Walid
@ju.edu.jo
Associate professor at the department of Industrial Engineering/ Engineering
The University of Jordan
EDUCATION
PhD, Chalmers University of Technology, Gothenburg, Sweden 1999 - 2004
PhD degree in materials science and engineering
I did my PhD studies in the field of powder metallurgy (liquid phase sintering)
Thesis: Tailoring of liquid phase sintering and microstructure of sintered steel
Chalmers University of Technology, Gothenburg, Sweden 1997-1999
Master of Science in materials science and engineering
Thesis: Metalized Plastics for Space Applications
Jordan University of Science and Technology, Irbid, Jordan 1991 - 1996
Bachelor’s degree in mechanical engineering (162 credit hours)
RESEARCH, TEACHING, or OTHER INTERESTS
Materials Science, Metals and Alloys
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Walid Khraisat and Wisam Abu Jadayil
Elsevier BV
W. Khraisat and H. Borgström
Springer Science and Business Media LLC
W. Khraisat
Informa UK Limited
Abstract The effects of quasi-static strain rates on the tensile properties of two commercial ferrite-martensite dual-phase DP 600 and DP 800 steels were investigated using strip-shaped samples. The investigation was done by uniaxial tensile tests, covering applicable quasi-static strain rates. The two dual-phase steels show positive strain rate sensitivity. It is found that, as the flow stress increases, the strain-rate sensitivity exponent m decreases. The drop in the strain-rate sensitivity exponent m with strain is largely attributed to the decreased true strain rate caused by the increased instantaneous length of the specimen as the deformation progresses. To better describe the flow behavior of DP steels, a relationship combining the effect of both strain hardening exponent n and strain-rate sensitivity exponent m on the slope of the stress-strain is correlated. A good agreement between the extended Hollomon model and experimental tensile test data from stress-strain measurements is found.
Walid Khraisat, Wisam Abu Jadayil, and Nathir Rawashdeh
Springer Science and Business Media LLC
Nathir A. Rawashdeh, Jumana M. Abu-Khalaf, Walid Khraisat, and Shireen S. Al-Hourani
Informa UK Limited
ABSTRACT In any pharmaceutical packaging process, error rates must be kept very low to prevent defective or incorrect medicine from reaching the consumer. Published articles include a focus on the inspection of ampoule content for the presence of contaminants. Methods of inspection include optical cameras that record sequential images to detect the movement of floating objects via feature extraction and classification. Other methods employ spectral imaging and dying of ampoules to detect cracks. Thermal imaging is also used to inspect structural integrity and mechanical stress; however, this approach is marked by relatively high cost. This paper describes the enhancement of an optical vision-based inspection system for a glass ampoule packaging process. The developed solution involves a reconfiguration of the illumination system of the ampoule trays as well as reprogramming of a real-time optical camera. The camera is linked to the process controller and triggers the ejection of trays containing faulty ampoules. Eight defect types are of interest, namely: missing ampoules; ampoules without a label; crushed ampoules; ampoules with a broken tip – present or missing; ampoules with a broken base; cracked ampoules; empty ampoules. The original inspection system performance was inadequate and only detected 2 of the 8 defect types reliably. The improved system which is described in this paper has adequately detected all aforementioned defect types. Experiments show that the overall detection rates have improved from 55% to 99.6% on average. Average camera detection accuracy has improved from 38% to 99.5%. In addition, the false positives, i.e. rejection rates, were reduced from 45% to 7%.
Walid Khraisat, Wisam Abu Jadayil, Yazan Al-Zain, Sa’ed Musmar, and Chaoqun Wu
Informa UK Limited
Abstract Since gas metal arc welding (GMAW) is a common procedure to join different sheets in the industry, the welding direction dependence on the rolling direction was investigated for a welded DP1000, a cold-rolled dual phase steel. Microstructural investigations and mechanical tests were conducted on two weldments; one being welded parallel to the rolling direction and the second transverse to the rolling direction and the results were compared. It was found that there is a higher degree of softening of the heat-affected zone in the sample welded parallel to the rolling direction. Although this softening did not significantly decrease the tensile strength or the hardness of this sample when compared to the one welded transverse to the rolling direction, the elongation was twice as high in the former sample. That is related to the slower heat dissipation in the sample welded parallel to the rolling direction as confirmed by its microstructural products.
Walid Khraisat, Wisam Abu Jadayil, Nathir Rawashdeh, and Henrik Borgström
Informa UK Limited
Abstract The contribution of the surface active element Phosphorus (P) in pore rounding in sintered steels is absent in popular sintering models. Instead, these mathematical models analyze the rate of mass transport, which, according to these models, is driven by chemical potential gradients set up by the differences in the curvature of the free surfaces of the compact of contacting particles. To elucidate the effect that P has on rounding of pores in sintering models, an attempt has been made to incorporate surface curvature in Gibbs’ surface thermodynamics. Using the image analysis method, a comparative study of pore morphology of sintered Iron-Carbon-Phosphorus (Fe-C-P) has been performed to study the effect P has on pore morphology. The application of the shape factor has been used to characterize the morphology of the pores. It was found that morphological enrichment and depletion of P are related to surface stresses as well as to the influence of vacancies.
W. Khraisat, N.A. Rawashdeh, and L. Nyborg
Elsevier BV
Wisam Abu Jadayil, Walid Khraisat, and Mwafak Shakoor
Informa UK Limited
Abstract In this paper a case study of a company was studied to determine the main factors affecting its production capacity, and study their influence to improve the production capacity to reach the optimum. Different aspects were investigated, including the speed of the running machines, the number of workers running each machine, the operating shifts, the machines utilization and the working environment. Data were collected for the current situation, then suggested solution were implemented for each aspect and effect on improving the production capacity was realized. It was found that all these factors have significant effect on improving the production capacity. Machines should be utilized effectively and run at the optimum speed, to improve the production and avoid extra maintenance cost. Moreover, as the working environment is improved, the productivity of workers is getting better, which will be reflected on the company overall production. Resource allocation and rescheduling the working shifts helped significantly in improving the productivity as well.
Mohammad Hayajneh, Mohammad D. AL-Tahat, Salman Alshobaki, and Walid Khraisat
Trans Tech Publications, Ltd.
This paper aims to examine the opportunities for possible improvement of the systems of pattern design and manufacturing, as well as the processes of casting design and technology in steel foundries. Solving these problems will improve the casting quality, and it will also standardize the work in one of the major bottlenecks in the production of steel casting. One big Jordanian foundry is selected as a case study. The foundry is referred to as GAZAL throughout this paper. A detailed flow process chart for the pattern making process with standardized times is developed, then possible improvements to the process are proposed. Several important milestones were developed and documented, among that; the development of a complexity classification and coding scheme of 6 levels to classify the products that GAZAL produced based on several criteria’s; the development of a mathematical model that relate the production time of the pattern with the complexity level. Finally conclusions are presented at the end of the paper.
W. Khraisat
SAGE Publications
Different alloys of the system Fe–C–Si were sintered to obtain a grey iron microstructure and then hardened by post-sintering heat treatment to obtain a martensitic structure. The main problem in the development of this approach is related to the occurrence of surface blistering in the as sintered material when sintering in N2 atmosphere. Surface blistering is explained by the increase in entrapped gas pressure in pores caused by graphite pore filling. A mechanism has been proposed to explain graphite pore filling. According to this mechanism, graphite pore filling is caused by the C activity difference between the gas entrapped in pores and the matrix, which is a consequence of Boudouard's reaction. This difference in C activity causes C to diffuse from the matrix to the pores, thus filling pores with graphite.
W. M. Abu-Jadayil and W. A. Khraisat
SAGE Publications
Fatigue life investigations have been made for hollow rollers in pure normal loading. Different hollowness percentages between 20 and 80% have been tested to find the optimum percentage hollowness that gives the longest fatigue life. Two main models were built for this purpose: model 1 with two identically sized rollers and model 2 with two non-identically sized rollers. In each model, two cases have been studied: when both rollers are hollow and when one roller is hollow while the other one is solid. The Ioannides–Harris (IH) theory was used to calculate the relative fatigue life of the hollow rollers with respect to solid rollers under the same loading. Investigations have been made for five different materials: CVD 52100, carburised steel, VIMVAR M50, M50NiL and induction hardened steel. The finite element package ABAQUS has been used to study the stress and deformations in the loaded rollers. In general, the optimum hollowness percentage with the longest fatigue life ranges between 60 and 70% based on the kind of the material, whether the rollers are of the same or different size and whether one or both rollers are hollow. Using the IH theory for fatigue life calculation resulted in having infinite fatigue life for those rollers made of induction hardened steel that relatively has high fatigue limit value. Rollers in the optimum range are flexible enough to get the best redistribution of stress in the contact zone. For models of a hollow cylindrical roller in contact with a solid roller, the optimum hollowness is around 70%. When both cylindrical rollers are hollow, the optimum hollowness decreases between 60 and 65%. At the optimum hollowness, small differences in the fatigue life have been found between models of one hollow roller and models of two hollow rollers, even though having both hollow rollers means less weight, thus saving more material and more stability for the system.
W. Khraisat, H. Borgström, L. Nyborg, and W. Abu al Jadayil
SAGE Publications
The grey iron microstructure Fe–2C–2Si powder based compact is tailored by different kinds of in situ and post sintering processing. This has been achieved by combining thermodynamic and kinetics modelling of microstructure development with sintering and controlled heat treatment experiments of tensile test specimens die compacted at 600 MPa. Applying optimised sintering conditions led to a grey iron like microstructure with 95% relative sintered density. Sinter hardening the compacts led to 500 MPa in yield strength and 600 MPa in ultimate tensile strength in combination with ductile fracture. Quenched and tempered condition showed the same strength values, but combined with brittle fracture due to martensitic structure. Pore rounding and partial pore filling by graphite were obtained by austenising isothermal hold during the cooling of the sintering cycle.
W. Khraisat, L. Nyborg, and P. Sotkovszki
SAGE Publications
Abstract Liquid phase sintering of M3/2 grade high speed steel (HSS) was carried out at 1270°C in high vacuum reaching near full density starting from loose packed powder. Focus is placed on the study of the effects of the addition of Si, Ni and V as elemental powder and cooling rates on the as sintered microstructure, the main objective being improving M6C characteristics and control of pearlite appearance. Slow cooling from the sintering temperature and Si addition in wt% resulted in a completely fine pearlitic matrix with less elongated and more uniformly distributed M6C precipitates. Adding V or Ni in wt-% quantities decreased the amount of pearlite owing to MC formation and delayed pearlite formation. The study involved the use of thermodynamic modelling and sintering cycle optimisation as well as the evaluation of sintered material by means of optical and scanning electron microscopy, X-ray diffraction and hardness testing.
P. Romano, O. Lyckfeldt, and W. Khraisat
SAGE Publications
Abstract The effects of water based shaping, by means of starch consolidation (SC), of an iron powder system regarding oxygen/carbon content and sintering performance were evaluated. Specifically, the influence of the drying conditions and the use of two different thickeners, xanthan gum and cellulose ether, were studied. The results showed that cellulose ether gave lower sintered density than xanthan gum, mainly because of less favourable rheological impact and air/gas entrapment at mould filling and consolidation. Due to less oxidation at drying and less removal of carbon at sintering, freeze dried specimens sintered to a higher density than room temperature air dried ones. The degree of oxidation and removal of carbon also influenced the as sintered microstructure. Ferrite grains surrounded by iron phosphide were found in both air dried and freeze dried specimens. However, the higher carbon content in freeze dried specimens also resulted in a significant amount of iron carbide grains (inclusions), which can be a potential strength limiting factor.
W. Khraisat and L. Nyborg
SAGE Publications
Abstract This paper provides data on the effect of carbon and phosphorus levels on the density of liquid phase sintered steel and the impact of subsequent carbon removal on the mechanical properties. After sintering die pressed samples composed of liquid forming additives and coarse water atomised powder at 1250°C or below, followed by postsintering decarburisation, densities of >95% relative density and non-brittle microstructures are achieved. Tensile testing shows the important effect of the microstructure on the mechanical properties. Ductility is improved by the post-sintering decarburisation, corresponding to elongation to fracture of 12% for certain compositions. Apparent diffusion coefficients for carbon were also estimated.
W. Khraisat and L. Nyborg
SAGE Publications
Abstract Powder mixtures composed of liquid forming master alloy powder and coarse iron powder were sintered to near full density by having a high amount (20 wt-%) of liquid phase during sintering. This was made possible by the use of the Fe-P-C system with or without Cu. Without post-sintering treatment, a brittle microstructure was obtained. By means of altered C and P control and decarburisation heat treatment of the as sintered material, the final non-brittle microstructure was achieved. Using the open porosity and liquid phase as a diffusion path, rapid decarburisation is created and the local combination of carbon and phosphorus in the microstructure is avoided. In this way, iron phosphide is not formed on grain and/or particle boundaries. Presence of pores is confirmed to be beneficial for grain growth control.