A client (Advanced Hydraulics, Inc.) has inquired about forensicengineering. Given your recent design experience with this client'sproducts, I thought you might be able to address some of theconcerns raised here. After roughly ten years of service,three identical hydraulic presses manufactured by AdvancedHydraulics have failed in similar fashions. In one instance, afailed cylinder was welded and returned to service without athorough investigation. Examining the failures of the second andthird cylinders, however, revealed similar types offailure. As illustrated in Figure 1, each fractured cylinderwas sealed with a flat head. Fig. 2 depicts the relevant dimensionsand locations of the fracture-causing cracks. Figure 3 depicts theappearance of the head's inner surface and the fracture.
The following are the characteristics and operation of thecylinder: The cylinder was composed of steel and had a Brinellhardness of 163. (equivalent to a tensile strength of 79,920 psi).The material's yield strength is assumed to be 44,800 psi. Themicrostructural analysis revealed a carbon content between 0.3 and0.4 percent and did not reveal the presence of significantinclusions or segregates that could have contributed to thefailure. Initial operating conditions included pressure of 750 psi,which eventually rose to 4,480 psi.
Consider both the longitudinal stress imposed by the pressurevessel stresses and the bending stress imposed by the closed, flatend in your analysis. Consider the stress concentration at thesharp corner. Consider whether a fracture mechanics approach to thebrittle fracture from the fatigue crack is reasonable for thismaterial (you will need to determine or estimate the material'sfracture toughness).
Based on your knowledge of fatigue and fracture as well as theproper design for fatigue, Do the following parts A and B
a) recommend corrective action to prevent fracture in otherhydraulic cylinders of the same design and material, and
b) redesign the cylinder end area to eliminate failures of thistype.
A Client Advanced Hydraulics Inc Has Inquired About Forensic Engineering Given Your Recent Design Experience With T 1 (989.33 KiB) Viewed 33 times
Figure 1 View of failed cylinder Figure 2 Dimensions of cylinder/location of crack Figure 3 Appearance of internal face of cylinder end showing duplex nature of fracture
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