Bolt Load Retention Research Articles

Effect of Sn Content on Heat Resistance of Mg-3%Al-1%Si Alloy for Casting

Magnesium alloys have the characteristic with high specific strength and lightweight property, it is widely used for auto mobile industry. Heat-resistant magnesium alloy is focused as a suitable material for weight reduction of the engine and power train parts in automotive field. In this study, microstructure and heat-resistant property in Mg-3mass%Al-1mass%Si (Mg-3%Al-1%Si) alloy with containing large amount of Sn (tin) were investigated. The alloys produced by permanent mold casting were investigated by optical microscope (OM), scanning electron microscopy (SEM) and measuring of bolt load retention at 423K. The heat-resistant property of Mg-3mass % Al-1mass % Si alloy with containing 6-13masss%Sn was higher compared with Sn free alloy and conventional Magnesium alloys (e.g. AZ91 and AM60 alloys).

Modeling Bolt Load Retention of Ca Modified AS41 Using Compliance-Creep Method

Adequate quantification of the degree of fastener clamp load retained at bolted joint of Mg-Al alloys is crucial to develop new elevated temperature resistant Mg-alloys. Several attempts have been made in the past to model Bolt Load Retention (BLR) behaviour of Mg-alloys using different approaches. It must be mentioned that whereas these models attempt to predict BLR of the alloys investigated, the results of the models differ in most cases with the experiments by great margin. The BLR behaviour of Mg-alloy is geometry and material dependent. This means that, the configuration of the test sample, the compliance of the bolt/joint and creep response of the material under investigation play important role in determining the joint response under load and temperature. In this work, BLR and creep behaviour of Ca modified AS41 is investigated and compared to that of Mg4Al and AS41. A compliance-creep approach is used to model the response of these Mg-Al alloys at bolted joints. The model prediction of the BLR response and experimental results as obtained in this work are in good agreement. AS41+0.15 % Ca shows improved creep and BLR properties up to 175 °C. A correlation between the microstructures, creep and BLR results reveal that the formation of a ternary CaMgSi phase is responsible for the improved elevated temperature behaviour.

Bolt Load Retention and Creep Response of AS41 Alloyed with 0.15 % Ca

Bolt Load Retention and Creep Response of AS41 Alloyed with 0.15 % Ca

Effect of Prior Deformation on Creep Behavior of a Die-Cast Mg-Al-Ca Alloy

The creep of die-cast Mg-Al-Ca alloys is characterized by the pronounced decrease in creep rate during the transient region. Higher creep rates immediately after the stress application for the alloys can result in the degradation of bolt-load retention in the automotive powertrain applications. In this study, the effect of prior deformation on creep behavior was investigated for the Mg-Al-Ca AX51 (X representing calcium) die-cast alloy, where the prior deformation was introduced by using the creep machine at temperatures of 423 and 473 K. The creep curves of the specimens with the prior deformation were compared with that of the as die-cast specimen at the creep testing condition of 423 K and 80 MPa. It was found that the prior deformation introduced by the creep machine is not effective to decrease the creep rates for the alloy. The obtained results of creep behavior are discussed on the basis of dislocation movements during creep.

A Review on Bolt Load Retention Test of Magnesium Alloys

The bolt load retention (BLR) test fixtures and behaviors of Mg alloys by main research teams are reviewed. Parts of BLR test results are also presented. Since creep properties are relevant to BLR, an approach to predicting BLR behaviors from creep curves is briefly introduced. The BLR test fixtures and procedures in our study are also shown.

Modeling of Bolt Joint Behavior of Cast Aluminum Alloy (A380-T5) by Coupling Creep and Plasticity in Finite Element Analysis

Aluminum casting alloys exhibit creep behavior when the materials are exposed to high temperature and load. In this article, the stress- and temperature-dependent creep behavior of a die casting A380-T5 aluminum alloy was simulated using a classical constitutive model. The bolt-load retention behavior of the material was analyzed in a head bolt joint in an aluminum engine under thermal cycle condition using the finite element method. In this simulation, transient thermal analysis was performed first to calculate the metal temperature at the head bolt joint as a function of time during engine thermal cycling. This temperature was then input as the thermal loading in the subsequent structural analysis to calculate its effect on the bolt-load retention. The finite element analysis (FEA) model for the bolt-load retention simulation includes not only the plasticity in all metal components but also the creep properties of head bolt threads in the cast aluminum engine block. The FEA model was validated by good correlation between the predicted head bolt-load loss and the experimental measurement during engine thermal cycling. The simulation results also indicated that creep in the head bolt threads of cast aluminum engine block was mainly responsible for the load loss in the head bolt joint.

A REVIEW ON STRESS RELAXATION AND BOLT LOAD RETENTION OF MAGNESIUM ALLOYS FOR AUTOMOTIVE APPLICATIONS

An attempt has been made to comprehensively review the stress relaxation and bolt load retention (BLR) test procedures and behaviour of Mg alloys. The aim is to provide a basis for a common test procedure for BLR testing of Mg alloys for automotive applications. The review indicates that bolt load retention behaviour of Mg alloys, an important engineering design property, depends on both compressive creep property and the compliance of the bolt joints. The stress in Mg components in bolt joints is usually highly non-uniform and the magnitude of the stress is sometimes high, up to yield or even above yield strength. BLR behaviour can be understood qualitatively from these characteristics, but currently, BLR cannot be quantitatively predicted from stress relaxation or creep test results. The literature review shows that there is a need for a common BLR fixture and BLR specimen (shape and dimensions) representative of the joined components in automotive applications. Needs for future research on the effects of sample geometry and initial load on BLR behaviour and on modelling BLR are discussed. Recommendations are made for a cylindrical common BLR test specimen based on the results from the literature review and from a survey of typical bolt joints.On a essayé de revoir d’une manière compréhensible les procédures d’essai de relaxation de contrainte et de rétention de la charge du boulon (BLR) et le comportement d’alliages de Mg. Le but est de fournir une base pour une procédure commune d’essai pour l’évaluation de la BLR d’alliages de Mg pour applications dans l’industrie automobile. La revue indique que le comportement de rétention de la charge du boulon des alliages de Mg, une propriété importante de la conception technique, dépend à la fois de la propriété de fluage en compression et de l’élasticité des joints de boulon. La contrainte des composantes en Mg des joints de boulon est habituellement très variée et la grandeur de la contrainte est quelquefois élevée, jusqu’à la limite élastique ou même au-delà. On peut comprendre qualitativement le comportement de BLR à partir de ces caractéristiques mais actuellement, on ne peut pas prédire quantitativement la BLR à partir des résultats d’essai de relaxation de la contrainte ou de fluage. La revue de littérature montre qu’on a besoin d’un dispositif d’évaluation commun et d’un échantillon de BLR (forme et dimensions) représentatif des composantes jointes pour applications dans l’industrie automobile. On discute du besoin de recherches futures sur l’effet de la géométrie de l’échantillon et de la charge initiale sur le comportement et la modélisation de BLR. On recommande un échantillon d’essai commun cylindrique de BLR basé sur les résultats de la revue de la littérature et d’un relevé de joints de boulon typiques.

Mathematical Model for Relaxation in High-Strength Bolted Connections

High-strength bolted connections with protective coatings are used extensively in bridges. The relaxation in high-strength bolts due to creep in the coating can reduce the shear capacity of the connection. In a recent bridge application using high-strength bolted connections with hot-dip galvanized coating, a loss in the bolt clamping force was observed. Tests have been conducted to evaluate the effect of coating thickness on the bolt clamping force. The reduction in the bolt force for coatings up to 0.508 mm (20 mils) has been shown to be as large as four times that for bare steel. A mathematical model is developed to evaluate the relaxation effect in the high-strength bolted connections. The analytical predictions are compared with experimental data, which shows a very good agreement. An approach is presented to predict the bolt-load retention based on the relevant creep data. The model developed in this paper can also be used for other coating systems to predict the loss of the bolt force due to the creep occurring in the bolted connections.