Fracture Characteristics of Fatigue Failure of a Vehicle’s Ductile Iron Steering Knuckle

The steering knuckle, being a part of the vehicle’s steering and suspension system, undergoes time-varying loading during its service life. Since it is connected to the steering parts and strut assembly from one side and the wheel hub assembly from the other, it has complex restraint and constraint conditions and tolerates a combination of loads. In addition, parameters such as internal defects, stress concentrations and gradients, surface finish, and residual stresses can have considerable influence while designing for fatigue. A vehicle with a 2.500 cm³ (2.5 L) volume engine was being driven during a rainy day in a congested road at a speed of about 10 km/h, when suddenly the vehicle lost its orientation and crushed over a parked vehicle on the right side of the road without any human injury. The driver insisted that he heard an intense noise of a metal undergoing rupture from the front right side of the vehicle’s suspension system and immediately lost control of the vehicle. The producing company of the vehicle on the other hand, after on-site visual inspection, came to the conclusion that due to the driver’s error the vehicle turned to the right and as a consequence of the crash the steering knuckle was broken into two parts. Failure analysis conducted as presented in this article reveals the mechanism of fracture mainly due to bending fatigue.     

Über den Einfluß der Kornverteilungskurve auf das dynamische und das kumulative Verhalten nichtbindiger Böden

On the influence of the grain size distribution curve on the dynamic and the cumulative behaviour of non-cohesive soils. This paper presents experimental studies on non-cohesive soils on the influence of the grain size distribution curve on the dynamic soil properties and the accumulation of residual deformations under cyclic loading. It is shown that the dynamic shear modulus is not influenced by the mean grain diameter but decreases strongly with the non-uniformity. For a non-uniform soil the common empirical formulas overestimate the dynamic shear modulus by up to 70%. Also the residual deformations under cyclic loading depend significantly on the grain size distribution curve. They are larger for fine-grained soils. Under cyclic loading non-uniform soils densify much faster than uniform soils.     

Comparison of Gas and Liquid Propylene Polymerization Technique – Hydrogen Effect on Thermal,Rheological, and Morphological Properties of PP

Summary: A comparison of PP qualities, which are produced with two different polymerization techniques–gas phase(GP) and liquid pool (LP)–under precise control of the polymerization temperature (70 °C) and pressure (GP = 25 bar, LP < 60 bar) using identical Ziegler‐Natta catalyst (TiCl₄/phthalate/MgCl₂ + TEA/silane), is presented. A series of homopolymer PP in a wide MW range from 100 000 to 1 600 000 g · mol^?1 was polymerized. During polymerization all samples were characterized exactly by their Rp‐profil. The effect of hydrogen on the initial reaction rate and on MW and MWD was analyzed on the basis of this so‐called kinetic fingerprint. The results showed that the polymerization rate reached a maximum for LP, of about 150 kg · g_cat^?1 · h^?1, in contrast to GP with a maximum of R_p,₀ = 45 kg · g_cat^?1 · h^?1. Analysis was carried out by means of GPC, SEM, DSC, platte‐platte rheometer, and WAXS. The results first showed that the MWD of LP PP is narrower (PD ～ 6.8) than for the GP PP (PD ～ 8), polymerized in two steps. An SEM study of the powder particle shows the typical dent surface morphology of polymers using Ziegler‐Natta catalysts for polymerization. WAXS and DSC analysis demonstrated that almost only the α‐modification of crystalline structure exists and that the crystallinity becomes considerably higher after solidification from melt. Furthermore, it was found that the crystallite size distribution depends on the polymerization technique. Rheological studies indicate that GP PP behaves more elastically. To summarize, it is shown that PP produced with the LP polymerization technique is more homogenous and of high quality.

Particle geometry of gas phase and liquid pool polymerized PP powder observed by SEM (PP‐L0).     

Fire hazard of compressed straw as an insulation material for wooden structures

The construction sector continues to adapt to the challenges posed by climate change. Architects and engineers aim to build sustainable, energy, resource, and cost-efficient structures by increasingly using bio-based building materials. However, fire safety has always been a significant concern for timber building construction internationally. The objective of the study presented in this article is to document fire hazards of compressed straw when used as thermal and acoustic insulation within wood-framed building assemblies. Three densities of compressed straw (75, 125, and 175 kg/m³) were selected and their combustion and thermal responses were evaluated at various scales, in attempt to define the optimal density considering various factors. The performance of the straw was also compared with commercially available insulation materials and then tested under exposure to severe heating in medium-scale wood-framed assemblies to evaluate the impacts of the straw as compared with a noncombustible insulation. The compressed straw with a density of 75 kg/m³ was found to have the best behavior with respect to both reactions to fire and insulation properties. The results suggest that compressed may have similar or better behavior under the heating conditions investigated when compared to a commercially available combustible insulation material. The use of this material as a primary insulation in a buildings is considered manageable by thoughtful design, construction, and building use without unduly increasing risks associated with fire.     

Material characterization and bioactivity evaluation of dental porcelain modified by bioactive glass

This study aimed at the chemical, microstructural and textural characterization of the sol–gel derived dental porcelain modified by bioactive glass and the evaluation of its bioactivity. Sol–gel derived specimens of the composite material were constructed and subjected to firing cycle. Specimens of bioactive glass and dental porcelain served as control. All the specimens were characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and N₂ porosimetry. The assessment of in vitro bioactivity was carried out by incubating the composite specimens in DMEM solution. Apatite formation was evaluated by SEM/EDS, FTIR and XRD analysis. Microstructural analysis by SEM revealed irregularly shaped particles with broad size distribution, while complex porei network with large pore volume and non-uniform pore size distribution was evident. N₂-adsorption isotherms were representative of non-nano-/meso-porous materials. A mixture of a- and b-wollastonite, apatite and leucite phases were detected by FTIR and Raman spectroscopy. The XRD analysis confirmed the previous results, though traces of cristobalite were identified too. The in vitro tests evidenced the bioactivity of the specimens in a 3-day-period. In conclusion, the physicochemical properties of the sol–gel derived composite result in a bioactive material, though further modifications need to be considered in order to fulfill the requirements of application in the clinical reality.     

Thermochemical Treatments for Protection of Steels in Chemically Aggressive Atmospheres at High Temperatures

Boronizing is a well-known thermochemical treatment process that has found applications in a variety of industries. Boride layers on Fe-alloys present high hardness values (∼ 1900 Hv), good wear properties and are resistant to various aggressive chemical environments. The mechanical behavior of boride layers on Fe-alloys has been well documented, but there seems to exist limited information on the chemical behavior of these coatings. We present in this paper the results of a systematic study of the chemical properties of boride layers, in aggressive environments that include dilute HCl, H₃PO₄, H₂SO₄ and HNO₃, acid solutions and vapors of molten Al alloy and Zn metals in various temperature ranges. Results indicated that with the exception of HNO₃ acid, the presence of boride layers on Fe-alloys, greatly improved their corrosion resistance. These results are discussed in terms of the potential applications they may have in various industrial sectors, including field tests carried out in fossil-fuel fired boilers.     

The Hafnium-Selective Extraction Fom a Zirconium(Hafnium) Heptafluoride Ammonium Solution Using Organophosphorus-Based Extractants

ABSTRACT

The suitability of the organophosphorus-based extractants, DiOPA, Ionquest 801 and D2EHPA was evaluated for the selective extraction of Zr and Hf from an (NH₄)₃Zr(Hf)F₇ acidic solution using both dispersive and pertraction solvent extraction (SX). A stock solution of (NH₄)₃Zr(Hf)F₇ was dissolved in either HCl or H₂SO₄ (0.1–8 M). The following extraction variables were investigated: type and concentration of the acidic solution, the contact time, and extractant to metal ratio. Subsequently, the stripping was investigated using (NH₄)₂CO₃, CaCl₂, H₂SO₄ and C₂H₂O₄ in the concentration ranges of 0–2 M. During extraction, scrubbing and stripping using D2EHPA, CaCl₂ and C₂H₂O₄, the Zr purity was increased from 97.2% to 99.0%. When extracting from 4 M H₂SO₄ with 9 wt% D2EHPA, a Hf selectivity of 32% was observed where after stripping with C₂H₂O₄ resulted in a 98.7% recovery of Zr. With 1.2 M CaCl₂ as stripping liquor, almost no Hf and 75% Zr stripping was obtained. During the pertraction 72% Hf and 44% Zr extraction was achieved after 180 min when extracting with 9 wt% D2EHPA from 4 M H₂SO₄. Pertraction based stripping with 1.2 M C₂H₂O₄ yielded 75% of both Zr and Hf, while stripping with 2 M CaCl₂ resulted in 58% Hf stripped with almost no Zr stripping.     

On the influence of grain shape on the cumulative deformations in sand under drained high-cyclic loading

The cumulative response of three granular materials with significantly different grain shape and surface characteristics (glass beads, natural sand with subrounded grains and crushed sand with very angular particles) but identical grain size distribution curve has been studied in drained cyclic triaxial tests. For each material, several tests with 100,000 cycles and different amplitudes, densities, average mean pressures and average stress ratios have been performed. In case of glass beads and natural sand, an approximately square relationship between the residual strain accumulation rates and stress or strain amplitude was found (${\stackrel{?}{\epsilon }}^{\mathrm{a}\mathrm{c}\mathrm{c}}$ ～ ${\left({\epsilon }^{\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}}\right)}^2$), while an almost proportional dependence was measured for the crushed sand (${\stackrel{?}{\epsilon }}^{\mathrm{a}\mathrm{c}\mathrm{c}}$ ～ ${\epsilon }^{\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}}$). The largest differences in the cumulative response of the three tested materials were observed regarding the pressure-dependence of ${\stackrel{?}{\epsilon }}^{\mathrm{a}\mathrm{c}\mathrm{c}}$. For glass beads and (less pronounced) for natural sand, the residual strain accumulation rates decreased with average mean pressure, while the opposite tendency was obtained for the crushed sand. At small pressures, the residual strains were much larger for the glass beads than for the natural sand and particularly the crushed sand, while these differences in the accumulated strains almost diminished at larger pressures. Independent of the shape and the surface characteristics of the particles, it was confirmed that the average stress ratio is the governing parameter of the cyclic flow rule. Finally, the parameters of the high-cycle accumulation (HCA) model proposed by Niemunis et al. (2005) were analyzed considering the grain shape parameters (aspect ratio, circularity) obtained from an automated grain shape analysis.     

Über die Abnahme der Tragfähigkeit von Verpreßankern unter Angriff von kalklösender Kohlensäure

Prediction of the reduction of the bearing capacity of cement grouted anchors under the attack of aggressive carbonic acid. The presence of lime attacking carbonic acid leads to a time dependent reduction of the bearing capacity of cement grouted anchors. This article deals with the experimental simulation of this solving attack and his influence on the bearing capacity of cement grouted anchors. At first simulation tests on cement bodies, placed in water and different soils subjected to CO₂‐attack, were carried out to determine the thickness of the developing corroded layer versus the application, concentration of carbonic acid and permeability of the surrounding soil. The experiments show, that the corroded layer grows mainly due to diffusion processes. Afterwards direct shear and pull out tests on corroded cement bodies were performed in order to determine the loss of bearing capacity of the anchoring force due to the corrosion depth. The angle of friction and the pull out force reduce only until a limiting value even by large corrosion depths is reached, which is higher than the applied residual value.