Kamel Chaoui

Mathematical modeling for turning on AISI 420 stainless steel using surface response methodology

In this study, an attempt has been made to statistically model the relationship between cutting parameters (speed, feed rate and depth of cut), cutting force components (Fx, Fy and Fz) and workpiece absolute surface roughness (Ra). The machining case of a martensitic stainless steel (AISI 420) is considered in a common turning process by means of a chemical vapor deposition–coated carbide tool. A full-factorial design (43) is adopted in order to analyze obtained experimental results via both analysis of variance and response surface methodology techniques. The optimum cutting conditions are achieved using mutually response surface methodology and desirability function approaches while the model adequacy is checked from residual values. The results indicated that the depth of cut is the dominant factor affecting (Fx: 86%, Fy: 58% and Fz: 81%), whereas feed rate is found to be the utmost factor influencing surface roughness behavior (Ra: 81%). In addition, a good agreement between the predicted and measured cutting force components and surface roughness was observed. The results are also validated experimentally by determining errors (Fx: 6.51%, Fy: 4.36%, Fz: 3.59% and Ra: 5.12%). Finally, the ranges for optimal cutting conditions are projected for serial industrial production.

Failure Analysis of Polyethylene Gas Pipes

Natural gas transmission and distribution industry is using pipes of different origins to transport hydrocarbons under pressure. The use of poly- meric material such as polyethylene (PE) made it possible to achieve significant profits in construction times and installation costs. However, some catastrophic failures took place for various reasons. The objective of this study is to highlight the various mechanisms of rupture of PE pipes in service and in laboratory con- ditions. It is clear that at least two mechanisms control PE pipe failures based on results cumulated in operating conditions. They are nominally ductile and brittle mechanisms respectively characterizing short and long-term failures. Several laboratory tests are used to extract design data for long-term failure-type predi- ction based on stress and time to failure relationship. It remains difficult to assess the relation between creep and fatigue loadings on the one side. On the other side, the manufacturing process of the test specimens (extruded pipes and compression molded sheets) influences considerably the obtained performance for viscoelastic materials subjected to working conditions. When analyzing different results, it is found that there is a certain correlation between failure times under both constant and fluctuating loading patterns and moreover, fatigue can be used as an accelerating agent of brittle fracture which normally occurs in the long-term span and under low load levels. Brittle-to-ductile transition is studied under fatigue crack propagation mode using an energy criterion. It is found that the approach leads to critical energy rates of 211 and 695 J/m² for brittle and ductile regimes respectively. The brittle fracture damage zone is characterized by a single craze made up by locally drawn fibers and dispersed

Reliability Assessment of Pipelines using Phimeca Software

The present work deals with lifetime management of underground pipeline for safe hydrocarbon transport. Reliability PHIMECA soft tool is used for assessing the tubular structure under active corrosion. Basically, three parts are presented. First, a theory of reliability methods is developed to make in evidence the design philosophy. Second, the concept of reliability analysis under PHIMECA soft is given to sort out the mechanical and probability models for a determined limit state function. Finally, a case study applied to an underground pipeline under severe loading and active corrosion is investigated in order to analyze the reliability. A PHIMECA report on the obtained result is given. The former approach concerns the experimental characterization of residual stress distribution in large diameter pipes to be coupled with a corrosion model. Along the pipe lifetime, the residual stress relaxation is involved due to the loss of pipe thickness as material layers are consumed out by corrosion.

Investigation of microstructure and mechanical properties of phosphocalcic bone substitute using the chemical wet method

Selection of calcium phosphate base materials in reconstructive bone surgery is justified by the surprising similarities in chemical compositions with human bones. The closest to natural apatite material is the hydroxyapatite (HAp) which has a chemical composition based on calcium and phosphate (Ca10(PO4)6(OH)2). In this study, HAp is synthesized using the wet precipitation method from hydrated calcium chloride (CaCl2,12H2O) and di-sodium hydrogen phosphate di-hydrate (HNa2PO4,2H2O). The powder is calcinated at 900°C and 1200°C in order to compare with sintered condition at 1150°C. Vickers microhardness tests and X-ray diffraction analyzes are used for the characterization of the crystalline material. Mechanical properties (Hv, σe, σr, and KC) and the degree of crystallinity (Xc) are discussed according to heat treatment temperatures. Results indicate that heat treating the powder at 1200°C increased crystallinity up to 72%. At the same time, microhardness increased with temperature and even outmatched the sintered case at 1150°C. Fracture toughness is ameliorated with increasing heat treatment temperature by more than two folds.Selection of calcium phosphate base materials in reconstructive bone surgery is justified by the surprising similarities in chemical compositions with human bones. The closest to natural apatite material is the hydroxyapatite (HAp) which has a chemical composition based on calcium and phosphate (Ca10(PO4)6(OH)2). In this study, HAp is synthesized using the wet precipitation method from hydrated calcium chloride (CaCl2,12H2O) and di-sodium hydrogen phosphate di-hydrate (HNa2PO4,2H2O). The powder is calcinated at 900°C and 1200°C in order to compare with sintered condition at 1150°C. Vickers microhardness tests and X-ray diffraction analyzes are used for the characterization of the crystalline material. Mechanical properties (Hv, σe, σr, and KC) and the degree of crystallinity (Xc) are discussed according to heat treatment temperatures. Results indicate that heat treating the powder at 1200°C increased crystallinity up to 72%. At the same time, microhardness increased with temperature and even outmatched th...

Identification of Bi-Materials Mechanical Characteristics Using the Virtual Fields Method

One method of identifying parameters governing the behaviour of an elastic material covers the Virtual Fields Method (VFM). However, this method has been validated for only homogeneous materials. In the case of compound materials, the presence of strong gradients strains near the interface limits the potential of this method, which requires some adjustments. This work focuses on the validation of the VFM applied to a Bi-Material composed of Polymer and Epoxy. The results obtained are in correlation with the characteristics of components used

Degradation and Failure of Some Polymers (Polyethylene and Polyamide) for Industrial Applications

The use of polymeric material such as polyethylene (PE) and polyamides (PA) made it possible to achieve significant profits in design construction times and installation costs. The objective of this study is to highlight the various mechanisms of rupture of polyethylene pipes in service and in laboratory conditions under fatigue and creep loadings. It is known is some cases that at least two mechanisms control PE pipe failures based on results cumulated in operating conditions. They are nominally ductile and brittle mechanisms respectively characterizing short and long-term failures. Several laboratory tests are used to extract design data for long-term failure-type prediction based on stress and time-to-failure relationship. It remains difficult to assess the relation between creep and fatigue loadings on one side. On the other side, the manufacturing process of the test specimens influences considerably the obtained performance for viscoelastic materials subjected to working conditions and environmental effects. Brittle-to-ductile transition is studied under fatigue crack propagation mode using an energy criterion. The brittle fracture damage zone is characterized by a single craze made up by locally drawn fibers and dispersed voids whereas ductile rupture is rather dominated by highly yielded material and significantly transformed matter as observed under polarized-light microscopy. The assessment of polyethylene pipe and polyamide parts failure mechanisms is to contribute to a better understanding of effects of other external chemical agents such as solvents in degrading the pipe overall resistance. Recent results from environmental stress cracking of PE pipe and exposed polyamide PA66 to detergent will be presented and correlated to mechanical properties degradation.

Effects of Aggressive Chemical Environments on Mechanical Behavior of Polyethylene Piping Material

During the construction process of fluid handling structures, material selection for pipe applications is an important step. Both natural gas and drinkable water are mainly transported in underground polyethylene (PE) pipe networks. It is known that the interaction between materials like HDPE (high density PE) and its service environment represents critical factors of influence on the structure behaviour for short and long terms. The goal of this study is to establish the effect of some chemical agents on the mechanical properties of PE tubes for underground use. The results are discussed basing on the stress—strain curves and according to the mechanical resistance to aggressive environments. It was found that the environments consisting of solvents show degradation of the mechanical properties of tubes and a structural weakening of the rigidity of the system is observed. Organic solvents have significant oxidizing capacity which weakens polyethylene chains, whereas acids such as H2SO4 have less influences on the mechanical properties compared to organic solvents. In the case of crude oil, results show moderate effect although it is known to attack many polymers. In the case of solvents, the elasticity modulus is reduced up to 64% for crude oil which represents a serious problem for the underground polyethylene networks. Design equations of such structure should take into account serious adjustments of long term loads when polyethylene is exposed to aggressive environment.