Fracture analysis of spot-welds with edge cracks using 2-D hybrid special finite element

This paper employed a systematic analysis using a 2-D hybrid special finite element containing an edge crack in order to describe the fracture behavior of spot-welds in automotive structures. The 2-D hybrid special finite element is derived form a mixed formulation with a complex potential function with the description of the singularity of a stress field. The hybrid special finite element containing an edge crack can give a better description of its singularity with only one hybrid element surrounding one crack. The advantage of this special element is that it can greatly simplify the numerical modeling of the spot welds. Some numerical examples demonstrate the validity and versatility of the present analysis method. The lap-shear, lap-tension and angle-clip specimens are analyzed and some useful fracture parameters such as the stress intensity factor and the initial direction of crack growth are obtained simultaneously.

Prediction of ductile fracture in the cold forging of steel

The thesis describes the development of a model of the cold forging process that accurately predicts the initiation of ductile fracture. The effect of the deformation history of the material during multiple forming operations is considered. Both two- and three-dimensional numerical models of the forging process were combined with a ductile fracture criterion to predict the material ductility and damage distribution in the workpiece.

Fracture analysis of spherical shells : application to cracking of macadamia nuts

The main consideration in recovering the macadamia kernal is to crack the spherical nutshell without damaging the kernal. Five mechanical cracking tools were tested, and the fracture mechanisms of nutshells, under various cracking loads, were studied. A classical theoretical approach and a numerical method were both used to investigate the influence of crack face closure on the stress intensity factor for a cracked spherical shell subjected to membrane forces and bending moments.

Fracture behaviour of a rapidly cured polyethersulfone toughened carbon fibre/epoxy composite

An out-of-autoclave rapid heating/low pressure technique has been used to cure polyethersulfone (PES) toughened HexPly 8552. Mode I and mode II tests were conducted to evaluate the fracture toughness of the composites and the effectiveness of cure was determined through thermal analysis. When compared to the autoclave process, the out-of-autoclave process resulted in a 52% reduction in processing time, without any sacrifice to the matrix intrinsic properties. Thermal analysis indicated an 8 °C improvement in glass transition temperature (T_g) as a result of an increased degree of cure. The out-of-autoclave process did lack in the ability to facilitate the removal of porosity which affected the fracture toughness results. The porosity is believed to have increased the mode I propagation fracture toughness. However its effect on mode II was quite deleterious, shown by scanning electron microscopy (SEM). This study managed to identify a number of key parameters associated with the out-of-autoclave process essential for further optimisation.

Fracture toughness of titanium foams for medical applications

The fracture behavior of titanium open foam is characterized and the R-curves of crack propagation from pre-cracks are measured. The crack growth has been optically observed, the measured initiation toughness, J_IC, has been analyzed and the effect of material morphology on the J_IC is discussed. The fracture toughness was found to be dependent on the expanding crack bridging zone at the back of the crack tip. The compact tension specimens also have some plastic collapse along the ligaments and it has shown that the titanium foam with a higher relative density is tougher. The non-uniform stressing within the plastic zone at the crack tip and the plastic collapse of cell topology behind the tip was found to be the primary cause of the R-curve behavior in low relative density titanium foams.

Fracture of DP590 steel : a multi-scale modeling approach

Advanced high strength steel sheets are one of the higher strength advance material developed by the steel industry for automotive bodies. One of the categories of this advanced high strength steel is Dual Phase (DP) steel. This steel consists of a two phase microstructure where soft and hard phase acts together to offer a high strength composite effect. The combination of high strength and ductility exhibited by these sheets allows the design and manufacture of complex parts. However, during forming certain grades of DP steel sudden cracking can occur without any intimation of necking. This abnormal forming behavior is difficult to accurately predict because most classical modelling approaches are not designed for such micro-structurally heterogeneous materials. These modelling approaches are generally based on an average representation of the material behaviour in a continuum mechanics formulation. This works for materials that are homogenous, or at least could be assumed to be homogenous at scales lower than the naked eye can see. However, for a material like advanced high strength steel, the microstructure plays a significant role in dictating the mechanical behavior at the macro-scale. This paper studies the forming and fracture behavior through multi-scale modeling of DPO590 steel. It is found that the sufficient accuracy can be achieved from multi-scale modeling when comparing with experiments.

Bone mineral density and incidence of hip fracture in Swedish urban and rural women 1987–2002

Background and purpose Although the incidence of hip fracture during the past 50 years has increased, a break in this trend has been reported in the last decade. Whether this change is attributable to changes in bone mineral density (BMD) or whether it varies between urban and rural regions is unknown.

Methods We evaluated changes in annual hip fracture incidence in women aged ≥ 50 years in one urban population (n = 51,757) and one rural population (n = 26,446) from 1987 to 2002. We also examined secular differences in BMD (mg/cm2), evaluated by single-photon absorptiometry at the distal radius, prevalence of osteoporosis, and several other risk factors for hip fracture in one population-based sample of urban women and one sample of rural women aged 50–80 years at two time points: 1988/89 (n = 257 and n = 180, respectively) and 1998/99 (n = 171 and n = 118, respectively).

Results No statistically significant changes were evident in annual age-adjusted hip fracture incidence per 104 when analyzing all women (–0.01 per year (95% CI: –0.37, 0.35)), rural women (–0.38 per year (-1.05, 0.28)), or urban women (0.19 per year (–0.28, 0.67)). BMD (expressed as T-score) was similar in 1988/99 and 1998/99 when analyzing all women (–0.09 (–0.26, 0.09)), urban women (–0.04 (–0.27, 0.19)), or rural women (–0.15 (–0.42, 0.13)) women.

Interpretation Since no changes in age-adjusted hip fracture incidence and no differences in BMD were found during the study period, changes evident in the other risk factors for hip fracture that we investigated (such as gait velocity and balance) are either of minor importance or are counteracted by changes in other risk factors.

Association between hyperglycaemia and fracture risk in non-diabetic middle-aged and older Australians : a national, population-based prospective study (AusDiab)

Summary : The association between pre-diabetes and fracture risk remains unclear. In this large cohort of middle-aged and older Australian men and women without diabetes, elevated 2-h plasma glucose and pre-diabetes were associated with a reduced 5-year risk of low trauma and all fractures in women, independently of BMI, fasting insulin and other lifestyle factors.

Introduction : We aimed to (1) examine associations between fasting and 2-h plasma glucose (FPG and 2-h PG), fasting insulin and risk of low trauma and all fractures in non-diabetic adults and (2) compare fracture risk between adults with pre-diabetes (impaired glucose tolerance or impaired fasting glucose) and those with normal glucose tolerance (NGT).

Methods : Six thousand two hundred fifty-five non-diabetic men and women aged ≥40 years with NGT (n = 4,855) and pre-diabetes (n = 1,400) were followed for 5 years in the AusDiab Study. Fractures were self-reported.

Results : Five hundred thirty-nine participants suffered at least one fracture (368 women, 171 men), of which the majority (318) occurred after a low-energy trauma (258 women, 60 men). In women, a 2-h PG ≥7.2 mmol/L (highest quartile) was associated with a decreased risk of low trauma and all fractures independent of age and BMI [OR (95% CI) for low trauma fractures, 0.59 (0.40–0.88)], but also fasting insulin, smoking, physical activity, history of fracture, dietary calcium and alcohol intake or menopausal status. There was no effect of 2-h PG on fracture risk in men [OR (95% CI), 1.39 (0.60–3.26)] or any relationship between fracture risk and quartiles of FPG or insulin in either sex. Compared to women with NGT, those with pre-diabetes had a reduced risk of fracture [OR (95% CI) for all fractures, 0.70 (0.52–0.95); for low trauma fractures, 0.75 (0.53–1.05)].

Conclusion : Elevated 2-h PG levels and pre-diabetes were inversely associated with low trauma and/or all fractures in non-diabetic women, independent of BMI and fasting insulin levels.