Heraldo S. da Costa Mattos

Failure Pressure Estimations for Corroded Pipelines

The goal of the present paper is to propose a simple methodology to estimate the failure pressure of thin-walled metallic pipelines with arbitrary localized corrosion damage. This methodology is conceived as a preliminary tool for a quick analysis of the structural integrity of real corroded pipelines. Due to the different possible geometries of the corroded region, the exact analysis of this kind of problem can be very complex (in general using an elasto-plastic finite element simulation). The idea is to obtain an approximate exact analytical solution of the problem for any arbitrary geometry of the corroded region considering elasto-plastic constitutive equations and a factor that accounts for the stress concentration due to the metal loss caused by corrosion. With a simple expression, a reasonable lower limit for the failure pressure can be obtained.

Modelling low-cycle fatigue tests using a gradient-enhanced continuum damage model

This study is concerned with the modelling of uniaxial low-cycle fatigue tests using a gradient-enhanced continuum damage model. The aim of the paper is to show that a simple but adequate descripti...This study is concerned with the modelling of uniaxial low-cycle fatigue tests using a gradient-enhanced continuum damage model. The aim of the paper is to show that a simple but adequate description can be performed using such kind of phenomenological approach. The model accounts for the coupling between plasticity and damage, including a mathematically consistent description of the softening behaviour and size dependency. It successfully predicts low-cycle fatigue and can deal with regular cycles. A consistent procedure to identify experimentally the constitutive parameters that appear in the theory is proposed. Lifetime predictions for different loading amplitudes are compared with experimental data for two aluminium alloys showing a good agreement. The one-dimensional model can be interpreted as a particular version of a more general gradient-enhanced damage model, which is summarized at the end of the paper.

LOAD RATE EFFECTS IN ADHESIVE SINGLE LAP JOINTS BONDED WITH EPOXY/CERAMIC COMPOSITES

THE PRESENT PAPER IS CONCERNED WITH THE ANALYSIS OF THE EFFECT OF THE LOADING RATE IN A PARTICULAR CLASS OF SINGLE LAP JOINTS USED IN THE OIL INDUSTRY. THE ADHESIVE/ADHEREND SYSTEM CONSISTS OF ASTM A36 STEEL PLATES BONDED WITH AN EPOXY/CERAMIC COMPOSITE. THE LOADING RATE SENSITIVITY IS ANALYSED CONSIDERING TWO DIFFERENT SITUATIONS: (I) STRAIN CONTROLLED QUASI-STATIC RUPTURE TESTS AND (II) APPLICATIONS IN WHICH THE JOINT MAY OSCILLATE LIKE A SPRING. THIS SECOND SITUATION IS MOTIVATED BY A SPECIFIC APPLICATION: THE TRANSPORT OF AN ETHANOL RESERVOIR BY A CRANE USING A SPECIAL TRUSS LIFTING SYSTEM ATTACHED TO THE TANK THROUGH BONDED JOINTS. QUASI-STATIC TENSILE TESTS ALLOW OBSERVING A RATE-DEPENDENT BEHAVIOUR OF THE JOINT WITH HIGHER STRENGTHS FOR HIGHER CROSS-HEAD VELOCITIES. AN ALGEBRAIC EQUATION IS PROPOSED TO PREDICT THE DEPENDENCE OF THE RUPTURE FORCE ON THE ELONGATION RATE IN TENSILE TESTS AND THE MODEL PREDICTIONS ARE IN GOOD AGREEMENT WITH EXPERIMENTAL RESULTS. HOWEVER, IN THE CASE OF THE TRANSPORT OF A TANK WITH MASS M (SITUATION (II)), THE LIFTING SYSTEM CANNOT BE ONLY DESIGNED TO RESIST THE STATIC LOAD (THE WEIGHT). FAST LOADING MAY INDUCE VIBRATION. LIKE IN A SPRING-MASS SYSTEM, EVEN A VERY SMALL OSCILLATION OF THE JOINT INDUCES A DYNAMIC LOAD THAT IS HIGHER THAN THE STATIC LOAD. A SIMPLE ANALYSIS ALLOWS PROPOSING CONDITIONS FOR A SAFE OPERATION IN THIS CASE.

Influence of Graphite Powder and Carbon Black Weight Percentages on the Electrical Properties of Epoxy Composite Plates

There is a growing demand for polymeric composite materials, mainly, in industrial applications. For instance, bipolar plates for polymer electrolyte fuel cell in automobile applications. This kind of composite can replace with lower cost and greater efficiency metallic components. The basic requirement is that the composite must possess adequate electrical and mechanical properties for the particular application. The goal of the present paper is to analyze the effect of graphite powder and carbon Black weight percentages on the electrical properties of epoxy composite plates. Electrical conductivity tests were performed in different composites. This study shows that is possible to obtain a semiconductor behavior with both epoxy/graphite and epoxy/Carbon Black composites.