Finite Element Modelling of Creep Rupture on Grade 91 Steel using Monkman-Grant Ductility based Damage Model

Failure strain is a main parameter used in the ductility exhaustion based damage model in which the accuracy of the prediction is dependent on its input value. The experimental measured has indicated that the value of strain at fracture is extensively scattered, therefore may affect the prediction. This paper presents the result of creep rupture time using a modified creep damage model incorporating Monkman-Grant (MG) failure strain as an alternative to strain at fracture. Both strains at fracture and MG failure strain are separately employed in the damage model to predict the failure time of uniaxial smooth specimen and notched bar with different acuity ratios of 3.0 and 20. The FE model of the specimen is loaded under different stress values and the multiaxial failure strain at each stress level is estimated using Cock and Ashby void growth model. The predicted creep rupture time that is compared to the experimental data (in a range of 40-1000 hours) showing a good agreement within the scatter band of +/- factor of 2. Both approaches using strain at fracture and MG failure strain can be used in predicting the creep failure under uniaxial and multiaxial features. The advantage of using MG strain is that the laboratory creep testing can be interrupted prior to specimen fractured or once the secondary creep deformation occurs. Meanwhile, the determination of strain at fracture needs longer test duration where the test can be stopped only when the specimen broken

Kebolehbentukan-tikso aloi 2014 dengan penambahan Si dan pengurangan Cu

Dalam kajian ini, kebolehbentukan-tikso aloi aluminium (Al) 2014 dengan penambahan unsur silikon (Si) dan pengurangan unsur kuprum (Cu) dikaji. Kandungan Si dan Cu dalam aloi 2014 diubah suai supaya kriteria kebolehbentukan-tikso dapat dipenuhi. Kebolehbentukan-tikso aloi 2014 dan aloi Al-terubah suai diukur secara termodinamik dengan menggunakan pakej perisian JMatPro dan seterusnya dibuktikan secara uji kaji melalui analisis terma dan analisis fasa. Hasil kajian ini mendapati bahawa sifat kebolehbentukan-tikso aloi 2014 dapat dipenuhi dengan penambahan Si dan pengurangan Cu. Apabila kandungan Si dalam aloi 2014 bertambah, kandungan fasa eutektik pada titik ‘lutut’ tertinggi yang terbentuk di atas lengkung pecahan cecair meningkat dengan ketara, manakala julat suhu pemejalan pula semakin mengecil. Di samping itu, pengurangan Cu pula menyebabkan julat suhu pemprosesan untuk pembentukan-tikso menjadi semakin luas lalu mengakibatkan sensitiviti pecahan cecair pada titik ‘lutut’ tertinggi menurun. Selain pembentukan fasa Al2Cu dan fasa θ-Al5Cu2Mg8Si6, kemunculan fasa π-Al8FeMg3Si6 dengan struktur yang padat hasil daripada pengurangan Cu juga dijangka menyumbang kepada peningkatan sifat mekanik aloi Al-terubah suai. Akhir sekali, aloi Al-terubah suai tersebut dijangka mampu digunakan untuk menghasilkan komponen otomotif seperti rod penyambung, aci sesondol dan aci engkol melalui proses pembentukan-tikso

Observing the behaviour of reinforced magnesium alloy with carbon-nanotube and lead under 976 m/s projectile impact / M.F. Abdullah ...[et al.]

This paper presents the effects of reinforced magnesium alloy, AZ31B with carbon-nanotube (CNT) and lead (Pb), in terms of ballistic resistance. Magnesium alloys possess high energy absorption capability for impact resistance. However, its capability is limited and needs to be enhanced to resist ballistic impacts. The addition of a reinforcement material within the magnesium alloy, such as CNT or Pb, can improve impact resistance. This study is divided into two ballistic test methods, namely experiment and simulation. The samples involved are the original AZ31B and reinforced AZ31B with CNT and Pb. The projectile type used for ballistic testing was a 5.56 mm FMJ NATO at a velocity of 976 m/s and the thickness of the plate was 25 mm. The aim is to study the ability of the plate against the ballistic resistance. The ballistic experiment utilises a high speed camera, at 100,000 fps, to capture the impact occurring on the plate’s surface. A Cowper-Symonds model is used for the ballistic simulation and indicates the ballistic resistance of the reinforced AZ31B with increments of CNT and Pb. The velocity of the projectile penetrating through the plate was reduced by over 45% compared to the original AZ31B alloy. Reinforcement using CNT and Pb on AZ31B improved the ballistic resistance behaviour and therefore, this material is suitable for use on ballistic panel

Finite Element Modelling of Creep Rupture on Grade 91 Steel using Monkman-Grant Ductility based Damage Model

Failure strain is a main parameter used in the ductility exhaustion based damage model in which the accuracy of the prediction is dependent on its input value. The experimental measured has indicated that the value of strain at fracture is extensively scattered, therefore may affect the prediction. This paper presents the result of creep rupture time using a modified creep damage model incorporating Monkman-Grant (MG) failure strain as an alternative to strain at fracture. Both strains at fracture and MG failure strain are separately employed in the damage model to predict the failure time of uniaxial smooth specimen and notched bar with different acuity ratios of 3.0 and 20. The FE model of the specimen is loaded under different stress values and the multiaxial failure strain at each stress level is estimated using Cock and Ashby void growth model. The predicted creep rupture time that is compared to the experimental data (in a range of 40-1000 hours) showing a good agreement within the scatter band of +/- factor of 2. Both approaches using strain at fracture and MG failure strain can be used in predicting the creep failure under uniaxial and multiaxial features. The advantage of using MG strain is that the laboratory creep testing can be interrupted prior to specimen fractured or once the secondary creep deformation occurs. Meanwhile, the determination of strain at fracture needs longer test duration where the test can be stopped only when the specimen broken

Characterising Ballistic Limits of Lightweight Laminated-Structure as a Protective Panel for Armoured Vehicle / N.A. Rahman...[et al.]

This study investigates the ballistic performance of aluminium alloy Al7075-T6 and magnesium alloy AZ31B served as the intermediate layer in triple-layered laminated panel using computational analysis. Aluminium and magnesium alloys offer a considerably potential for reducing the weight of an armoured vehicle body due to low densities and high energy absorption capabilities. The poor ballistic performance of these materials can be improved by layering with the high strength steel, Ar500. A commercial explicit finite element code was implemented to develop triple-layered panels impacted by a 7.62 mm armour piercing projectile at velocity range of 900 to 950 m/s. Two models were constructed where aluminium alloy and magnesium alloy served as intermediate layer in the first model and the second model respectively. The ballistic performance of each model in terms of ballistic limit velocity and depth of penetration was evaluated. Considering the 25% existing armour vehicle weight reduction, it was found that magnesium alloy has equivalent ballistic limit to that of aluminium alloy which is at 1020 m/s. At the standard projectile velocity, aluminium stopped the projectile at 24 mm depth and magnesium stopped at 25 mm. Thus, lightweight materials can be suitable combinations for designing lighter armoured vehicle panel without neglecting its ballistic performance

INVESTIGATIONS ON THIXOJOINING PROCESS OF STEEL COMPONENTS

This research is to develop a carbon composite prepared from carbon coir fibers that is reinforced with epoxy resin. Carbon coir fibers were taken from three types of coir fiber specifically designated as CKCF, CYCF and CRCF. The samples were prepared using epoxy resin reinforced with carbon at different weight percentages for three types of coir fiber starting with 0wt.%, 2wt.%, 4wt.%, 6wt.%, 8wt.% and 10wt.%. The mechanical properties such as tensile stress and impact strength were used to characterize all the samples. The morphological study of reinforced samples was also conducted in this research using a SEM machine. The characteristics of all the composite materials were also investigated and discussed. It was determined that the CKCF sample exhibited better mechanical properties than the other coir fiber composites, having a higher average tensile stress value at 11.80MPa and higher impact strength values ranging from 268J to 276J at different carbon content. CKCF with 10wt% AC content had a tremendous impact strength compared with CYCF and CRCF

The Effect of Surface Texture on the Joint Shear Strength of AR500 Steel and AA7075 / M. N. Muhamed...[et al.]

AA7075 aluminium alloy brazing joint panels caused by shear loading. The use of steel and aluminium laminated metal composite is increasingly popular since they are well known for lightweight application and stiffness properties and this makes them the material of choice in automotive industry. However, the formation of reaction layer phases has limited the application of this method of joining due to the adverse effect of these phases on the strength of the joint. In this work, AR500 steel and AA7075 aluminium alloy interface joint were fabricated by torch brazing method using Al-Si-Zn base material as its filler metal for different types of surface conditions. The joining was evaluated for shear strength performance. The experimental results showed that the highest shear strength for the panel was recorded at 8010 N. Fractures were mostly seen at the joint interface area. In general, the torch brazing process with different surface joining conditions, had facilitated the joining of these dissimilar metals while improving the mechanical properties of the joint

Effect of Steel Fibres And Wire Mesh Reinforcement on Flexural Strength and Strain Energy Steel-Epoxy-Aluminium Composite Laminates / W. N. M. Jamil ...[et al.]

This paper evaluates the effect of reinforcement materials on the flexural strength and strain energy in metal laminates under bending tests. Traditionally, high hardness monolithic steel has been utilised in lightweight armoured vehicles. In order to increase the performance of the armoured plates, their weight is reduced by incorporating adhesive bonding metal laminates technology. Simultaneously, the application of metallic fibres in construction is also being developed for the same purpose. Therefore the incorporation of metallic fibres in adhesive layer can reduce the weight and increase the strength of armoured panels. It is important to assess and predict the flexural strength and strain energy in the metal laminated armour. The effects of steel fibres and stainless steel mesh were investigated through flexural tests. The flexural strength was assessed by a three-point bending test using a universal testing machine. The strain energy was measured from the stress-strain curve using the data from the bending test. From the results, the steel fibre-reinforced and wire mesh-reinforced composite laminates exhibited higher flexural strength compared to non-reinforced composite laminate by 10% and 9%, respectively. Further, steel fibre-reinforced and wire mesh-reinforced composite laminates had higher strain energy at 23% and 31% compared to non-reinforced composite laminate, respectively. Cracks occurred at the back layer of the aluminium alloy and propagated vertically through the aluminium and adhesive layer and stopped at the steel layer. This is due to the higher strength and ductility of the steel in withstanding the load. Reinforcement with steel fibres and wire mesh enabled the metal laminate to bear higher load, while decreasing the damage and delamination due to its higher strength, strain energy and ductility compared to the non-reinforced composite laminate. The reinforcement materials have the potential to produce tough adhesive-bonded metal laminates for ballistic impact applications

Effect of Aluminium Content on the Tensile Properties of Mg-Al-Zn Alloys

ABSTRAC

Effect of aluminium content on the tensile properties of Mg-Al-Zn Alloys

The aim of this study is to investigate the effect of aluminium content on microstructure, tensile properties and work hardenability of Mg-Al-Zn alloys. Two types of magnesium alloys were investigated i.e. AZ31 and AZ61, where the aluminium contents were 3% and 6%, respectively. Microstructure observation revealed that higher aluminium content decreases the grain size and increases the volume of Mg17Al12 precipitations. From the tensile test, AZ61 demonstrated higher yield stress and tensile strength while maintaining the elongation as compared to AZ31. The work hardening rate for AZ61 was also greater as compared to that of AZ31