RBMK)-1500 reactors for the ultimate design basis accident. The computation techniques described pertain to the strength analysis of the accident confinement system (ACS): the design of the ACS compartments, materials, and manner of reinforcement. In strength predictions of reinforced concrete to evaluate the carrying-ability of the structure and its performance by the technique of limit analysis. The ACS analysis with finite elements (FE) of several types yielded instantaneous reserve strength factors for static loads. Numerical results of dynamic effects to the strength evaluation for compartment which houses the downcomers of drum separators are presented. The behaviour of pressure and temperature were taken from the results of thermal hydraulics models. Because of the relatively slow rate of loading, the investigation has confirmed that dynamic effects do not contribute additional insight to regular static analysis.

Discriminating Between Onlap and Lithologic Interfingering in Seismic Models of Outcrops

Seismic models of outcrops have shown that near the limits of resolution the seismic reflection tool records rapid facies changes as false lap-outs. We examined one such outcrop, the Triassic platform flank of Picco di Vallandro (Durrenstein) in northern Italy, to develop criteria for recognizing false lap-out patterns. Using measured sections, photo mosaics of the continuous outcrop, and petrophysical measurements on samples, two contrasting impedance models were constructed. One model, supported by field observation, shows interfingering between basin marls and slope carbonates. The second model shows onlap of basin marls against slope carbonates, but with similar overall geometries to the first model. Vertical incidence seismic models were produced at frequencies between 50 and 150 Hz and with displays of seismic amplitude, as well as two seismic attributes-instantaneous phase and reflection strength. At 50 Hz, the two lithologic models are seismically indistinguishable, both showing onlap of basin units onto the slope. At 90 Hz, displays of instantaneous phase begin to reveal the stratigraphic interfingering, whereas seismic amplitude displays require frequencies of 150 Hz to do so. Reflection strength accurately portrays the distribution of the two major facies in the entire range of examined frequencies, but does not show sufficient detail to reveal interfingering vs. onlap. The same trends were visible with finite difference modeling of the full waveform. Here, the differences between interfingering and onlap become visible at 150 Hz in the phase model, where seismic amplitude displays at this frequency are still ambiguous. The phase model, however, fails to differentiate between slope dip and the basin sediment wedge, whereas this wedge is clearly mapped by the reflection strength. A combination of instantaneous phase and reflection strength provides a decisive advantage over conventional amplitude displays in recognizing rapid facies changes in seismic reflection data.