Dynamic analysis of composite coil springs of arbitrary shape

The dynamic behavior of composite coil springs of arbitrary shape is investigated. The Timoshenko beam theory is adopted in the derivation of the governing equation. The material of the rod is assumed to be homogeneous, linear elastic and anisotropic. The effects of the ratio maximum diameter of the cylinder/thickness (D_max/d), the number of active turns (n), the helix pitch angle (α) and the ratio of the minimum to maximum cylinder radii (R_min/R_max) on the dynamic behavior of the composite barrel and hyperboloidal springs are investigated. The free and forced vibrations of composite coil springs of arbitrary shape such as barrel and hyperboloidal springs are analyzed through various examples.     

Low-energy charpy impact of interleaved CF/EP laminates

Carbon fiber (CF) reinforced epoxy (CF/EP) laminates laid up in different ways (cross-ply and quasi-isotropic) with and without various adhesive interlayers (A) were studied under three-point bending using instrumented low-energy impact at single and multiple bounces. Interleaves were a modified EP resin on polyester fabric, a modified EP resin, and a polyethersulphone (PES) film. The impact response depends strongly on whether the CFs are oriented longitudinally (L) or transversely (T) to the hammer edge in the outer bounced ply. The threshold incident energy (E _in,th) associated with severe damage to the laminates was much lower with the longitudinal outer ply.The impact fatigue response of the transverse cross-ply (TCP) and quasi-isotropic (TQI) composite beams showed that stiffness degradation starts at a certain a threshold number of impact (NOI) and follows a logarithmic decay as a function of NOI. This is in close analogy to fatigue tests under usual conditions. Deterioration in stiffness can be assigned to the relative change in the secant slope (E _max/x _max) of the load-displacement (F-x) traces. The related load-time (F-t) traces flatten due to impact fatigue so that their load maximum (F _max) shifts toward higher contact time.The efficiency of the interleaving was assessed in both single (atE _in,th3 J) and repeated impact (atE _in=1 J). The first technique allowed us to differentiate between the various interleaves, whereas the latter contributed to finding the optimum stacking and position of the interleaves.     

Low-energy tensile-impact behavior of superelastic NiTi shape memory alloy wires

Superelastic property of shape memory alloys (SMAs) is becoming increasingly important for impact applications due to their large recoverable strains and high capacity to dissipate energy. In this work, tensile behavior of superelastic NiTi SMA wires at impact strain rates was studied by instrumented tensile-impact technique, which allows to obtain material properties on the order of 1–10² s⁻¹. The results show that even at impact strain rates, martensite can be induced by tension in NiTi. At impact, a plateau stress appears during transformations similar to that at quasi-static strain rates, but 100–150 MPa higher in stress. This is due to the higher temperatures achieved during the deformation due to the close to adiabatic nature of the impact event. The influence of the strain rate over the mechanical behavior of NiTi was spread to the quasi-static strain rates so that the evolution of several parameters was also studied on the range 10⁻⁵–10² s⁻¹. Therefore, forward stress-induced martensitic (SIM) transformation stresses (σ^Ms and σ^Mf) and deformation energy (E_d) increase with strain rate, but they are strain rate independent from 10⁻¹ s⁻¹ at least until 10² s⁻¹. Reverse SIM transformation stresses (σ^As and σ^Af), recoverable strain energy (E_r), and dissipated energy (W_d) depend mainly on maximum strain achieved during the deformation, but for strains corresponding to a load–unload cycle with complete SIM transformation, σ^As, σ^Af and E_r are higher at impact than at quasi-static strain rates, and W_d shows similar values at very low strain rates and at impact.     

Fracture of knitted randomly oriented short-fiber composite

Fracture behavior of a chopped-mat E-glass fiber reinforced hybrid resin composite knitted with continuous poly(ethylene terephthalate) (PET) fibers is investigated by a combined experimental and analytical study. In both opening-mode (mode-I) and shear-mode (mode-II) fracture studies of the composite, the macroscopic critical stress intensities or toughnesses of the material are found to be distinct along the warp and fill directions of the knitting PET fibers. Values of K _IIc ( ^F ) and K _IIc ( ^F ) are lower than those of K _Ic ( ^W ), owing to different fracture mechanisms involved. In the mixed-mode fracture of the composite, a failure envelope in K _I and K _II is constructed. The different mechanisms involved in opening-mode, mode-II and mixed-mode fracture are studied with SEM observations.     

Monte Carlo method for simulating γ-ray interaction with materials: A case study on Si

In the present work, a Monte Carlo (MC) method has been developed to simulate various quantum mechanical processes for the energy loss of photons and fast electrons. The MC model is demonstrated by application to the interaction of photons with silicon over the energy range from 50 eV to 2 MeV and the subsequent electron cascades. The electron cascade process is commonly represented by two macroscopic parameters, the mean energy required to create an electron–hole pair, W, and the Fano factor, F, describing the electron yield and its variance. At energies lower than 5 keV, W generally decreases with increasing photon energy (from 3.96 to 3.58 eV), and it exhibits a sawtooth variation, as observed previously. However, discontinuities at the shell edges follow the photoionization cross-section, in contrast to previous results. The function, F(E_p), initially increases with increasing photon energy, E_p, to a maximum value of 0.187 around 155 eV, and then decreases at higher energies. Above the K shell edge, F has a value of 0.135. These results are consistent with experimental observations. The simulated distribution indicates that the interband transition and plasmon excitation are the most important mechanisms of electron–hole pair creation, while core shell ionization appears to be significant only at high energies.     

Relation between work of adhesion and work of fracture for simple interfaces

A study was conducted of the relation between work of adhesion and work of fracture for adhesive-substrate systems exhibiting fracture at the interface. Materials and test conditions were selected to eliminate contributions from irreversible, energy-consuming processes in the bulk of the adhesive or substrate. Values for W _a were determined from contact angle measurements made at room temperature with the adhesive in the liquid state; values for F were determined from inverted blister tests conducted at temperatures low enough for the adhesive to be in the solid state. The independent variable, W _a, ranged from about 40 mJ/m² to 144 mJ/m². The dependent variable, F, was found to range from 0.12 J/m² to 20 J/m², with most under 5 J/m². The excess of F over W _a was found to increase exponentially with W _a, and was proof of the occurrence of irreversible processes in specimens as they were loaded and fractured. The exponential behavior of (F – W _a) with W _a suggested that the irreversible process was orientation hardening. The absence of detectable permanent deformation of any kind in the bulk substrates or at the fracture surfaces, plus the incapability of the adhesives to sustain significant irreversible processes, led to the conclusion that the orientation hardening must have taken place in the substrate, within a thin layer (and small volume) adjacent to the interfacial plane.     

Mechanical properties of friction welded 6063 aluminum alloy and austenitic stainless steel

Friction welding of dissimilar metal combination of aluminum alloy and austenitic stainless steel was examined to investigate the effect of welding conditions on mechanical properties of the dissimilar metal combination. The welded joints were produced by varying forge pressure (F _g), friction pressure (F _r), and burn-off length (B). The joints were subjected to mechanical testing methods such as the tension, notch Charpy impact tests. The tensile strength and toughness decrease with an increase in friction pressure. The tensile strength decreases with an increase in burn-off length at a low forge pressure while tensile strength increases with an increase in burn-off length at a high forge pressure. The tensile failure of the welded joint occurred in aluminum alloy just away from interface in the thermo-mechanically affected zone indicates good joint strength at the condition of low friction pressure, high forge pressure, and high burn-off length. The maximum tensile strength was observed with low friction pressure and high forge pressure. The tensile strength of dissimilar joint is approximately equal to tensile strength of 6063 aluminum alloys at the condition of low friction pressure, high forge pressure, and high burn-off length. The tensile and impact failure of joints was examined under scanning electron microscope and failure modes were discussed.     

Microstructure and fracture behaviour of short and long fibre-reinforced polypropylene composites

Microstructure and fracture mechanical behaviour of injection-moulded, longer glass fibrereinforced polypropylene (Verton* aspect ratio 320) were studied as a function of fibre volume fraction and compared to that of shorter fibre-filled polypropylene (aspect ratio 70). Toughness was measured using instrumented notched lzod and falling weight impact tests, as well as compact tension specimens. It was found that the addition of longer fibres generally increased the toughness of the material, although more significant increases were seen in the impact tests than were seen in the compact tension test. For the latter results, a correlation between toughness improvement and microstructural details was performed on the basis of the microstructural efficiency concept, a semi-empirical approach of the formK _c,C = (a* +nR)K _c,M, where,K _c,C andK _c,M are the fracture toughnesses of the composite and the matrix, respectively,_a* is a matrix stress correction factor,n is a scaling parameter andR is a fibre reinforcement effectiveness factor. The latter corrects for differences in the composite microstructures, and incorporates effective fibre orientation factors, layering of injection moulded parts, and fibre volumes in the different layers.Nomenclature a crack length - a ^* matrix toughness correction factor - A cross-sectional area - B thickness of the sample plaques - C thickness of the composite core regions - E _peak energy adsorbed up to the maximum force in the impact load-displacement curve - E _t tensile modulus - F _max maximum force in impact force-displacement curves - f _p fibre orientation factor - f _pe effective orientation factor - f _pe,C effective orientation parameter, core region - f _{pe, s} effective orientation parameter, surface region - F critical load in the tensile test load-displacement curves - K _c critical stress intensity factor/fracture toughness - K _L fracture toughness of the composite materials - K _d dynamic fracture toughness - K _L fracture toughness of the matrix - L test with crack parallel to the mould filling direction - M microstructural efficiency factor - n scaling parameter for reinforcement effectiveness factor (energy absorbtion ratio) - R reinforcement effectiveness factor - S thickness of the composite surface regions - T test with crack perpendicular to the mould filling direction - V _f fibre volume fraction - V _m matrix volume fraction (= 1 —V _f) - W specimen width - W _f fibre weight fraction - W _m matrix weight fraction (= 1 —W _f) - X _n number average fibre length - X _v volume average fibre length - Y(a/ W) polynomial correction for compact tension specimens - variable in effective orientation factor formula - variable in effective orientation factor formula - _B strain to break - _c density of the composite - _f fibre density - _m matrix density - _F fracture strength - fibre angle with respect to a reference direction     

Thermal aging effects on mechanical and tribological performance of PEEK and short fiber reinforced PEEK composites

The effects of thermal aging on the properties of unfilled and random oriented short fiber reinforced PEEK and its composites have been studied. After the isothermal aging process, there is a remarkable decrease in degree of crystallinity but more organized crystallize structure achieved. As a result of transcrystalline layer formation, there was a considerable increase in the flexural modulus of materials. Thermal aging affects the impact properties of filled and unfilled PEEK dramatically. F_max, E_max and E · F_max results of both filled and unfilled aged PEEK and its composites are dramatically decreased. Thermal aging makes materials more brittle and there was a significant decrease in toughness. % Crystallinity is not the unique parameters to determine polymer’s performance. The orientation of crystals is another important parameter in microstructure and plays important role in mechanical and tribological properties of PEEK and its composites. There is a close relationship between thermal aging and microstructure. But there is not a linear relationship between microstructure and tribological properties. Microstructural changes after thermal aging serves developed mechanical properties. Increased mechanical properties results in improved tribological properties.     

Fabrication and Characterization of Cross-Connected Microchannel Porous Mesh Plates (CCMPMPs) by Multi-Cutter Milling

A new method for fabricating CCMPMPs, namely multi-cutter milling, is proposed and the fabrication principle is discussed. Then, a study of three microchannel parameters, the microchannel depth H_c, width W_c, and interval W_s, and two CCMPMP parameters, the porosity P and the total surface area per unit volume S_V, is presented. Furthermore, 3D FEM has been adopted to study the effective stress distribution, the metal flow velocity distribution, and the cutting forces. The results show that CCMPMPs can be successfully machined. H_c, W_c, and W_s can be controlled by the radial depth of cut a_e, the slotting cutter thickness E_t, and the gasket thickness E_g, while P and S_V can be changed by adjusting H_c, W_c, and W_s. Moreover, as a_e increases, the average resultant force increases, and the friction between chip and the side face of the machined microchannel, and between chip and the rake face, plays an increasingly important role in it.     

Arbitrarily Oriented Rounded Hole in a Linearly Elastic Plate

We deduce computational formulas for the initial angle of propagation of quasibrittle fracture and the ultimate uniform load applied to a homogeneous isotropic linearly elastic plane weakened by an arbitrarily oriented curvilinear rounded notch. By using the conditions of maximum of the quantities appearing in the proposed criterion, we establish, for the first time, the relationships between the parameters of this formula. For some special cases, these parameters can be found and the influence of curvature at the tip of the defect and various mechanisms of fracture of the plate can be clarified. We also studied the onset of fracture for cracks propagating according to the criteria of maximum tangential stresses _max, maximum specific energy of shaping W _f, and maximum specific total energy W.     

Lead-Free Relaxor Ferroelectric Ceramics with Ultrahigh Energy Storage Densities via Polymorphic Polar Nanoregions Design

One of the long-standing challenges of current lead-free energy storage ceramics for capacitors is how to improve their comprehensive energy storage properties effectively, that is, to achieve a synergistic improvement in the breakdown strength (E_b) and the difference between maximum polarization (P_max) and remnant polarization (P_r), making them comparable to those of lead-based capacitor materials. Here, a polymorphic polar nanoregions (PNRs) structural design by first introducing 0.06 mol BaTiO₃ into Bi_0.5Na_0.5TiO₃ is proposed to construct the morphotropic phase boundary with coexisting structures of micrometer-size domains and polymorphic nanodomains, enhance the electric field-induced polarization response (increase P_max). Then Sr(Al_0.5Ta_0.5)O₃ (SAT)-doped 0.94 Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (BNBT) energy storage ceramics with polymorphic PNRs structures are synthesized following the guidance of phase-field simulation and rational composition design (decrease P_r). Finally, a large recoverable energy density (W_rec) of 8.33 J cm⁻³ and a high energy efficiency (η) of 90.8% under 555 kV cm⁻¹ are obtained in the 0.85BNBT-0.15SAT ceramic prepared by repeated rolling process method (enhance E_b), superior to most practical lead-free competitors increased consideration of the stability of temperature (a variation <±6.2%) and frequency (W_rec > 5.0  cm⁻³, η > 90%) at 400 kV cm⁻¹. This strategy provides a new conception for the design of other-based multifunctional energy storage dielectrics.     

Ultrasonic Velocity Studies of Drug Parvon-spas in Mixed Alcohol–Water Solvent Systems at 25°C

Ultrasonic velocities and densities of the drug Parvon-spas in binary mixtures of water with methanol (MeOH), ethanol (EtOH), and propan-1-ol (1-PrOH) have been measured over the complete solvent composition range at 10 mol% intervals at 25°C. Various acoustic parameters such as the acoustic impedance (Z), adiabatic compressibility (β), intermolecular free length (L_f), relative association (R.A.), molar volume (V_m), and molar sound velocity (R_m) have been calculated. In addition, excess functions, i.e., excess adiabatic compressibility (β^E), excess intermolecular free length (L_f^E), excess molar volume (V^E), excess ultrasonic velocity (U^E), and excess acoustic impedance (Z^E) for these three solvent mixtures in the absence and presence of the drug have been calculated. A different behavior of these parameters in these alcohol systems has been discussed in terms of the length of the alcohol molecule, the molecular volume, as well as inter/intramolecular interactions of these molecules.     

Substrate dependent cracking behavior of CrAlN coatings

The present study investigated the effect of substrate deformation behavior on crack resistance of CrAlN coatings under quasi-static and cyclic loads using nanoindentation. (Cr₄₇Al₅₃)N coatings were deposited on cemented carbide WC-Co and high-speed steel HS652C substrates through physical vapor deposition (PVD) und characterized. In order to study the coating cracking behavior, the coated substrates were subjected to quasi-static nanoindentations with indentation force F_max = 1 N, F_max = 1.5 N and F_max = 2 N. Moreover, the crack resistance under cyclic loading with frequency f = 0.16 Hz was analyzed at F = 1 N and F = 1.5 N after n = 900 cycles. A conical diamond indenter was used for the tests. At the end, the indentation imprints were analyzed by scanning electron microscopy (SEM). The substrate dependency was apparent in cracking behavior of the coating. Albeit the lower indentation depth compared to the variant with HS6-5-2C substrate, the CrAlN coating on WC-Co substrate showed surface cracks under quasi-static and cyclic loading. These cracks on the coated surface were absent in the variant with HS6-5-2C substrate. This could be related to higher resistance of cemented carbide substrates against plastic deformation, prompting earlier crack initiation in CrAlN coating for effective energy dissipation during indentation.     

Magneto-Peltier cooling of single-crystal Bi<Subscript>1-<Emphasis Type="Italic">X</Emphasis></Subscript>Sb<Subscript><Emphasis Type="Italic">X</Emphasis></Subscript> (<Emphasis Type="Italic">X </Emphasis>= 0.12 and 0.15) alloys

The cooling temperatures of rectangular parallelepiped Bi_1-X Sb _X (X = 0.12 and 0.15) single-crystals with the same thickness of t = 2 mm but different width W were measured at 113 K and 290 K as a function of electric current in the magnetic field B up to 2.17 T. The magnetic field was aligned along the thickness t of a sample and the current flows along its length L through the copper leads soldered to both end surfaces of cross section (W × t), where W, t and L are parallel to the binary, bisector and trigonal axes of the single-crystal, respectively. The thermoelement was not in contact with a heat sink. The cooling temperature of Bi_0.85Sb_0.15 at 290 K was increased with an increase of B and was almost symmetric for the reverse of the field direction, while at 113 K it exhibited a maximum at B = ±0.25 T and a strong asymmetry for the field direction. The largest maximum cooling temperature ΔT _max of Bi_0.85Sb_0.15 was achieved when a thermoelement has optimum dimensions so that heat energy is hardly generated at the cold side. When the single-crystal Bi_0.85Sb_0.15 alloy has optimum dimensions of L = 15 mm, W = 4 mm and t = 2 mm, the ΔT _max at 290 K increased from 4.2 K in B = 0 T to 9.6 K in B = +2.17 T, so that it exceeded ΔT _max values of 5.7 K obtained for a typical Bi₂Te₃ and 8.5 K measured previously for Bi single-crystal in B = +2.17 T.     

MEASUREMENT OF STRETCH ZONE HEIGHT AND ITS RELATIONSHIP TO CRACK TIP OPENING DISPLACEMENT AND INITIATION J-VALUE IN AN AISI 316 STAINLESS STEEL

An accurate method using SEM for the measurement of stretch zone height (SZH) on fracture surfaces has been established. This method does not make any assumption regarding crack blunting angle θ, and for 316 stainless steel in the present investigation θ was in the range of 50 to 67°, contrary to the common assumption of 45°. The semi-empirical equations, SZH(T) = 2.5 SZW (stretch zone width) and SZW = 89(J/E), reported in the literature were found to give very conservative predictions of initiation toughness J_i for an AISI 316 stainless steel. Lowerbound values of the coefficient m in the equation, J = mσ_yδ, relating J to CTOD, δ, is found to be 1.5–1.7 for the 316 SS used in this investigation; the upperbound value for m is found to be 2.6. The plastic CTOD values (δ_max) corresponding to the maximum load-point on the instrumented impact test traces are not sensitive to the aging conditions and as they incorporate significant crack growth effects they cannot be used for predicting J_i, by a procedure similar to that discussed above. The ratio t₁/t_T, where t_i is the time to crack initiation and t_i is the time to total fracture, in precracked Charpy tests of unaged and aged 316 SS used in this investigation (a/W=0.55 to 0.8) corresponds to 0.15 to 0.17.     

Conflict between internal combustion engine and thermoelectric generator during waste heat recovery in cars

It is shown that an internal combustion engine and a thermoelectric generator (TEG) arranged on the exhaust pipe of this engine come into the conflict of thermal machines that is related to using the same energy resource. The conflict grows with increasing useful electric power W _e of the TEG, which leads to the limitation of both the maximum TEG output power (W _e^max) and the possibility of waste heat recovery in cars.     

In vitro–in vivo extrapolation (IVIVE) for predicting human intestinal absorption and first-pass elimination of drugs: principles and applications

Oral administration remains the preferred dosing method in clinical practice and drug development. Oral bioavailability (F) is a function of the fraction absorbed (F_abs), gastrointestinal or gut wall availability (F_G), and hepatic availability (F_H). Therefore, predicting intestinal absorption (F_abs) and first-pass elimination (F_G and F_H) from in vitro data may facilitate the selection of more orally bioavailable drug candidates in earlier stages of drug discovery and development. This review provides an overview of the determinants of intestinal absorption and first-pass elimination of drugs and focuses on the principles and applications of conventional in vitro--in vivo extrapolation (IVIVE) methods to predict F_abs, F_G, and F_H in humans.     

Revealing the Cooperative Relationship between Spin,Energy, and Polarization Parameters toward Developing High‐Efficiency Exciplex Light‐Emitting Diodes

Experimental studies to reveal the cooperative relationship between spin, energy, and polarization through intermolecular charge‐transfer dipoles to harvest nonradiative triplets into radiative singlets in exciplex light‐emitting diodes are reported. Magneto‐photoluminescence studies reveal that the triplet‐to‐singlet conversion in exciplexes involves an artificially generated spin‐orbital coupling (SOC). The photoinduced electron parametric resonance measurements indicate that the intermolecular charge‐transfer occurs with forming electric dipoles (D^+?→A^??), providing the ionic polarization to generate SOC in exciplexes. By having different singlet‐triplet energy differences (ΔE_ST) in 9,9′‐diphenyl‐9H,9′H‐3,3′‐bicarbazole (BCzPh):3′,3′″,3′″″‐(1,3,5‐triazine‐2,4,6‐triyl)tris(([1,1′‐biphenyl]‐3‐carbonitrile)) (CN‐T2T) (ΔE_ST = 30 meV) and BCzPh:bis‐4,6‐(3,5‐di‐3‐pyridylphenyl)‐2‐methyl‐pyrimidine (B3PYMPM) (ΔE_ST = 130 meV) exciplexes, the SOC generated by the intermolecular charge‐transfer states shows large and small values (reflected by different internal magnetic parameters: 274 vs 17 mT) with high and low external quantum efficiency maximum, EQE_max (21.05% vs 4.89%), respectively. To further explore the cooperative relationship of spin, energy, and polarization parameters, different photoluminescence wavelengths are selected to concurrently change SOC, ΔE_ST, and polarization while monitoring delayed fluorescence. When the electron clouds become more deformed at a longer emitting wavelength due to reduced dipole (D^+?→A^??) size, enhanced SOC, increased orbital polarization, and decreased ΔE_ST can simultaneously occur to cooperatively operate the triplet‐to‐singlet conversion.     

Existence and construction of translation models for stationary non-Gaussian processes

Translation models are memoryless transformations of Gaussian processes specified by their marginal distribution F and covariance function ξ. Iteration schemes are commonly used to find probability laws of Gaussian images of translation models, although these schemes may not converge since translation models do not exist for arbitrary functions F and ξ. Pairs (F,ξ) for which translation models exist are said to be consistent. Optimization algorithms are developed for constructing translation models that, for consistent pairs (F,ξ), match F and ξ, and, for inconsistent pairs (F,ξ), match F or ξ and approximate ξ or F. The resulting translation models can be used in Monte Carlo simulation studies.