Lifetime Estimation Method of Polyethylene Pipe Based on the Full Notch Creep Test

The Creep Crack Growth (CCG) of polyethylene pipe directly limits its long-term lifetime. The long-term lifetime estimation of polyethylene pipe was proposed by combining the crack kinetics and Paris-Erdogan crack growth model. According the Full Notch Creep Test (FNCT) to measure the relationship between the crack opening displacement COD and the test time ti of the preformed PE ring notch specimens during creep tension, and the crack growth rate da/dt, stress intensity factor KI can be calculated, then the inherent parameters A, m of PE materials can be obtained through the Paris-Erdogan crack growth model. Finally, the relationship between the crack depth af and the crack growth time tCCG of polyethylene pipes in the long-term use process can be extrapolated. The test result shown that, when the specification of PE pipes were dn110-sdr11, if there was an initial crack with a depth of aini = 0.4mm on the outer wall of the pipe, and under the continuous action of pipe pressure with p = 0.4 MPa, when the depth crack of PE1 and PE2 pipes expanded to 0.8mm, it needed to maintain or replace the defective pipe section, and the lifetime of the pipes were 22.89 and 20.03 years. Respectively, if the pipes were not maintained and replaced in time, and it will exist medium leakage only takes 14.13 and 12.44 years.

Additive Manufacturing of 316L Stainless Steel by a Printing-Debinding-Sintering Method: Effects of Microstructure on Fatigue Property

Additive manufacturing (AM) technology has been broadly applied to the fabrication of metallic materials. However, current approaches consume either high energy or large investment that considerably elevates their entry threshold. An economic extrusion-based AM method followed by debinding and sintering could efficiently produce the metal parts with relatively low cost and high material utilization. However, an in-depth analysis of the fatigue performance of the component built by such a technology has been little documented so far. Herein, the 316L stainless steel was fabricated throughout the printing-debinding-sintering (PDS) pathway and its fatigue properties were comprehensively assessed. Tensile and flexural fatigue tests were conducted to reveal the fatigue strength and fractural behaviors under different loading conditions, while the fatigue crack growth (FCG) test was performed to quantify the crack propagation. The results indicated the number of 105 cycles can be reached for the tensile specimens under the fatigue loading of 120 MPa, whereas 1.37 × 105 cycles were endured by the flexural specimens under 150 MPa. The fractural morphology indicated an adverse impact of the pore-induced voids on the tensile fatigue crack propagation, but such a drawback could be alleviated in the flexural loading condition. The FCG test unveiled the crack growth rate with the number of cycles and determined the material-related coefficients in the fatigue crack growth model. The research findings provided valuable insights into the effects of the PDS process and microstructures on the resultant fatigue properties of the metal component.

Fatigue crack growth prediction model under variable amplitude loading conditions

Crack size prediction under variable amplitude loading is a very complex process, which is also important for life prediction in engineering. A crack growth model considering different stress ratio for fatigue remaining life prediction is proposed in this paper. The model utilizes stress ratio to describe the variable loading sequences, which makes the calculation greatly simplified. The rain-flow method is utilized to characterize the load sequence effects under variable amplitude loading. In addition, particle filter is utilized to estimate the model parameters describing the crack growth. Finally, case study indicates that the proposed approach is efficient in predicting crack growth and fatigue remaining life.

Influence of Microscopic Effects on the Static Tensile Strength of Gray Cast Iron HT200 Specimens

Gray cast iron HT200 material is a kind of pearlitic gray cast iron. Flake graphite in the gray cast iron greatly destroys the integrity of the matrix and affect the static strength. The influence of microscopic effects on the tensile static strength of gray cast iron HT200 specimens is investigated. The microstructures are observed by the scanning electron microscope. The failure tests are done under the static loads for the cylinder specimens of gray cast iron HT200. Then, an energy density zone (EDZ) model is applied to the simulation of the fracture process of the specimens. The energy density zone model is a macro/micro-trans-scale crack growth model that can depict a fracture process from an initial microdefect at the microscale to the final break at the macroscale. Three scale transitional functions as well as the size of the initial microdefect in the model represent the microscopic effects in a fracture process. Three scale transitional functions are speculated in view of the physical failure mechanisms. Two other material parameters in the model are determined from the test data. Thereby, the fracture process of gray cast iron specimens is numerically simulated, and the static strength values are calculated. The calculated values of static strength of gray cast iron specimens are identical to the test values. It is seen that the energy density zone model can accurately describe a fracture process of brittle materials like gray cast iron. In addition, the calculated results show that the microscopic effects did affect the static strength of gray cast material.

Prediction of Rolling Contact Fatigue Behavior in Rails Using Crack Initiation and Growth Models along with Multibody Simulations

Rolling contact fatigue (RCF) is a common cause of rail failure due to repeated stresses at the wheel-rail contact. This phenomenon is a real problem that greatly affects the safety of train operation. Preventive and corrective maintenance tasks have a big impact on the Life Cycle Cost (LCC) of railway assets, and therefore cutting-edge strategies based on predictive functionalities are needed to reduce it. A methodology based on physical models is proposed to predict the degradation of railway tracks due to RCF. This work merges a crack initiation and a crack growth model along with a fully nonlinear multibody model. From a multibody assessment of the vehicle-track interaction, an energy dissipation method is used to identify points where cracks are expected to appear. At these points, crack propagation is calculated considering the contact conditions as a function of crack depth. The proposed methodology has been validated with field measurements, conducted using Eddy Currents provided by the infrastructure manager Network Rail. Validation results show that RCF behavior can be predicted for track sections with different characteristics without the necessity of previous on-track measurements.